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IN THIS VOLUME


ASME Conference Presenter Attendance Policy and Archival Proceedings

2013;():V009T00A001. doi:10.1115/IMECE2013-NS9.
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This online compilation of papers from the ASME 2013 International Mechanical Engineering Congress and Exposition (IMECE2013) represents the archival version of the Conference Proceedings. According to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures and Fluids: Composite Materials for Renewable Energy Systems

2013;():V009T10A001. doi:10.1115/IMECE2013-63035.

Matrix damage, involving transverse and shear cracks, is a common failure mode for composite structures, yet little is known concerning their interaction. A modified Iosipescu coupon is proposed to study the evolution of the shear and transverse damage and their mutual effects. The layup and coupon geometry were selected in a way that controls the severity of the damage and allows the measurement of shear and transverse stiffness degradation directly. The results were compared to material degradation models where damage was dominated by matrix failure. While positive agreement was generally observed in the transverse direction, no model was able to predict the observed shear damage. A new elasticity solution was, therefore, proposed for the shear stress-strain field of a transversely cracked laminate. The approach used a classical shear lag theory with friction applied to the crack surfaces. Using the constitutive relations, the shear modulus reduction was found as a function of crack density, and showed good agreement with experimental measures.

Commentary by Dr. Valentin Fuster
2013;():V009T10A002. doi:10.1115/IMECE2013-65549.

The regulations for environmental issues on the use of fossil energy and the upsurge of the power demand due to the improving standard of living worldwide increasingly require the development of renewable energy sources. In particular, developing countries suffer from severe lack of energy because they do not have technical ability for large-capacity generation facilities, such as thermal or nuclear power generation plants, and financial capacity to procure the resources. Therefore, most countries are trying to develop the renewable energy sources, especially the solar generation facilities. In the solar power generation system, the structural stability of the support unit that supports the large-area solar panel is essential to ensure the high generation efficiency and the long life of the system. According to the international standards and industry practice, the solar power system must be stable against the 120 km/h wind and its life must be 20 years or longer. The solar panel for the solar generation system are made by combining ten to several tens of solar modules depending on the scale of the system. This generates a load of at least 250 kg, and if the aerodynamic force due to the strong wind is additionally applied, the severe ground settlement of the support unit on the weak ground may damage the system. In this study, the structure of the solar power system, which can operate stably in the areas with weak ground, such as Laos and Vietnam, is proposed. Diverse load distributions and structure deformations were calculated via numerical analysis, and the typical ground characteristics of the subject areas were considered to determine the structure that minimizes the settlement.

Commentary by Dr. Valentin Fuster
2013;():V009T10A003. doi:10.1115/IMECE2013-65638.

A model is proposed which relates externally applied tensile stresses to changes in absorption capacity as well as diffusion rate. The model postulates that changes seen in the diffusion process are the result of stress-dependent changes in the free volume of the epoxy resin. The free volume changes of the resin are calculated through laminate plate theory, which itself becomes a function of fiber angle as well as a host of elastic properties of the constituents. Consequently, according to the proposed model, changes in diffusion parameters are dependent upon the magnitude of applied stress, the loading angle, as well as elastic properties of the constituents.

Additionally, a finite element model is presented. The proposed finite element model establishes an analogy between thermal and mass diffusion for use in solving the moisture diffusion problems, both in free and stressed states. Input parameters for the FE model are found through use of the previously established mathematical diffusion model.

In order to experimentally verify the proposed models, a series of epoxy glass laminate samples were manufactured at varying fiber angles and immersed in a moist environment while subjected to varying levels of tensile loading. Weight gain measurements were recorded throughout the diffusion process until full saturation was achieved. The experimental values exhibited excellent agreement with both the suggested theoretical model and the finite element model.

Commentary by Dr. Valentin Fuster
2013;():V009T10A004. doi:10.1115/IMECE2013-65647.

The current work is focused on numeric investigation of aerodynamic load developed on a wind turbine blade and its effects on aeroelastic characteristics of a wind turbine blade. In order to do that proper turbulent model along with appropriate assumptions need to be determined. Geometry is modeled with actual blade data for both twist and tapper. Blade tip is not considered during the modeling. Validation is done by NREL phase VI wind turbine blade data as well as other published data. Finally the aerodynamic load obtained from the CFD simulation is transferred to perform the structural analysis. It has been found that the load distribution along the blade span is not linear. It varies with the span length and it also varies along the chord of the blade airfoil. Due to this varying load the stresses developed in the blade is dissimilar which dictates the skin thickness of the blade and the shape of the spur inside the blade. It has also been observed that the aerodynamic characteristics such as lift coefficient (CL) and pressure coefficient (CP) changes with the deflection of the blade which affects the power output of the wind turbine.

Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures and Fluids: Durability and Life Prediction of Advanced Composite Materials

2013;():V009T10A005. doi:10.1115/IMECE2013-63415.

With an industrial increasing interest in sustainable, eco-efficient and green material’s application, natural fiber in polymer composite is guided to develop rapidly, especially kenaf nonwovens in making automotive interior trim parts with its comparative excellent strength and renewability. The objectives of this research are to investigate the environmental degradation behavior on the physical and mechanical properties of kenaf/unsaturated polyester nonwoven composites (KUNC) with special reference to the influence of different geographic natural climate ageing conditions. KUNC was prepared with needle-punched kenaf’s impregnation into unsaturated polyester resin assisted with vacuum oven following by hand lay-up molding. Natural environmental degradation was performed on KUNC by exposing the specimens to Kyoto(Japan), Shanghai(China) and Harbin(China) for a period of 3 months. Weight change and mechanical properties of degraded KUNCs in former three geographic positions in terms of tensile, flexural, impact and fracture toughness were measured instrumentally for ageing effect discussion and comparison. As expected, the aged specimens in those different positions all showed the dropped mechanical properties with weight increasing in varying degrees. Furthermore, the result of degradation level comparison among different positions revealed the positive correlation between increased weight percentages and dropped mechanical properties. In other words, dropped mechanical properties of the degraded composites with increasing weight were attributed to the effect of water, which deteriorates the interfacial properties of composites.

Commentary by Dr. Valentin Fuster
2013;():V009T10A006. doi:10.1115/IMECE2013-63727.

Water percolation into coating-metal interface is usually the main cause for the deterioration of corrosion protective property of organic coatings, which leads to coating delamination and under film corrosion. Recently, flowing fluid has received attention due to its capability to accelerate the degradation of materials. A plethora of works have focused on the corrosion of metallic materials accelerated by the flow of working fluids, while few studies have investigated the flow accelerated degrading behavior of organic coatings. For organic coatings, flowing fluid above the coating surface affects corrosion by enhancing the water percolation and by abrading the surface due to wall shear stress. Hence, it is of great importance to understand the influence of flowing fluids on the degradation of corrosion protective organic coatings.

In this study, a commercially available epoxy based clear coating and pigmented marine coating were exposed to the laminar flow as well as stationary immersion. The laminar flow was pressure driven and confined in a newly designed flow channel. A 3.5 wt% sodium chloride solution was employed as the working fluid with a variety of flow rates. The corrosion protective properties of organic coatings were monitored inline by Electrochemical Impedance Spectroscopy (EIS) measurement. Equivalent circuit models were employed to interpret the EIS spectra. The time evolution of coating resistance and capacitance obtained from the model was studied to demonstrate the coating degradation. Thickness, gloss, and other topography characterizations were conducted to facilitate the assessment of the corrosion. The immersing solutions were measured by pH and conductivity meters as well as Fourier Transform Infrared Spectrometer (FTIR) to trace coating degradation products as they leached out from the coating. Initial attempts to acquire acceleration factors and predict service lifetime of organic coatings were also conducted.

Commentary by Dr. Valentin Fuster
2013;():V009T10A007. doi:10.1115/IMECE2013-64436.

A thermodynamic framework for chemically reacting systems is put to use in kinetic modeling of any chemical system with N species undergoing M reactions. A new approach of deriving kinetic models from a Gibbs potential, of multivariate polynomial function, is demonstrated with an example of single reaction system involving three species. Also, the usual first order kinetics is deduced as a special case in the example. The distinct advantages of the new approach lies in obtaining the evolution of concentrations of species, their individual chemical potentials and the specific Gibbs potential and is demonstrated for a single reaction system as an example. Oxidation in polymer composites is studied with a coupled reaction-diffusion model obtained using first order kinetics and is solved for a boundary value problem that predicts the concentration of species over space and time. Concentration of oxidized products is correlated with modulus of aged sample and degradation effects is calculated in case of simple torsion.

Commentary by Dr. Valentin Fuster
2013;():V009T10A008. doi:10.1115/IMECE2013-64475.

As well known, natural fibers absorb water easily that will affect the mechanical property considerably and there exists a problem of incompatibility which leads the weak interfacial adhesion between the fiber and the resin matrix because of the hygroscopic nature of natural fibers. Therefore, conducting hot water immersion and tensile test is necessary to study the mechanical property and degradation. In this study, glass fiber/wood powder/pp. hybrid composites were prepared by injection molding process at a fixed reinforcement to matrix ratio of 51:49. 3 kinds of hybrid specimens with glass fiber/wood powder ratios of 51:0, 21:30, and 0:51 were fabricated. The hydrothermal aging performance was investigated during the 80°C hot water immersion experiment with a series of immersion time and the effect of hot water immersion on the mechanical properties of composites have been evaluated based on the tensile test.

Results showed that both the strength and modulus of hybrid composite decrease obviously as the immersion time increase, which can be considered that the hydroscopic property of natural fiber would decrease the durability of composite in humidity environment. And the skin-core structure comes from injection molded process contributes to the better hydrothermal aging property of Glass/PP composite.

Commentary by Dr. Valentin Fuster
2013;():V009T10A009. doi:10.1115/IMECE2013-65671.

The effect of nanoclay on the degradation of low velocity impact responses of carbon fiber reinforced polymer (CFRP) composites manufactured by the vacuum assisted resin transfer molding (VARTM) process is experimentally investigated with and without exposure to seawater for marine applications. Nanoclay was dispersed into the matrix by using magnetic stirring. Samples (100 mm by 100 mm) exposed to seawater for 0, 6, and 12 months in laboratory conditions were impacted at 20, 30, and 40 J energy levels using a Dynatup8210. The damage sustained by the samples was evaluated by a thermographic imaging technique. Comparisons between conventional and nanophased CFRP composites both in conditioned and unconditioned cases were made in terms of peak force, absorbed energy, deflection, delamination area, and specific delamination energy. Water absorption was observed to be reduced due to nanoclay infusion. After 12 months of exposure to seawater 2% nanophased samples absorbed 0.39% moisture whereas control samples absorbed 0.67% moisture. Impact strength, toughness, and energy absorption decreased with increasing conditioning time by weakening the bond between the fiber and matrix and softening the matrix materials. However, reduction in properties is significantly extenuated by the incorporation of nanoclay in the matrix. Specific delamination energy (SDE) is observed to be higher in the nanophased CFRP compared to that of the conventional one at different aging periods indicating an enhanced toughness in the nanophased composites. The larger and stronger interfacial area produced by the nanoclay inclusion has been found to facilitate more energy absorption in the nanophased sample compared to the conventional one. Furthermore, nanoclay reduced the development of delamination by arresting the crack propagation path or by toughening the matrix. It is concluded that the excellent barrier capacity, higher surface area, and high aspect ratio of nanoclay are responsible for the superior performance of CFRP composites, which in turn, enhances the durability of composites.

Commentary by Dr. Valentin Fuster
2013;():V009T10A010. doi:10.1115/IMECE2013-66771.

In this study, we report the self-healing of e-glass/epoxy composites achieved through embedding self-healing agents (SHA) filled hollow glass fibers (HGFs). At first, catalytic technique was used to fill bonded HGFs with SHA. The HGFs were then laid on e-glass fibers and the laminates were fabricated using vacuum assisted resin molding (VARIM) technique. Low-velocity impact tests at two different energy levels were conducted multiple times in the closest proximity to determine the healing efficiency. Optical microscopic study was done to see the changes in the SHA filled HGFs samples before and after impact. Results showed significant recovery of impact properties with 4.47% lost in peak load after second impact in SHA samples whereas it was 27.7% in control samples. The loss in energy to peak load was 20.44% in SHA filled samples, whereas 41% in control samples. Optical microscopy images showed filling of cracks produced after impact with SHA reflecting the significant recovery of impact properties.

Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures and Fluids: Failure Mechanics of Advanced Materials and Structures

2013;():V009T10A011. doi:10.1115/IMECE2013-66566.

Modeling and characterization of complex composite structures is challenging due to uncertainties inherent in these materials. Uncertainty is present at each length scale in composites and must be quantified in order to accurately model the mechanical response and damage progression of this material. The ability to pass information between length scales permits multiscale models to transport uncertainties from one scale to the next. Limitations in the physics and errors in numerical methods pose additional challenges for composite models. By replacing deterministic inputs with random inputs, stochastic methods can be implemented within these multiscale models making them more robust.

This work focuses on understanding the sensitivity of multiscale models and damage progression variations to stochastic input parameters as well as quantifying these uncertainties within a modeling framework. A multiscale, sectional model is used due to its efficiency and capacity to incorporate stochastic methods with little difficulty. The sectional micromechanics in this model are similar to that of the Generalized Method of Cells with the difference being the discretization techniques of the unit cell and the continuity conditions. A Latin Hypercube sampling technique is used due to its reported computational savings over other methods such as a fully random Monte Carlo simulation. Specifically in the sectional model, the Latin Hypercube sampling method provides an approximate 35 % reduction in computations compared to the fully random Monte Carlo method. The Latin Hypercube sampling is a stratified technique which discretizes the distribution function and randomizes the input parameters within those discretized fields. Within this multiscale modeling framework, a progressive failure theory is implemented using these stochastic methods and a modified Hashin failure theory. With a combined stochastic method and progressive failure theory, this multiscale model is capable of modeling the uncertainty and material property variations for composite materials.

Commentary by Dr. Valentin Fuster
2013;():V009T10A012. doi:10.1115/IMECE2013-66836.

The future development of body armor is to develop a lightweight, and wearable garment system without a loss of ballistic impact resistance. High performance fabrics, such as Kevlar, have been utilized for body armor due to their high energy absorption and lightweight characteristics. However, additional reinforcement is necessary for Kevlar fabric to meet the protection requirements for body armor against typical ballistic threats. Thick layers of fabric or embedded ceramic plates have been used to meet these requirements at the expense of increased weight of the armor and reduced mobility of the user. Thus, much research has been conducted on this topic to increase the ballistic impact resistance of Kevlar fabrics, mainly focused on the understanding and modeling of ballistic impact behavior. Due to the significant effect of damage mechanisms on ballistic impact response, these mechanisms should vastly be studied to better understand the ballistic impact response of Kevlar. When a projectile impacts a woven fabric, the imparted energy is dissipated through several damage mechanisms including tow pullout, local tow failure at the point of impact, and remote tow failure. Among those mechanisms, tow pullout is especially critical in the case of a penetrator with a blunt face impacting a fabric with non-penetrating velocities and is strongly influenced by friction between tows. In this work, we employed a novel method to increase the friction between Kevlar tows by synthesizing zinc oxide nanowires onto the fabric surface. As a result, vertically-aligned zinc oxide nanowires were grown on the fabric surface and tailored to achieve an optimum ballistic performance response reaching an enhancement of up to 390% in tow pullout peak load compared to untreated fabrics. Additionally, the effect of various surface functionalization processes and nanowire morphology is investigated so that an optimum process is developed for an efficient ballistic performance response.

Topics: Textiles , Nanowires
Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures and Fluids: Fatigue and Fracture of Engineering Materials and Structures

2013;():V009T10A013. doi:10.1115/IMECE2013-63163.

Parts and structures are often welded together in different ways, as it is cost and weight effective in comparison to conventional bolted and riveted joints. Steel followed by aluminum alloys, are the most frequently welded metal. Welding results in inhomogeneous and different materials near the joint which may lead to defects. These defects may be the cause of initiation and development of cracks as a result of cyclic loading. In the present work fatigue crack growth rate of a mild steel plate welded by friction stir welding (FSW) has been studied under constant amplitude load with different values of R-ratio. Hardness in the base metal was found to be low in comparison to thermo-mechanically affected and weld nugget zone. Grain size of weld zone was much smaller to base metal and it was the same to heat affected zone and base metal. A C-T specimen with notch at welded and non welded region was tested to get the behavior of Fatigue Crack Growth (FCG) at different zones. It has been found that the fatigue crack growth rate in welded material is lower as compared to base material.

Commentary by Dr. Valentin Fuster
2013;():V009T10A014. doi:10.1115/IMECE2013-63779.

Pt-20%Ir coils were used in medical devices as conductors for the leads that transfer the electrical signal from an implanted stimulator to the area of the body (e.g., brain or nerves) to be stimulated. In this study, the fatigue behavior and failure mechanism of Pt-20%Ir coils was studied with axial fatigue testing. The stress and strain on the coils was analyzed with the non-linear FEA (finite element analysis) software ABAQUS. A strain vs. fatigue curve was obtained. A SEM (scanning electron microscope) was used to analyze the fatigue fracture surface of the samples.

Commentary by Dr. Valentin Fuster
2013;():V009T10A015. doi:10.1115/IMECE2013-63961.

An analysis was performed to predict the failure load of unidirectional and woven pinned loaded composite joints using the characteristic curve model. The characteristic dimensions used to determine the characteristic curve were evaluated from stress functions without experimental tests. A parametric study was carried out for different coefficient of friction ranging between 0 and 0.15 to evaluate the effect of friction on joints failure using Tsai-Wu failure criterion along the characteristic curve. A comparison of analytical results with the available experimental data showed that the friction coefficient of 0.05 generally gave the best prediction for the joint configurations evaluated.

Commentary by Dr. Valentin Fuster
2013;():V009T10A016. doi:10.1115/IMECE2013-64314.

In order to make clear the mechanism of the directional coarsening (rafting) of γ′ phases in Ni-base superalloys under uni-axial tensile strain, molecular dynamics (MD) analysis was applied to investigate effects of alloying elements on diffusion characteristics around the interface between the γ phase and the γ′ phase. In this study, a simple interface structure model corresponding to the γ/γ′ interface, which consisted of Ni as γ and Ni3Al as γ′ structure, was used to analyze the diffusion properties of Ni and Al atoms under tensile strain. The strain-induced anisotropic diffusion of Al atoms perpendicular to the interface between the Ni(001) layer and the Ni3Al(001) layer was observed in the MD simulation, suggesting that the strain-induced anisotropic diffusion of Al atoms in γ′ phase is one of the dominant factors of the kinetics of the rafting during creep damage. The effect of alloying elements in the Ni-base superalloy on the strain-induced anisotropic diffusion of Al atoms was also analyzed. Both the atomic radius and the binding energy with Al and Ni of the alloying element are the dominant factors that change the strain-induced diffusion of Al atoms in the Ni-base super-alloy.

Commentary by Dr. Valentin Fuster
2013;():V009T10A017. doi:10.1115/IMECE2013-65388.

Bi-material interfaces are prevalent in a broad range of natural and man-made components and systems. Failures often occur on the interface at a free edge, especially when the corresponding linear elastic solution exhibits a singularity in stress, which depends upon the material properties and the included angles of the two material bodies. In this paper, we combine finite element analysis and a compact self-organizing cellular automata-based genetic algorithm for topology optimization of the bi-material system. The objective is to eliminate stress singularities and furthermore to reduce peak interface stresses. The developed algorithm is applied to a simple bi-material plate in an attempt to maximize strength through geometric design.

Commentary by Dr. Valentin Fuster
2013;():V009T10A018. doi:10.1115/IMECE2013-65583.

Fretting is an important problem for the operators of turbine engines, and it occurs when the blade and disk are pressed together in contact and experience a small oscillating relative displacement due to variations in engine speed and vibratory loading. It is a significant driver of fatigue damage and failure risk of disks. The present effort focuses on the damage initiation and propagation due to fretting fatigue. It introduces a micro-thermo-mechanical damage model that is capable of capturing the micro-scale nature of the fretting small oscillatory relative displacement. The micro-scale capability of the damage model is required to capture the effect of very high local stress near the edge of contact, which results in wear, nucleation of cracks, and their growth. It also provides a high fidelity approach to capture the significant reduction in the life of the material at the blade to disk attachment. To further understand the role of damage in the fretting initiated fracture, a specially developed novel fretting crack initiation model is incorporated in the analysis. Such combination makes it possible to simulate the realistic mechanism associated with fretting. The models are incorporated in a fretting fatigue simulation of an actual blade and disk attachment configuration. The results are validated with data obtained from an actual blade and disk attachment test using a representative loading mission. The results show consistency and accuracy with experimental data.

Topics: Gas turbines , Disks , Blades
Commentary by Dr. Valentin Fuster
2013;():V009T10A019. doi:10.1115/IMECE2013-66076.

This work provides a numerical and experimental investigation of fatigue crack growth behavior in steel weldments including crack closure effects and their coupled interaction with weld strength mismatch. A central objective of this study is to extend previously developed frameworks for evaluation of crack closure effects on fatigue crack growth rates (FCGR) to steel weldments while, at the same time, gaining additional understanding of commonly adopted criteria for crack closure loads. Very detailed non-linear finite element analyses using 3-D models of compact tension C(T) fracture specimens with square groove, weld centerline cracked welds provide the evolution of crack growth with cyclic stress intensity factor which is required for the estimation of the closure loads. Fatigue crack growth tests conducted on plane-sided, shallow-cracked C(T) specimens provide the necessary data against which crack closure effects on fatigue crack growth behavior can be assessed. Overall, the present investigation provides additional support for estimation procedures of plasticity-induced crack closure loads in fatigue analyses of structural steels and their weldments.

Commentary by Dr. Valentin Fuster
2013;():V009T10A020. doi:10.1115/IMECE2013-66202.

Fatigue is the most critical failure mode of many mechanical component. Therefore, fatigue life assessment under fluctuating loads during component development is essential. The most important requirement for any fatigue life assessment is knowledge of the relationships between stresses, strains, and fatigue life for the material under consideration. These relationships, for any given material, are mostly unique and dependent on its fatigue behavior.

Since the work of Wöhler in the 1850’s, the uniaxial stress versus cycles to fatigue failure, which is known as the S-N curve, is typically utilized for high-cycle fatigue. In general, high cycle fatigue implies linear elastic behavior and causes failure after more than 104 or 105 cycles. However. the transition from low cycle fatigue to high cycle fatigue, which is unique for each material based on its properties, has not been well examined. In this paper, this transition is studied and a material dependent number of cycles for the transition is derived based on the material properties. Some implications of this derivation, on assessing and approximating the crack initiation fatigue life, are also discussed.

Topics: Fatigue , Cycles
Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures and Fluids: General

2013;():V009T10A021. doi:10.1115/IMECE2013-63183.

In this paper, Carrera’s Unified Formulation (CUF) is extended to perform free-vibrational analyses of rotating structures. CUF is a hierarchical formulation which offers a procedure to obtain refined structural theories that account for variable kinematic description. These theories are obtained by expanding the unknown displacement variables over the beam section axes by adopting Taylor’s polynomials of N-order, in which N is a free parameter. The linear case (N = 1) permits us to obtain classical beam theories while higher order expansions could lead to three-dimensional description of dynamic response of both rotors and centrifugally stiffened beams. The Finite Element method is used to derive the weak form of the three-dimensional differential equations of motion in term of fundamental nuclei, whose forms do not depend on the approximation used (N). The present formulations include gyroscopic effects and stiffening due to centrifugal stresses. In order to verify the accuracy of the new theories, several analyses are carried out and the results are compared with solutions presented in the literature in graphical and numerical form. The advantages of the variable kinematic models are evident especially when shafts with deformable discs and thin-walled rotating beams made up with composite materials are studied.

Commentary by Dr. Valentin Fuster
2013;():V009T10A022. doi:10.1115/IMECE2013-64787.

The paper deals with torsional stiffness and natural frequency of composite corrugated bellows type of expansion joint. In this paper simplified formulae are developed considering thin walled pipe model. Integration method is used to determine the natural frequency of bellows. The EJMA {1} method of calculating the torsional frequency is modified using two different equivalent radii. The results obtained by the modified method are compared with the finite element method and found to be in good agreement.

Commentary by Dr. Valentin Fuster
2013;():V009T10A023. doi:10.1115/IMECE2013-65119.

The AC electrothermal effect can improve the pumping rate by multiple folds compared to other eletrokinetic techniques in micro/nano scale. In this research, the AC electrothermal micropump velocity will be optimized by surface modification using a biocompatible hydrophobic nanocomposite monolayer. This coating will modify the micropump surface to a hydrophobic surface and reduce the friction losses at the liquid-solid interface, and eventually increase the micropumping velocity. The advent of microfabrication and integrated miniature pumps has applications on biomedical devices such as implantable glucose sensors. These micropumps require the transport of small amounts of fluids (μL range). When utilized in biomedical applications, micropumps can be used to administer small amounts of medication (e.g. insulin) at regular time intervals. These micropumps can also be integrated with the lab-on-a-chip devices and can provide inexpensive disposable devices. To demonstrate the fluid manipulation in high conductive bio-fluids, we have developed an optimized AC electrothermal micropump using symmetrical electrode arrays.

Commentary by Dr. Valentin Fuster
2013;():V009T10A024. doi:10.1115/IMECE2013-65202.

Electromagnetic (EM) waves, such as electronic noise and radio frequency interference can be regarded as an invisible electronic pollution which justifies a very active quest for effective electromagnetic interference (EMI) shielding materials. Highly conductive materials of adequate thickness are the primary solutions to shield against EMI. Equipment cases and basic structure of space aircraft and launch vehicles have traditionally been made of aluminum, steel and other electrically conductive metals. However, in recent years composite materials have been used for electronic equipment manufacturing because of their lightweight, high strength, and ease of fabrication. Despite these benefits, composite materials are not as electrically conductive as traditional metals, especially in terms of electrical grounding purposes and shielding. Therefore, extra effort must be taken to resolve these shortcomings. The present work demonstrates a study on developing hybrid composites based on fiberglass with surface grown carbon nanotubes (CNTs) for EMI applications. The choice of fiberglass is primarily because it naturally possesses poor electrical conductivity, hence growing CNTs over glass fiber surface can significantly improve the conductivity. The fabrics were sputter-coated with a thin layer of SiO2 thermal barrier prior to growing of CNTs. The CNTs were grown on the surface of woven fiberglass fabrics utilizing a relatively low temperature technique. Raw fiberglass fabric, SiO2 coated fabric, and SiO2 coated fabric which was subjected to the identical heat treatment as the samples with CNTs were also prepared. Two-layers composite specimens based on different surface treated fiberglass fabrics were fabricated and their EMI shielding effectiveness (SE) was measured. The EMI SE of the hybrid CNT-fiberglass composites was shown to be 5–10 times of the reference samples. However, the tensile mechanical properties of the composites based on the different above mentioned fibers revealed significant degradation due to the elevated CNT growth temperature and the addition of coating layer and CNTs. To further probe the structure of the hybrid composites and the inter-connectivity of the CNTs from one interface to another, sets of 20-layers composites based on different surface treated fabrics were also fabricated and characterized.

Commentary by Dr. Valentin Fuster
2013;():V009T10A025. doi:10.1115/IMECE2013-65396.

In this study the elastoplastic behavior of cantilever beams under a combined compressive axial load and an imposed lateral bending deflection are analyzed. Eventhough the particular condition of elastoplastic buckling has been studied before, the developed theories are limited to the prediction of the initial failure of the beam. In the current study the elastoplastic behavior of cantilever beams under compressive load at levels below the critical buckling load are studied in order to determine the remaining load bearing capacity of the beam under combined bending and axial loads, including the behavior at progressive levels of plastic deformation.

The elastoplastic bending process is analyzed using the finite element method. In particular, the analysis is focused on the evaluation of the limiting bending force necessary to increase or reduce the curvature of the beam in the plastic zone. The bending force depends on the compressive axial load, the geometrical dimensions of the beam, material coefficients, such as Young’s modulus and yield stress, and the hardening model. The large number of variables involved, is reduced by introducing two dimensionless load parameters.

The results of the analysis are presented and discussed for a wide range of dimensionless loads. Also the influence of work hardening on the obtained bending force is analyzed, comparing between an ideal plastic behavior and a bilinear plasticity model with a linear hardening behavior.

Commentary by Dr. Valentin Fuster
2013;():V009T10A026. doi:10.1115/IMECE2013-65599.

Nanocomposites; including nano-materials such as nano-particles, nanoclays, nanofibers, nanotubes, and nanosheets; are of significant importance in the rapidly developing field of nanotechnology. Due to the nanometer size of these inclusions, their physicochemical characteristics differ significantly from those of micron size and bulk materials. The field of nanocomposites involves the study of multiphase materials where at least one of the constituent phases has one dimension less than 100 nm. This is the range where the phenomena associated with the atomic and molecular interaction strongly influence the macroscopic properties of materials. Since the building blocks of nanocomposites are at nanoscale, they have an enormous surface area with numerous interfaces between the two intermix phases. The special properties of the nanocomposite arise from the interaction of its phases at the interface and/or interphase regions. By contrast, in a conventional composite based on micrometer sized filler such as carbon fibers, the interfaces between the filler and matrix constitutes have a much smaller surface-to-volume fraction of the bulk materials, and hence influence the properties of the host structure to a much smaller extent. The optimum amount of nanomaterials in the nanocomposites depends on the filler size, shape, homogeneity of particles distribution, and the interfacial bonding properties between the fillers and matrix. The promise of nanocomposites lies in their multifunctionality, i.e., the possibility of realizing unique combination of properties unachievable with traditional materials. The challenges in reaching this promise are tremendous. They include control over the distribution in size and dispersion of the nanosize constituents, and tailoring and understanding the role of interfaces between structurally or chemically dissimilar phases on bulk properties. While the properties of the matrix can be improved by the inclusions of nanomaterials, the properties of the fibers can also be improved by the growth of nanotubes on the fibers. The combination of the two will produce super-performing materials, not currently available. Since the improvement of fiber starts with carbon nanotube grown on micron-size fibers (and matrix with a nanomaterial) to give the macro-composite, this process is a bottom-up “hierarchical” advanced manufacturing process, and since the resulting nanocomposites will have “multifunctionality” with improve properties in various functional areas such as chemical and fire resistance, damping, stiffness, strength, fracture toughness, EMI shielding, and electrical and thermal conductivity, the resulting nanocomposites are in fact “multifunctional hierarchical nanocomposites.” In this paper, the current state of knowledge in processing, performance, and characterization of these materials are addressed.

Topics: Nanocomposites
Commentary by Dr. Valentin Fuster
2013;():V009T10A027. doi:10.1115/IMECE2013-65664.

Natural fiber as a reinforcing constituent can play a dominant role in the field of fiber reinforced polymer composites (FRPC) due to its eco-friendliness, renewability, abundance in nature, co2-neutrality, flexibility, low density, and low cost. Hence, sugarcane fiber can be a potential candidate to replace the synthetic FRPC. The objective of this study is to evaluate the effect of chemical treatment on the tensile properties of single sugarcane fiber. Sugarcane collected from the local market was cut into some specific length and fibers were extracted from the juicy section. These fibers were then dried in an oven to remove the moisture. Surface modification was accomplished by performing alkali treatment and neutralizing by acetic acid solution. The fiber was then rinsed with water and dried at 80°C for about twenty four hours using an oven. Untreated and treated fibers were characterized using tensile testing according to the ASTM D 3822-01 standard. Optical microscopy (OM) was employed to measure the diameter of the fiber and scanning electron microscopy (SEM) was used to evaluate the fracture morphology of failed samples. Tensile tests were carried out on the span length of 25 mm of the single fiber. The resultant data showed that maximum improvement in the tensile strength and modulus was observed to be 87% and 29%, respectively, compared to those of untreated ones due to chemical treatments using 5% NaOH solution and 2% acetic acid solution, respectively. Strain to maximum strength was enhanced by about 16% compared to that of the untreated one. A small initial weight loss was observed in the temperature ranging from 25 to 150 °C due to the evaporation of water. However, untreated fiber started to decompose at around 200 °C while treated fiber started to become decomposed at around 250°C. It might be due to the removal of non-cellulosic substances including hemicellulose, lignin, and pectin as a result of the chemical treatment. Fracture morphology of the treated fiber revealed rougher fracture surfaces compared to untreated fiber surfaces. This is an indication of more energy absorption by the treated fibers during the tensile loading.

Topics: Fibers
Commentary by Dr. Valentin Fuster
2013;():V009T10A028. doi:10.1115/IMECE2013-66146.

The strain energy present in the structure due to manufacturing imperfections as initial strains are considered and the method for investigating the effects of strain energy due to manufacturing imperfections is developed. The strain energy restored in the structures produced by the initial strains is optimised to find the worst case set of imperfections. The methods proposed are validated by applying to one freedom truss structure. Then the case of a truss is considered with the worst set of imperfections for strain energy, peak force value and work input determined. The worst case set of imperfections contributes maximum strain energy in the truss with different configuration angles is found and driving force values and work input due to presence of changing strain energy through deployment are determined, the worst case set of imperfections are also found by optimisation of these quantities. The methods developed in this paper can be extended to all planar deployable truss structures.

Commentary by Dr. Valentin Fuster
2013;():V009T10A029. doi:10.1115/IMECE2013-66679.

Recent years, thermoplastics incorporated with particulate fillers have been gained high interests. To improve the mechanical properties of the natural particle reinforced polymer plastics, hybrid structure has been applied on the composite combining natural particle with stronger synthetic fibers. However, the reinforcing mechanism of the hybrid composite is quite complicated. Experiments on it may become time consuming and cost prohibitive. Therefore, researchers are interested in studying variable models to predict the elastic properties of the composites.

In this study, glass short fiber/wood particle/pp hybrid composites were prepared by injection molding process at a fixed reinforcement to matrix ratio of 51:49. 4 kinds of hybrid specimens with glass fiber/wood particle ratios of 41:10, 31:20, 21:30 and 11:40 were fabricated. The effect of hybridization content on the mechanical properties of the composites was evaluated based on tensile test. Theoretically, the elastic modulus of hybrid composites was predicted by using the rule of hybrid mixtures (RoHM) equation and classical lamination theory (CLT) and the accuracy of the two estimation models has been discussed.

Results showed that it can be considered the hybridization of wood powder into glass/PP composite could contribute to a similar high elastic modulus with high green degree. On the other hand, the fiber orientation factor, fiber length distribution factor, powder dispersion factor were very important factors and need to be considered in the prediction model.

Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures and Fluids: High Strain-Rate Phenomena: Modeling and Experiment

2013;():V009T10A030. doi:10.1115/IMECE2013-62283.

Three energy absorption mechanisms of severe dynamic loading events are numerically investigated using a finite element model of a cross-ply unidirectional (UD) composite laminate. In this study, the inelastic energy absorption mechanisms associated with damage at the interfacial and constituent levels were numerically characterized through three admissible failure modes: fiber breakage, matrix shearing, and fiber/matrix debonding (delamination) (i.e., cohesive failure). The UD composite was constructed of ultrahigh molecular weight polyethylene (UHMWPE) fibers separately reinforced with a rigid (epoxy) matrix material. The energy absorption capacities of these damage mechanisms were contrasted for three different dynamic loading cases including blast, shock, and ballistic impact at three different energy levels. Energy loss due to cohesive failure was observed in all three loading cases and energy levels. Furthermore, energy loss due to matrix failure was observed at all energy levels for the blast case, but only for the highest energy level in the shock and ballistics. There was energy loss due to fiber failure in the blast and in the highest energy ballistics impact case. However, there wasn’t any fiber damage in the shock case.

Commentary by Dr. Valentin Fuster
2013;():V009T10A031. doi:10.1115/IMECE2013-63522.

This paper addresses three-dimensional dynamic finite element analysis and validations for strain-rate dependent elastic-plastic sandwich steel plate with various corrugated core arrangements subjected to dynamic air pressure loads. The sandwich steel plate consists of top and bottom flat substrates of Steel 1018 and corrugated core layers of Steel 1008. The developed model is validated with a set of shock tube experiments. Various corrugated core arrangements are taken into consideration for optimizing core design parameters in order to maximize mitigation of blast load effects onto the structure.

Commentary by Dr. Valentin Fuster
2013;():V009T10A032. doi:10.1115/IMECE2013-64770.

The increasing social pressure for biodegradable, sustainable, and environmentally-friendly products has launched the use of natural fibers in fiber reinforced polymer composites. Unfortunately, due to the integration of organic material in thermoplastic components, the fiber-matrix interfacial bonding is poor. While the organic material is hydrophilic, able to absorb water, the majority of polymer matrices are hydrophobic, unable to bond with water. The interfacial shear strength, a quantity to measure this bonding, has been shown to be improved through morphological and chemical treatment. In this context, the interfacial shear strength of banana fiber in low-density polyethylene has not been fully characterized. The aim of this study is to identify and optimize the interfacial shear strength of banana fiber in a polymer matrix through a polymer-compatibilization technique. For characterization of the fiber-matrix interfacial bonding, a commonly used micromechanical technique, the pull-out test, is used. While these initial results range from 0.4 MPa to 1.5 MPa, multiple samples exhibit greater than 30% improvement in interfacial bonding. The results reveal a need for a more exact measurement method; however, they also reveal the potential use of polymer-compatibilization as a replacement to fiber-modification treatments.

Commentary by Dr. Valentin Fuster
2013;():V009T10A033. doi:10.1115/IMECE2013-65642.

Global and local microstructural weak links for spall damage were investigated using 3-D characterization in polycrystalline (PC) and multicrystalline (MC) copper samples, respectively. All samples were shocked via flyer-target plate experiments using a laser drive at low pressures (2–6 GPa). The flyer plates measured approximately 500 μm thick and 8 mm in diameter and the target plates measured approximately 1000 μm thick and 10 mm in diameter. Electron Backscattering Diffraction (EBSD) and optical microscopy were used to determine to presence of voids and relate them to the surrounding microstructure. Statistics on the strength of grain boundaries (GBs) was conducted by analyzing PC samples and collecting the misorientation across GBs with damage present, and it was found that a misorientation range of 25–50° is favorable for damage. Statistics were also taken of copper PC samples that had undergone different heat treatments and it was found that although the 25–50° range is less dominant, it is still favorable for damage nucleation. Removal of initial plastic strain via heat treatments and an increase in Σ3 CSL boundaries, indicative of strong annealing twins, also led to an increased amount of transgranular damage. 3-D X-ray tomography data were used to investigate the shape of the voids present in untreated, as received and heat treated samples. It was found that the as received sample contained a higher amount of “disk”, or, “sheet-like” voids indicative of intergranular damage, whereas the heat treated samples had a higher fraction of spherical shaped voids, indicative of transgranular damage. MC samples were used to study microstructural weak links for spall damage because the overall grain size is much larger than the average void size, making it possible to determine which GBs nucleated damage. Simulations and experimental analysis of damage sites with large volumes indicate that high Taylor factor mismatches with respect to the crystallographic grain GB normal is the primary cause for the nucleation of damage at a GB interface and a low Taylor factor along the shock direction in either grain drives void growth perpendicular to the GB. Cases where experimental results show damage and simulation results show no damage are attributed to the presence of an intrinsic microstructural weak link, such as an incoherent twin boundary.

Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures and Fluids: Hybrid Multifunctional Composite Materials

2013;():V009T10A034. doi:10.1115/IMECE2013-62251.

Carbon fiber reinforced polymer composites (CFRPs) are renowned for their superior in-plane mechanical properties. However, they lack sufficient out-of-plane performance. Integrating carbon nanotubes (CNTs) into structures of CFRPs can enhance their poor out-of-plane properties. The present work investigates the effect of adding CNTs, grown on carbon fibers via a relatively low temperature growth technique, on the on and off-axis tensile properties as well as on transverse high velocity impact (∼100 m.s−1) energy absorption of the corresponding CFRPs. Two sets of composite samples based on carbon fabrics with surface grown CNTs and reference fabrics were fabricated and mechanically characterized via tension and impact tests. The on-axis and off-axis tests confirmed improvements in the strength and stiffness of the hybrid samples over the reference ones. A gas gun equipped with a high-speed camera was utilized to evaluate the impact energy absorption of the composite systems subjected to transverse spherical projectiles. Due to the integration of CNTs, intermediate improvements in the tensile properties of the CFRP were achieved. However, the CFRPs’ impact energy absorption was improved significantly.

Commentary by Dr. Valentin Fuster
2013;():V009T10A035. doi:10.1115/IMECE2013-63071.

This article deals with the multi objective optimization of square hybrid tubes (metal-composite) under axial impact load. Maximum crushing load and absorbed energy are objective functions and fiber orientation angles of the composite layers are chosen as design parameters while the maximum crush load is limited. Back-propagation artificial neural networks (ANNs) are utilized to construct the mapping between the variables and the objectives. Non-dominated sorting Genetic algorithm–II (NSGAII) is applied to obtain the optimal solutions and the finite element commercial software LS-DYNA is used to generate the training and test sets for the ANNs. Optimum results are presented as a Pareto frontier.

Commentary by Dr. Valentin Fuster
2013;():V009T10A036. doi:10.1115/IMECE2013-63326.

The inclusion of nanomaterials within fiber reinforced plastics (FRPs) could improve their resistance against time dependent deformation. Conceivable high temperature applications of such hybrid composites make it crucial to investigate their temperature-dependent properties as well as their durability. In this study, zinc oxide (ZnO) nano rods were grown on the surface of carbon fibers and the hybridized reinforcement was formed in a laminate composites. The viscoelastic behavior was probed utilizing dynamic mechanical analysis (DMA). The time/temperature superposition principle (TTSP) was invoked to obtain the viscoelastic properties of FRPs based on fibers with different surface treatments. Results indicated that the presence of ZnO nano rods at the interface between the carbon fibers and the epoxy matrix enhances the composite’s creep resistance at elevated temperatures and prolonged duration.

Commentary by Dr. Valentin Fuster
2013;():V009T10A037. doi:10.1115/IMECE2013-65791.

The use of zinc oxide (ZnO) nanostructures with fiber reinforced polymer composites has gained more applications recently due to the additive benefits of the semi-conductivity and piezoelectricity of ZnO. In this study, we suggest growing ZnO nanowires (NWs) on the surface of woven carbon fibers using low temperature (c.a. 80°C) hydrothermal technique and integrating the modified fibers in composite structures based on epoxy matrix. Mechanical vibrations tests based on samples with and without surface-grown ZnO established the enhanced damping of the hybrid composite structures through measuring the damping ratio and the vibration amplitude. We hypothesize that, besides the piezoelectric induced damping, the large aspect ratio of ZnO nanowires could provide higher interfacial friction with the epoxy matrix and in between the neighboring nanowires which in return could provide more energy dissipation.

Commentary by Dr. Valentin Fuster
2013;():V009T10A038. doi:10.1115/IMECE2013-66509.

Vertically aligned arrays of zinc oxide nanowires can serve as an adjustable interface for fiber composites through controllable synthesis techniques. When grown on carbon fiber surfaces as a fiber-matrix interphase of a composite, ZnO nanowires increase the surface area of interaction between fiber and matrix, and thus cause a greater interfacial shear strength of the composite. The ability to control the interfacial strength of this interphase through tailored morphologies enables the design of composite systems to specific applications. This report focuses on the controlled growth of ZnO nanowires and correlates the relationship between nanowire length and interfacial shear strength of the composite. Previous studies have focused on the effects of nanowire morphology on the interfacial strength; however, the data was limited to nanowire lengths < 1μm due to problems with nanowire uniformity and cleanliness [1]. Here, a new synthesis method is applied to the growth of zinc oxide nanowires on carbon fiber that enables the production of long, vertically aligned, uniform nanowires while maintaining the tensile properties of the fiber. The nanowires created by the new method are then compared to previous method nanowires by scanning electron microscopy imaging. Lastly, the interfacial shear strength of the fiber/polymer matrix composite is tested using single fiber fragmentation and correlated to the nanowire length of each method.

Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures and Fluids: Materials and Meta-Materials at Varying Length Scales and Frequency Ranges

2013;():V009T10A039. doi:10.1115/IMECE2013-63992.

In this paper, effects of friction coefficient and tool geometry on the thickness variations of a cylindrical cup were studied. Blank is made of SPXI250 alloy sheet which was analyzed by Finite Element Method (FEM). This not been studied yet. Finite Element modeling of the deep drawing process was conducted using ABAQUS/EXPLICIT software. A set of appropriate die and punch were designed for experimental tests. The results of the simulation showed that a change in the friction coefficient of the die-blank interface leads to a significant changes in the cup thickness. Moreover, the results revealed that the influence of die nose radius on the final cup thickness variations is greater than that of the punch nose radius. The simulation results of this study were compared with the experimental results and those of the other investigators’. The comparisons of the experimental and simulation results with those of the other researchers were so satisfactory.

Topics: Friction , Alloys , Geometry
Commentary by Dr. Valentin Fuster
2013;():V009T10A040. doi:10.1115/IMECE2013-65475.

The topology optimization method is extended to solve a single phase flow in porous media optimization problem based on the Two Point Flux Approximation model. In particular, this paper discusses both strong form and matrix form equations for the flow in porous media. The design variables and design objective are well defined for this topology optimization problem, which is based on the Solid Isotropic Material with Penalization approach. The optimization problem is solved by the Generalized Sequential Approximate Optimization algorithm iteratively. To show the effectiveness of the topology optimization in solving the single phase flow in porous media, the examples of two-dimensional grid cell TPFA model with impermeable regions as constrains are presented in the numerical example section.

Commentary by Dr. Valentin Fuster
2013;():V009T10A041. doi:10.1115/IMECE2013-65533.

Fluid droplet on a surface with roughness has been simulated to investigate the hydrophobicity of surface and also measure the increase in contact angle (CA). Surface roughness increases the area of solid-liquid interface and this increase in composite interface makes the water to repel solid surface, thus causing an increase of the CA. Recently heterogeneous structure surface, which is pillar or rib structures with gradually changing pitches in certain direction, has gained lot of interest from researchers because wetting characteristics of those structures allow droplet movement without external forces. In this paper, droplet movement for heterogeneous surface cases are simulated with the computational fluid dynamics (CFD) modeling, known as Lattice Boltzmann method (LBM). First part of the study concentrates on droplet transportation. Half of the surface is more-hydrophobic region, textured with microscopic pillars and the other part of surface is less-hydrophobic, textured or smooth surface. Second part of the study concentrates on droplet breakup. More-hydrophobic textured band is located at center of less-hydrophobic textured surface. To see the effect of surface structure only, we choose same chemical property for all surfaces. Water droplets are spatially placed on border line of the different textures of surface. The simulations are carried out using projection method of LBM. Projection method has been used to in this study to be able to model the large density difference between air and water. Two phase immiscible fluids flow consisting of air and water (density ratio of air to water = 1:1000) is built in 3D space by using Projection method. This method can calculate solid-liquid-gas composite interface.

Commentary by Dr. Valentin Fuster
2013;():V009T10A042. doi:10.1115/IMECE2013-66720.

A great need exists for vibration and noise control with thinner and smaller devices, especially at lower frequencies than those at which the usual magnetic and electrical metamaterials operate. Acoustic metamaterials have been under development for such purposes. Some of the present authors have experimentally and numerically investigated circular acoustic metamaterials made of lexan plate and silicon membranes. In this work, the authors extend the investigation to the use of some other materials and relative see if and how well such a construction may be utilized for meta-material applications.

Commentary by Dr. Valentin Fuster
2013;():V009T10A043. doi:10.1115/IMECE2013-66722.

Acrylonitrile-Butadine-Styrene (ABS) has been receiving much attention as a cushion against impact and vibration, on account of its very favorable mechanical properties, including elevated impact strength, stiffness and tensile strength, as well as outstanding formability. The geometry of deployed samples does influence dynamic performance. In this work, the methods of analysis, experiment and numerical computation have been applied to explore different modal parameters of rectangular ABS specimens with completely free boundary conditions. Experimentally, Pulse 15.1 software was used to investigate the modal parameters while the specimens were numerically modeled in Abaqus/Standard 3D using C3D20R (second order 20-node quadratic brick) element types with the Lancsoz Eigensolver method. Parametric explorations over the geometry space enabled useful trends to be identified with respect to vibration and impact applications. Experimental and numerical results were found to compare very favorably.

Topics: Vibration , Geometry
Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures and Fluids: Mechanics and Design of Cellular Materials

2013;():V009T10A044. doi:10.1115/IMECE2013-62113.

The work presented in this paper is a continuation of the study conducted on exploring impact properties of a functionally graded bio cellular structure found in a banana peel. The graded cellular structure with unfilled cells reacts intelligently to impact loading and crushes in a manner that results in a higher amount of energy absorption as compared to an equivalent regular honeycomb structure. In this paper, a non-Newtonian fluid is introduced into the cells of a regular honeycomb structure, and its effect on energy absorption properties are studied using an experimental approach. The results are compared with impact mitigation properties of an unfilled regular honeycomb structure. The introduction of non-Newtonian fluid significantly enhances the energy absorption capacity of regular honeycomb structure, and therefore, suggests that fluid inside a banana peel structure is playing a critical role in energy and impact absorption. A rudimentary relationship between the numbers of fluid filled layers and total energy absorption capacity of the structure is presented through a regression analysis.

Commentary by Dr. Valentin Fuster
2013;():V009T10A045. doi:10.1115/IMECE2013-63598.

In an effort to tailor functional materials with customized anisotropic properties — stiffness and yield strain, we propose porous materials consisting of flexible mesostructures designed from the deformation of a re-entrant auxetic honeycomb and compliant mechanisms. Using an analogy between compliant mechanisms and a cellular material’s deformation, we can tailor in-plane properties of mesostructures; low stiffness and high strain in one direction and high stiffness and low strain in the other direction. Two mesostructures based on hexagonal honeycombs with positive and negative cell angles are generated. An analytical model is developed to obtain effective moduli and yield strains of the porous materials by combining the kinematics of a rigid link mechanism and deformation of flexure hinges. A numerical technique is implemented to the analytical model for nonlinear constitutive relations of the mesostructures and their strain dependent Poisson’s ratios. A Finite Element Analysis (FEA) is used to validate the analytical and numerical model. The moduli and yield strain of a porous aluminum alloy are about 6.3GPa and 0.26% in one direction and about 2.8MPa and 12% in the other direction. The mesostructures have extremely high positive and negative Poisson’s ratios, Display Formulaνxy* (∼ ±40) due to the large rotation of the link member in the transverse direction caused by the input displacement in the longitudinal direction. The mesostructures also show higher moduli for compressive loading due to the contact of slit edges at the center region. This paper demonstrates that compliant mesostructures can be used for a next generation material design in terms of tailoring mechanical properties; moduli, strength, strain, and Poisson’s ratios. The proposed mesostructures can also be easily manufactured using a conventional cutting method.

Topics: Design
Commentary by Dr. Valentin Fuster
2013;():V009T10A046. doi:10.1115/IMECE2013-64190.

The mechanical behavior of 2-D periodic cellular materials is investigated using a continuum-based modeling approach. Two micromechanical models are developed on the basis of representative unit cell concept in which skeleton of cellular material is modeled as elastic beams. The ANSYS finite element code is used to solve the beam model of skeleton. Elastic moduli of square and triangular networks comprising the microstructure of the cellular material are calculated based on an equivalent continuum model. This is achieved by equating the stored energy in skeleton of a unit cell to the strain energy of the equivalent continuum under a set of prescribed boundary conditions. A proper displacement-controlled (essential) boundary condition generates a uniform strain field in both models which corresponds to calculation of one elastic modulus at a time. Then, effective Young’s modulus and Poisson’s ratio of continuum are extracted from the calculated elastic moduli. The dependence of effective elastic constants on relative density and thickness to length ratio of the microstructure is investigated. Furthermore, the in-plane behavior of cellular solids in compression is explored with the help of current modeling. The proposed models may contribute to optimal designs of a new class of materials with tailored geometry and material properties which could be useful in a broad range of structural applications.

Topics: Modeling
Commentary by Dr. Valentin Fuster
2013;():V009T10A047. doi:10.1115/IMECE2013-64914.

Cellular materials have a high strength-to-weight ratio, which is good for lightweight structural applications. In order to accelerate the commercial use of cellular materials in the structural applications, a well understanding of fracture behavior of cellular materials is required in terms of structural integrity. The objective of the study is to develop a predictive model on fracture behavior of orthotropic cellular polymers, prepared from an additive manufacturing method, under the mode-I macroscopic loading. The constituent material’s fracture properties are obtained from the three-point bending test of samples with a notched crack. Using the base material’s properties, a model on fracture toughness of hexagonal honeycombs with a varying cell angle is developed using a linear elastic fracture mechanics (LEFM) model of a cell wall material. Numerical and experimental tests will follow to validate the model.

Commentary by Dr. Valentin Fuster
2013;():V009T10A048. doi:10.1115/IMECE2013-65101.

Wood, due to its biological origin, has the capacity to interact with water. Sorption/desorption of moisture is accompanied with swelling/shrinkage and softening/hardening of its stiffness. The correct prediction of the behavior of wood components undergoing environmental loading or industrial process requires that the hygric, thermal and mechanical (HTM) behavior of wood are considered in a coupled manner. In addition, we propose a comprehensive framework using a fully coupled poromechanical approach, where its multiscale implementation provides the capacity to take into account, directly, the exact geometry of wood cellular structure, using computational homogenization. A hierarchical model is used to take into account the subcellular composite-like organization of the material. Such advanced modeling requires high resolution experimental data for the appropriate determination of inputs and for its validation.

Topics: Wood products , Water
Commentary by Dr. Valentin Fuster
2013;():V009T10A049. doi:10.1115/IMECE2013-66684.

Recycled paper is helpful to reduce trash discharge, save resource and cost. Recycled paper tube is one of the most successful cases in application of recycled paper. It is an excellent choice for packing. It’s also used in the construction of temporary structures for both exhibition spaces or for rapid-recovery shelters in emergency operations. As paper tubes are laminated composite materials composited of paperboard which is inherent anisotropy materials, the research on mechanical property and fracture behavior becomes more complicated. In order to analyze deformation and fracture behavior of paper tubes under lateral compressive load, six types of paper tube fabricated with different kinds of paperboard and number of ply were examined in this study. The six types included three different kinds of paperboard. Cracks propagation was observed through lateral compression test process. At the same time, energy absorption in elastic stage was discussed between different paper tubes.

Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures and Fluids: Mechanics in Biology and Medicine

2013;():V009T10A050. doi:10.1115/IMECE2013-63229.

Heart valves are inhomogeneous microstructure with nonlinear anisotropic properties and constantly experience different stress states during cardiac cycles. However, how tissue-level mechanical forces can translate into altered cellular stress states remains unclear, and associated biomechanical regulation in the tissue has not been fully understood. In the current study, we use an image-based finite element method to investigate factors contributing the stress distributions at both tissue- and cell-levels inside the healthy heart valve tissues. Effects of tissue microstructure, inhomogeneity, and anisotropic material property at different diastole states are discussed to provide a better understanding of structure-mechanics-property interactions, which alters tissue-to-cell stress transfer mechanisms in heart valve tissue. To the best of the authors’ knowledge, this is the first study reporting on the evolution of stress fields at both the tissue- and cellular-levels in valvular tissue, and thus contributes toward refining our collective understanding of valvular tissue micromechanics while providing a computational tool enabling further study of valvular cell-tissue interactions.

Commentary by Dr. Valentin Fuster
2013;():V009T10A051. doi:10.1115/IMECE2013-63534.

Over the last several decades investigations of replacement material for intervertebral disc (IVD) have been an important topic in medical research. The challenge is to create materials whose mechanical behavior ideally matches that of the articular cartilage comprising the native discs. Thus, the study of articular cartilages underlying mechanical characteristics is a key issue for the successful development and refinement of replacement materials.

Using both experimental and cartilage histostructural data, including fiber orientation, a visco-hyperelastic-diffusion (VHD) material model is developed and implemented. This allows us to numerically study the mechanical behavior of an IVD consisting of a cartilaginous ring surrounding a fluid core.

In this work, a three dimensional finite element (FE) model is developed to simulate the behavior of an IVD under various loading conditions. Finally, model parameters are iteratively determined by comparing the simulation results to compression tests on corresponding discs performed in a MTS machine with a tempered nutrient solution.

Commentary by Dr. Valentin Fuster
2013;():V009T10A052. doi:10.1115/IMECE2013-63829.

Skin is a multilayered composite material and composed principally of the proteins collagen, elastic fibers, and fibroblasts. The direction-dependent material properties of skin tissue is important for physiological functions like skin expansion. The current study has developed methods to characterize the directional biomechanical properties of porcine skin tissues. It is observed that skin tissue has a nonlinear anisotropy biomechanical behavior, where the parameters of material stiffness is 378 ±160 kPa in the preferred-fiber direction and 65.96±40.49 kPa in the cross-fiber direction when stretching above 30% strain equibiaxially. The results from the current study will help optimize functional skin stretching for patients requiring large surface area skin grafts and reconstructions due to burns or other injuries.

Commentary by Dr. Valentin Fuster
2013;():V009T10A053. doi:10.1115/IMECE2013-64498.

For medical applications, it is desirable to cultivate tendon cells. In addition to the many biochemical requirements for successful cultivation, mechanical stimulation also plays an important role. Especially, it is well known that tendon cells de-differentiate quickly if they are not put under physiological conditions. For this reason, a new bioreactor for the investigation and cultivation of tenocytes is developed, in which tenocytes are seeded on a carrier material. To be able to identify the real loads the tenocytes are subjected to, the material properties of the carrier material are found by performing material tests followed by a numerical analysis.

Topics: Modeling , Bioreactors
Commentary by Dr. Valentin Fuster
2013;():V009T10A054. doi:10.1115/IMECE2013-66383.

An axisymmetric model of an intracranial saccular aneurysm is presented and analyzed. The model assumes a simplified spherical geometry for the aneurysm in order to develop insight into the mechanisms that effect wall shear stress and deformation of the membrane. A theoretical model is first developed based on Stokes’ equations for viscous flow in order to derive a stream function that describes vortical flow inside a sphere representative of flow inside a real aneurysm. This flow pattern is implemented in a finite element model of a spherical aneurysm using the software COMSOL Multiphysics. The results indicate close agreement between the theoretical and computational models in terms of the flow streamlines and location of the maximum wall shear stress. Furthermore, the computational model accounts for the deformation and stress of the membrane, showing regions of maximum tension and compression at opposite poles of the saccular membrane. This work elucidates many important results regarding the mechanics of saccular aneurysms and provides a basis for developing more physiologically realistic analyses.

Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures and Fluids: Mechanics of Soft Materials

2013;():V009T10A055. doi:10.1115/IMECE2013-63839.

Rapid deployment and mobility of lightweight structures, namely inflatable structures, are of growing significance to the military and space communities. When deployment and rigidity are driven by pressure (for example, air or fluid) and materials such as textiles, elastomers and flexible composites are used, significant load carrying capacity per unit weight (or per-unit stowed volume) can be uniquely achieved. Specifically, the pressurized air directly provides the stiffness to support structural loads, thus eliminating the requirement for heavy metal stiffeners that are used in conventional rigid structures. However, the material and system behaviors are not sufficiently understood. Furthermore, predictive-performance analysis methods and test standards are not adequately established because the behaviors of inflatable fabric structures often involve coupled effects from inflation pressure such as fluid-structure interactions (FSI’s), thermo-mechanical coupling and nonlinear constitutive responses of the materials. These effects can restrict the use of conventional design, analysis and test methods.

This research explores the mechanics of air-inflated drop-stitch fabric panels subject to bending loads using analytical and experimental methods. Results of experimental four-point bend tests conducted at various inflation pressures are used to validate the analytical method. The predicted and experimental deflections, wrinkling onset moments, ultimate loads, pressure changes, etc. are compared and discussed.

Commentary by Dr. Valentin Fuster
2013;():V009T10A056. doi:10.1115/IMECE2013-64014.

Polymer composite structures are usually subjected to large flexural loadings during their life-span of the structures, so the flexural behavior of these structures and their constituents in different environmental conditions are critical to their use. A novel analytical approach for epoxy resin semi-brittle materials with strain softening model in tension and compression has been developed to investigate the flexural behavior of these materials. The value of the flexural over-strength factor which is the ratio of the flexural strength to the strength obtained from tension and compression stress strain models depends on stress gradient, size and loading system and it has already been evaluated at the laboratory condition. The mechanical properties of epoxy resin materials are sensitive to environmental effects at which they are loaded. The influence of temperature 60°C and humidity 90% Rh on tension, compression and flexural behavior of epoxy resin polymeric materials PRI and PR 520 have been investigated. Digital image correlation system was used for material characterization. The effects of heat and humidity on softening localization in flexural response were considered. The influence of heat and humidity on the flexural over-strength factor was evaluated.

Topics: Epoxy resins
Commentary by Dr. Valentin Fuster
2013;():V009T10A057. doi:10.1115/IMECE2013-64344.

In the last ten years, a new type of advanced polymer known as swelling elastomer has been extensively used as sealing element in the oil and gas industry. These elastomers have been instrumental in various new applications such as water shutoff, zonal isolation, sidetracking, etc. Though swell packers can significantly reduce costs and increase productivity, their failure can lead to serious losses. Integrity and reliability of swelling-elastomer seals under different field conditions is therefore a major concern. Investigation of changes in material behavior over a specified swelling period is a necessary first step for performance evaluation of elastomer seals. Current study is based on experimental and numerical analysis of changes in compressive and bulk behavior of an elastomeric material due to swelling. Tests and simulations were carried out before and after various stages of swelling. Specimens were placed in saline water (0.6% and 12% concentration) at a temperature of 50°C, total swelling period being one month. Both compression and bulk tests were conducted using disc samples. A small test rig had to be designed and constructed for determination of bulk modulus. Young’s modulus (under compression) and bulk modulus were determined for specimens subjected to different swelling periods. Shear modulus and Poisson’s ratio were calculated using isotropic relations. Experiments were also simulated using the commercial finite element software ABAQUS. Different hyperelastic material models were examined. As Ogden model with second strain energy potential gave the closest results, it has been used for all simulations.

The elastomer was a fast-swell type. There were drastic changes in material properties within one day of swelling, under both low and high salinity water. Values of elastic and shear modulus dropped by more than 90% in the first few days, and then remained almost constant during the rest of the one-month period. Poisson’s ratio, as expected, showed a mirror behavior of a sharp increase in the first few days. Bulk modulus exhibited a fluctuating pattern; rapid initial decrease, then a slightly slower increase, followed by a much slower decrease. Salinity shows some notable effect in the first 5 or 6 days, but has almost no influence in the later days. Very interestingly, Poisson’s ratio approaches the limiting value of 0.5 within the first 10 days of swelling, justifying the assumption of incompressibility used in most analytical and numerical models. In general, simulations results are in good agreement with experimental ones.

Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures and Fluids: Modeling of Multifunctional Materials

2013;():V009T10A058. doi:10.1115/IMECE2013-66451.

A non-linear theoretical model including bending and longitudinal vibration effects was developed for predicting the magneto electric (ME) effects in a laminate bar composite structure consisting of magnetostrictive and piezoelectric multi-layers. If the magnitude of the applied field increases, the deflection rapidly increases and the difference between experimental results and linear predictions becomes large. However, the nonlinear predictions based on the present model well agree with the experimental results within a wide range of applied electric field. The results of the analysis are believed to be useful for materials selection and actuator structure design of actuator in actuator fabrication. It is shown that the problem for bars of symmetrical structure is not divided into a plane problem and a bending problem. A way of simplifying the solution of the problem is found by an asymptotic method. After solving the problem for a laminated bar, formula that enable one to change from one-dimensional required quantities to three dimensional quantities are obtained. The derived analytical expression for ME coefficients depend on vibration frequency and other geometrical and physical parameters of laminated composites. Parametric studies are presented to evaluate the influences of material properties and geometries on strain distribution and the ME coefficient. Analytical expressions indicate that the vibration frequency strongly influences the strain distribution in the laminates, and that these effects strongly influence the ME coefficients. It is shown that for certain values of vibration frequency (resonance frequency), the ME coefficient becomes infinity; as a particular case, low frequency ME coefficient were derived as well.

Commentary by Dr. Valentin Fuster
2013;():V009T10A059. doi:10.1115/IMECE2013-66763.

Micro-electromechanical system (MEMS) is considered as the most promising technology for the development of sensors. MEMS based fingerprint sensors are used in modern day biometrics. They are generally realized using piezo resistive sensing technology in lieu of other technologies because of easy and low cost micro fabrication processes involved. But, such sensors can fail due to a number of stresses developed as it is pressed. In this paper, the first investigation is pertaining to the failure of MEMS based piezoresitive fingerprint sensors. The results indicate the sensors’ ability to withstand the maximum finger pressure. In the second investigation, the sensitivity analysis is performed using open source software, Quite Universal Circuit Simulator (QUCS) and the results are also compared with that obtained from solid mechanical simulation using COMSOL Multiphysics. The final investigation is to evaluate electrical performance of sensors connected in different configurations in circuits.

Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures and Fluids: Multi-Field Studies in Heterogeneous Materials: Experimental, Theoretical and Numerical Approaches

2013;():V009T10A060. doi:10.1115/IMECE2013-63282.

Finite element models are increasingly being utilized in composite materials design; thus, an increase in the accuracy of the model analysis and a decrease in computational cost are of paramount importance. This study investigates the effects of a particular add-on, Helius:MCT (Firehole Technologies, Inc.), onto the Abaqus (Dassault Systèmes) software package. Unlike the stand-alone Abaqus software, Helius:MCT embodies a solver, which analyzes the composite structure by separating the fiber and matrix into constituent parts. Treating the fiber and matrix as separate, yet linked entities, allows for a more accurate depiction of the formations of stress and strain within the composite. Furthermore, Helius:MCT utilizes a method called Intelligent Discrete Softening (IDS), a feature not present within Abaqus, to increase solver robustness and convergence probability. An Abaqus finite element (FE) model of a notched, carbon-fiber panel loaded in bending was used in this study. Six different laminate combinations were tested with six variations of the Abaqus model. Three of the variations used Helius:MCT with Abaqus and three the stand-alone Abaqus package. The combinations were composed of either 20 or 40 plies with 10, 30, or 50 percent all zero ply orientations. All the FE analysis results were compared to experimental values for a plate of the exact configuration as that of the model. The most accurate results were obtained using Helius:MCT. The configuration with the greatest accuracy utilizes Helius:MCT and deviates an average of 1.7 percent from experimental values for maximum flexural strength. A single run takes an average of 7 hours to complete. Conversely, the most accurate configuration obtained without the use of Helius:MCT deviates an average of 10 percent from the experimental values and takes over 80 hours to run. Helius: MCT increases the accuracy and decreases the computational costs of the analyses of composite models in Abaqus. The improvements in analyses while using Helius: MCT may allow for a substantial savings in experimental costs and in valuable time.

Commentary by Dr. Valentin Fuster
2013;():V009T10A061. doi:10.1115/IMECE2013-63736.

Polyurea is an elastomer that has been intensively researched due to its excellent thermal and mechanical properties. Polyurea based composite material has recently become a research interest to further explore what this polymer has to offer. In order to better understand the overall static or dynamic mechanical properties of the polyurea based composites, how to tailor and characterize the polyurea-filler interface has become a crucial problem. This study focuses on one of the filler materials, glass. Three types of polyurea-glass interfaces are studied by using silane reagents that have similar molecular structures but with different end functional groups to modify the glass surfaces. Accordingly, bonds with different strengths are formed between the glass and the polyurea through the different chemical character of the reagent molecules. The polyurea-glass interfacial properties are tested by the single-fiber fragmentation, which is a widely used method to test the shear properties of the interface between the fiber and the polymer. Single-fiber fragmentation samples are fabricated by casting a single glass fiber along the axial direction of the dogbone-shaped polyurea tension test sample. Tension tests are conducted and the continuous photoelastic videos are taken to observe the single fiber fragmentation process until the fragmentation reaches its saturation state. Meanwhile, stress-strain data are recorded. By analyzing the single-fiber fragmentation data, the polyurea-glass interfacial shear strengths are calculated. The observation of the debonding zones at the interface is used to find the approximate models for the interfacial shear adhesion of polyurea-glass interfaces for different reagents, hence proving the potential for tailoring of the interfacial strength using surface treatment.

Topics: Glass , Fibers
Commentary by Dr. Valentin Fuster
2013;():V009T10A062. doi:10.1115/IMECE2013-63993.

This research explores the structural properties of fresh concrete. The work is relevant wherever green, or uncured, concrete must be load-bearing. In traditional concreting, rigid forms mold and protect young concrete, and these forms are not removed until the maturing material has developed considerable load-bearing strength. Conversely, an automated construction technology under development at the University of Southern California, proposes to rapidly fabricate civil structures additively — layering continuous ribbons of fresh unconfined concrete — the freshly layered concrete must be load-bearing immediately upon placement. This is an unprecedented structural requirement, and little has been done to substantiate uncured concrete in such a load-bearing capacity. With emphasis on expedient experimental techniques, early maturity, and time-dependent constitutive modeling, this research develops the engineering necessary to erect these structures safely.

Commentary by Dr. Valentin Fuster
2013;():V009T10A063. doi:10.1115/IMECE2013-66344.

Advances in materials characterization at the submicron and the nano-scales have progressed in the last decade. At the same time, computational capability for finite element analyses are also improving through technological developments in parallel computing. However, large computational models of nanostructured materials are currently limited by the lack of validation data. The work reported in this paper describes the formulation of a representative nanoscale model for Kevlar fibers based on failure section imaging that captures its fibril and microfibril structure. In this regard, a finite element model that captures the nanoscale structure of Kevlar fibers was developed to predict their macroscale response. Experimental derivation of geometrical parameters and physical properties of fibrils and microfibrils is challenging due to the sensitive nature of polymers. There are several microfibril parameters that reflect into effective fiber response, such as the microfibril constitutive behavior, length, diameter, shape, the inter-fibril shear and normal strength, and the inter-fibril normal and tangential force decay the after peak strength is achieved. This paper investigates the effect of each of the aforementioned parameters on the initial modulus, yield strength, ultimate strength, and strain rate dependence of Kevlar fibers with 10 μm average diameter. The sensitivity of the macroscale response to each microfibril parameter can be used to identify areas where experimental information can further enable the predictive capability of the computational model. A parametric study was performed to calculate the effective macroscale fiber response. Subsequently, a local gradient sensitivity method was employed to plot the sensitivity of the fiber response to each microfibril parameter.

Topics: Fibers , Failure
Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures and Fluids: Multi-Functional and Micro/Nano-Structured Materials — Modeling and Characterization

2013;():V009T10A064. doi:10.1115/IMECE2013-62427.

In a truly multiscale analysis of multilayered composites, the underlying phenomena are represented and their effect on the overall behavior is determined considering the interaction between the different phases and between the laminas. The analysis gets more involved when multiple phenomena are considered since in this case not only the direct effects play a role but also the coupled effects contribute to the distribution of the local fields and the overall response. In a fibrous composite laminate reinforced with piezoelectric filaments, for example, passing an electric field in the fibers generates stresses and strains which propagate through the composite medium due to constraints that exist both at the micromechanical, ply level, and the macromechanical, laminate level. Pyroelectricity is another coupling phenomenon in which a temperature change is caused by an electric field, and hence leads to changes in the stress and strain fields throughout the composite medium.

The above phenomena have been considered by the authors in a unified, transformation field analysis (TFA) approach in which stresses and strains which cannot be removed by mechanical unloading are treated as transformation fields. Due to mutual constraints of the phases and the bonded plies, local transformations generate stresses at the micro and macro levels, which are computed by means of influence functions which depend on material geometry and properties. Treatment of damage follows the same scheme but the transformation fields are instead determined such that the local stresses in the affected phase are removed.

In the present paper, implementation of the TFA approach in a general purpose finite element code is described. This expands the multiscale analysis outlined above to composite structures where complex geometries can be modeled and the effect of local phenomena can be considered. This naturally comes at a much larger cost of the computations compared to finite element analysis with homogenized models but the benefit of obtaining a more realistic response is clear. Moreover, the availability of high performance computing and parallel processing overcomes the computation time barrier. In the present paper however, simple examples of laminated structures are given as proof of concept in which the results are compared to those of standalone routines. Since the TFA approach centers on treating the composite medium as elastic with induced local transformations, implementation in the finite element framework does not require generation of an overall instantaneous stiffness matrix, which saves tremendously on the computation time. Instead, overall transformation strains, or stresses, are computed through a multiscale model, which is implemented as a user routine, and treated in the general finite element solution as nonmechanical strains in the same way thermal strains are treated.

Commentary by Dr. Valentin Fuster
2013;():V009T10A065. doi:10.1115/IMECE2013-62602.

In this study the effect of the temperature on the electrical conductivity of nanocomposites with carbon nanotube (CNT) fillers was investigated. A three-dimensional continuum Monte Carlo model was developed and employed first to form a CNT percolation network. CNT fillers were randomly generated and dispersed in a cubic representative volume element. Periodic boundary conditions were applied in this model to minimize size effects while decreasing computational cost. CNT fibers that connected electrically to each other through electron hopping were recognized and grouped as clusters. In addition to tunneling resistance, the effect of intrinsic CNT resistivity was considered. A three-dimensional resistor network was subsequently developed to evaluate nanocomposite electrical properties. Modeling employing the finite element method was conducted to evaluate the electrical conductivity of the percolation network. Considering the determining role of tunneling resistance on electrical conductivity of CNT based nanocomposites, as well as results obtained from experimental studies, temperature was expected to play an important role in nanocomposite electrical properties. The effect of temperature on electrical conductivity of CNT nanocomposites was thus investigated through employing the developed Monte Carlo and finite element models. Other aspects, including the electrical behavior of the polymer, tunneling resistivity and the intrinsic resistivity of CNT were considered in this study as well. The comprehensiveness of the developed modeling approach enables an evaluation of results in conjunction with experimental data in future works.

Commentary by Dr. Valentin Fuster
2013;():V009T10A066. doi:10.1115/IMECE2013-63744.

Ceramic materials have been used extensively in different industries due to their excellent properties in high temperature environment. Thermally sprayed ceramic coatings offer outstanding properties which make them suitable candidate for advanced applications. These coatings exhibit excellent wear resistant properties with high adhesion strength. Depending on the application, ceramic coatings can be subjected to in-plane or out-of-plane loading during service. When the components are exposed to extreme change in temperature, consistent expansion, and shrinkage of the materials will cause crack initiation and propagation, resulting in spallation of the coating and consequently failure of the components. In this study, mechanical performance of plasma sprayed Yttrium stabilized Zirconia coating was investigated. A powder mixture of Yttrium stabilized Zirconia (ZrO2−8Y2O3) was air plasma sprayed on a cast iron substrate. Microstructural characterization of the as-sprayed coating was performed to evaluate the microstructural uniformity of the deposited samples using scanning electron microscopy (SEM). Three-point bend tests were performed to measure bending modulus of the free standing as-sprayed coating samples. Knoop indentation technique was also used as an alternate method to determine the modulus of the coating. Damping properties of the samples were also evaluated. This study pays special attention to the dependency of the mechanical performance on the microstructural characteristics of the thermal sprayed ceramic coatings.

Commentary by Dr. Valentin Fuster
2013;():V009T10A067. doi:10.1115/IMECE2013-63843.

Polymers with thermally-reversible Diels-Alder cross-links have been previously shown to heal cracks and regain structural integrity. Complete recovery of fracture toughness has been experimentally observed in neat samples under ideal conditions. In the present work, new healable polymer samples containing glass or carbon reinforcing fibers in [90,0]s cross-ply orientations are fabricated and characterized using dynamic mechanical analysis (DMA). The DMA results are compared with one-dimensional composite and beam analyses. Transverse cracks observed in microscopy images and attributed to residual thermal stresses are considered using a shear lag method. Crack healing is assumed to be occurring as a function of the sample temperature, where the limits of healing are established by other experiments. By considering the composite constituent properties, sample geometries, and the presence of cracks that heal during the test, the DMA measurements are accurately modeled.

Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures and Fluids: Multi-Physics Simulations and Experiments for Solids

2013;():V009T10A068. doi:10.1115/IMECE2013-62519.

In high-rate failure models for geological and rock-like materials, heating due to inelastic deformation is often neglected or accommodated incompletely through the use of an isentropic elastic response. However, for realistic prediction of geomaterials response to high-rate large deformations with significant released energy (such as buried explosive), dissipation caused by the initial mechanical work of the blast wave results in a non-negligible entropy generation that must be accounted for in constitutive modeling. In this study, thermal effects in the vicinity of a buried explosive in partially saturated soil are investigated using the Jones-Wilkins-Lee (JWL++) detonation model of High Explosive (HE) material, along with coupled multiphysics balance equations in an open-source massively parallel computational framework (Uintah) via Material Point Method (MPM) and Implicit, Continuous fluid, Eulerian (ICE) for compressible multi-material formulation of fluid-structure interactions (including highly pressurized explosive gaseous products). The temperature is allowed to evolve according to thermo-plasticity equations (derived from dissipation inequalities and basic conservation/thermodynamics laws) and thereafter, the state of internal variables (porosity, entropy, yield stress, etc) and stress in the partially saturated soil are determined for the obtained temperature. In order to account for material hardening from pore collapse, a yield surface based on Gurson’s upper bound theory evolves with stress, temperature, and internal state variables in plastic phase. Comparisons of soil response to blast loading are provided to quantify the importance of thermal effects.

Furthermore, geomaterials develop anisotropy in their response to deformation caused by prompt high-pressure shock waves. Thermodynamic admissibility implies that the fourth-order tangent stiffness tensor of geomaterials must develop a recoverable deformation-induced anisotropy (RDIA) even if the material is initially isotropic. This effect is significant for materials, like geomaterials, that have strongly pressure-sensitive strength. The degree of RDIA and the required additional terms in the form of deformation-induced anisotropy based on thermodynamics requirements in a high-temperature phenomenon are summarized for the region near the buried explosive source in partially saturated soil.

Commentary by Dr. Valentin Fuster
2013;():V009T10A069. doi:10.1115/IMECE2013-62918.

A magnetic-sensitive rubber (MSR) can change its stiffness and damping characteristics with variant magnetic intensity. Hence, it is possible to use it in dissipating the impact energy adaptively. Although the relationships between elastic modulus, damping ratio and magnetic intensity have been investigated extensively by static tensile, compression or shear experiments as well as vibration tests, few literatures have shown the effectiveness of MSRs on energy dissipating during impact. In this present paper, a group of magnetic-sensitive specimens, composed by ferromagnetic particles with various volume fraction, particle dimensions at millimeter-scale or micrometer-scale, particle arrangement in chain-like or uniform distributions, and rubber matrix with three different types were manufactured. Then, a series of impact experiments aimed to test the capability of MSRs in mitigating shock was conducted by a self-developed drop hammer device with adjustable homogeneous magnetic field. The influences of the above factors on the acceleration responses were investigated. To explain the mechanism, the mathematical model of the impact process was established, and based on it; the acceleration response was obtained by MATLB software. The numerical solutions are validated by comparing with the corresponding test results. It is found that the volume fraction of particles and magnetic intensity has the obvious influences on the dynamic acceleration response, while the arrangement of macro-particle in matrix affects less. Micro-particles can change the characteristics of matrix more significantly than the macro-particles.

Commentary by Dr. Valentin Fuster
2013;():V009T10A070. doi:10.1115/IMECE2013-65048.

Shape memory polymers (SMP’s) are polymers that have the ability to retain a temporary shape, which can revert back to the original shape on exposure to specific triggers such as increase in temperature or exposure to light at specific wavelengths. A new type of shape memory polymer, light activated shape memory polymers (LASMP’s) have been developed in the past few years. In these polymers the temporary shapes are fixed by exposure to light at a specific wavelength. Exposure to light at this wavelength causes the photosensitive molecules, which are grafted on to the polymer chains, to form covalent bonds. These covalent bonds are responsible for the temporary shape and act as crosslinks. On exposure to light at a different wavelength these bonds are cleaved and the material can revert back to its original shape. A constitutive model of LASMP’s which based on the notion of multiple natural configurations has been developed (see Sodhi and Rao [1]). It has been applied to model the circular shear of light activated shape memory polymer with two networks. In this work we use this model to analyze the mechanical behavior of LASMP’s with three different networks undergoing a circular shear deformation cycle. This involves study of the behavior of the LASMP’s when two temporary configurations are formed by exposing the polymer to light at different time during the deformation process. In addition, we show that these materials are able to undergo complex cycles of deformation due to the flexibility with which these temporary configurations can be formed and removed by exposure to light.

Commentary by Dr. Valentin Fuster
2013;():V009T10A071. doi:10.1115/IMECE2013-65356.

Variational integrators have been used to study the transient response of a number of dynamical problems, while displaying superior conservation characteristics. The purpose of this paper is to develop variational integrators for linear piezoelectric problems. A two-field piezoelectric functional is first discretized in space and time and the coupled discrete Euler-Lagrange equations for displacement and electrical potential are then derived. Afterwards, to validate this new formulation, the numerical results for two initial/boundary value problems involving a piezoelectric plate are compared to the corresponding analytical solutions and finite element results obtained from a commercial software package. The excellent correlation of these solutions indicates the capability of variational integrators in modeling transient piezoelectric behavior. Finally, the superior energy conservation behavior of the developed method is demonstrated.

Commentary by Dr. Valentin Fuster
2013;():V009T10A072. doi:10.1115/IMECE2013-65584.

Ductile fracture in thin sheet metals is a common failure mechanism that governs many important industrial applications. A variety of simulation methods, ranging from the atomistic to continuum scales, have been proposed and demonstrated. To assess the capabilities of the existing simulation tools, a group of researchers presented their modeling predictions on the so-called Sandia Fracture Challenge problem at the 2012 ASME IMECE conference. The discrepancies between the simulation and experimental results, and among the experimental results themselves led to consensus that more needs to be done to improve the understanding of this complex phenomenon. Following the participation of the Sandia Fracture challenge, further simulations are performed to study the ductile failure in thin sheet metals with conditions that are commonly used for processing. It is shown that failure pattern and load are significantly influenced by the processing conditions.

Topics: Sheet metal , Failure
Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures and Fluids: Multi-Scale Computations in Fluids, Structures, and Materials

2013;():V009T10A073. doi:10.1115/IMECE2013-64642.

Work presented in this paper describes the formulation for implementation of a concurrent multiple-time-scale integration method with improved numerical dissipation capabilities. This approach generalizes the previous Multiple Grid and Multiple Time-Scale (MGMT) Method [1] implemented for the Newmark family of algorithms. The framework is largely based upon the fundamental principles of Lagrange multipliers used to enforce workless nonholonomic constraints and Domain Decomposition Methods (DDM) to obtain coupled equations of motion for distinct regions of a continuous domain. These methods when combined together systematically yield constraint forces that not only ensure conservation of energy but also enforce continuity of velocities across the interfaces. Multiple grid connections between (non-conforming) sub-domains are handled using Mortar elements whereas coupled multiple-time-scale equations are derived for the Generalized-α Method [2]. We show that MGMT Method can be easily extended to incorporate the Generalized-α family of time integration algorithms, hence allowing selective discretization in space and time along with controlled numerical dissipation for distinct grids. We also show that interface energy across connecting sub-domains is identically zero, further assuring global energy balance and continuity of velocities across connecting sub-domains.

Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures and Fluids: Multiscale Modeling of Fatigue Damage and Failure Mechanics

2013;():V009T10A074. doi:10.1115/IMECE2013-65222.

Thermal oxidation growth and damage evolution are highly coupled as oxidative reactions produce thermal stress and weaker materials leading to crack growth, which in turn accelerates the penetration of oxide layers deeper into the structure. Oxygen diffusion-reaction model can predict the time-dependent oxidation state and evolution of oxide layers in unidirectional composites. With given oxidation state and presumed initial cracks, extend finite element method (XFEM) can be used to calculate the damage evolution due to oxidation-induced stress in the composites. These two models run iteratively to predict the oxidation degradation of polymer composites serving at high temperature.

A probabilistic strength distribution model is formulated in this research to represent the scatter of mechanical properties of composite materials and initiate discrete cracks with Hashin failure criteria. With initiated discrete cracks, damage evolution due to high-temperature thermal oxidation can be calculated. The oxidation growth and damage evolution predicted correlate well with experimental observations. The probabilistic strength distribution model enables crack initiation and damage evolution prediction of use-life and durability of composites structures operating at high temperatures.

Commentary by Dr. Valentin Fuster
2013;():V009T10A075. doi:10.1115/IMECE2013-66084.

The behaviors of model-I fatigue crack propagation behaviors under different strain cycles in single crystal aluminum have been systematically investigated by molecular dynamic and quasicontinuum method with embedded atom potential. Four different crack orientations: (010)[001], (111)[11-2], (110)[001] and (101)[10-1] are investigated by using the edge-crack model. Different fatigue crack growth mechanisms such as cleavage crack propagation, twinning and dislocation emission are observed. Premature crack surface contact during the unloading path is also observed for the (010)[001] crack, which is consistent with the crack closure hypothesis in the classical fatigue theory. The relationship between local deformation and crack growth kinetics are identified by using crack tip increments and crack tip opening displacement (CTOD) profiles at the selected stress cycle. The results show that crack only grows during part of the loading path and no crack growth during the unloading path, which are well in agreement with our previous in-situ SEM observations.

Commentary by Dr. Valentin Fuster
2013;():V009T10A076. doi:10.1115/IMECE2013-66221.

Experimental results have shown that polymer composites that have high fracture toughness tend to have high fatigue wear resistance. The work of fracture found in nacre (mother of pearl) is several orders of magnitude larger than the ceramic (aragonite) it is made of. The organic protein layers in the composite play a significant role in the mechanical response of nacre to stress. In this study, we hope to understand if an energy absorbing interphase similar to that found in nacre could have potential for toughening traditional, glass-particle-reinforced polymer composites. A multi-scale finite element model (FEM) has been developed to study the interaction between the crack and the reinforced particles. In this model, crack nucleation and propagation and the effect of particle/matrix/interphase material properties can all be characterized by the cohesive element and its traction-separation behavior. Loss of load carrying capacity begins when local deformation reaches a certain value, leading to the degradation of the material. Completely degraded elements form a traction-free crack surface. The most important advantage of this methodology for modeling fracture behavior is that macroscopic fracture criteria are not needed. 3-point bending macro-scale FEM serves to calibrate the deformation gradient of the study zone in front of the crack tip. A microscopic unit cell model was used to simulate the crack propagation. Three types of interphase were compared: (1) matrix and particle bonded without interphase, (2) matrix and particle bonded with silane interphase, and (3) matrix and particle bonded with beta-peptide (highly stretchable) interphase. Results show that the stress distribution around the filler and the bulk mechanical properties of the composite can be affected by changes in interfacial properties. Particle-reinforced polymer composites with a more compliant and stretchable interphase (e.g. beta-peptide) will help absorb local strain energy while remaining intact, allowing less damage within the matrix. This type of interphase decreases crack propagation speed and results in an increase of fracture toughness.

Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures and Fluids: Nanocomposites Synthesis and Performance

2013;():V009T10A077. doi:10.1115/IMECE2013-64946.

Thermally sprayed coatings have long been used to develop engineered surfaces for protection from severe degradation due to abrasive/erosive wear. High Velocity Oxy-Fuel (HVOF) thermal sprayed cermet composite coatings based on WC-Co systems offer better wear resistance and greater application flexibility compared with the traditional surface treatment techniques such as hardfacing. Recently, the development of nanostructured surfaces based on HVOF deposition of nano-grain WC reinforced in a variety of alloy matrix based cermet systems have gained research focus thanks to their initial performance results, including high hardness and wear properties without concomitant loss of ductility or fracture toughness in the sprayed coatings. In this research, the novel design and manufacturing of the ‘duplex Co-coated’ nanostructured WC-17Ni(80/20)Cr cermet powder is developed. The spraying of the feedstock is carried out using a diamond jet DJ2600 HVOF spray gun. In this study the mechanical properties of the novel coating are investigated and compared with the industry-standard microstructured WC-10Ni-5Cr coating.

Topics: Wear , Coatings
Commentary by Dr. Valentin Fuster
2013;():V009T10A078. doi:10.1115/IMECE2013-65060.

The objective of this paper is to introduce analytical closed form solutions for the prediction of effective axial and transverse Young’s modulus and Poisson ratios of a matrix-filled nanotube (i.e., a representative element of nanotube reinforced nanocomposites) as well as its mechanical behavior (i.e., displacements, strains and stress distributions) when it is subjected to externally applied uniform axial and radial loads. In this work, both the nanotube and its filler material are considered to be generally cylindrical orthotopic. For the derivation of exact solutions for radial loading case, no plain strain condition is assumed and effects of axial strain is taken into consideration to obtain a more precise set of solutions. Analytical formulae are developed based on the principles of linear elasticity and continuum mechanics and then exact solutions are obtained for displacements, strains and stress distributions within the domain of each individual constituent. To validate and verify the accuracy of the closed form solutions obtained from the analytical approach, a 3-D model of a matrix-filled nanotube is generated and solved for displacements, strains and stresses, numerically, using a finite element method. Excellent agreements were achieved between the results obtained from the analytical and numerical methods.

Commentary by Dr. Valentin Fuster
2013;():V009T10A079. doi:10.1115/IMECE2013-65879.

Room temperature vulcanized (RTV) silicone foams (SFs) have unique thermal and chemical properties due to the presence of inorganic Si-O backbones with organic methyl side groups. However, their low mechanical strength and low tear resistance are major drawbacks for many applications. We have incorporated Nanoclay as reinforcing filler to improve mechanical properties of silicone foams. A three step blending process was used to disperse Nanoclay in silicone elastomers. Initially, Nanoclay in the concentration range of 0.5%–1% by weight were mixed to silicone polymer using a mechanical mixer at 1200 rpm for 10 min followed by a tip sonication at 20% amplitude for 1 hr. Finally, a high speed mechanical mixer was used at 2000 rpm for 2 hours. Two different types of Nanoclays with different sizes were investigated. Both compression and tear properties were found to improve with addition of 0.5 wt% Nanoclay. It was found that the smaller Nanoclay particle size showed the best compressive property while the Nanoclay with larger particle size improved tear strength the greatest.

Commentary by Dr. Valentin Fuster
2013;():V009T10A080. doi:10.1115/IMECE2013-66410.

Effects of sizing and surface modification on flexural properties of carbon fiber reinforced epoxy composites have been investigated. Carbon fiber was desized using three types of treatments, namely heat, acetone, and acetone-acid. In addition, these fibers were coated with three different types of Polyhedral Oligomeric Silsesquioxane (POSS) molecule. Composite panels were fabricated using the vacuum assisted resin transfer molding and samples were tested in flexure. Scanning electron microscopy analysis was performed to investigate the surface morphology and failure mechanisms. It was found that removal of sizing significantly reduced the flexural strength. About 19% and 29% reduction of flexural strength was reported for acetone treatment and heat treatment, respectively. Composites with POSS coated fibers showed improved properties, except for the heat treated fibers. Among POSS molecules investigated, the S10455 was found to be the best for improving the flexural properties of carbon fiber composites.

Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures and Fluids: Nanoengineered, Hierarchical, and Multi-Scale Materials

2013;():V009T10A081. doi:10.1115/IMECE2013-64978.

In this work, the mechanical properties of carbon nanotube reinforced structural adhesive bonds are investigated both theoretically and experimentally. The theoretical investigations employ a novel multiscale modeling technique that integrates governing atomistic constitutive laws in a continuum framework. This technique takes into account the discrete nature of the atomic interactions at the nanometer length scale and the interfacial characteristics of the nanotube and the surrounding polymer matrix. Appropriate formulations are developed to allow for the atomistic-based continuum modelling of nano-reinforced structural adhesive bonds on the basis of a nanoscale representative volume element that accounts for the nonlinear behaviour of its constituents; namely, the reinforcing carbon nanotube, the surrounding adhesive and their interface. This model is used to evaluate the constitutive response of carbon nanotubes with varied chiral indices. The newly developed representative volume element is then used with analytical micromechanical modeling techniques to investigate the homogeneous and dispersion of the reinforcing element into the adhesive considered upon the linear elastic properties.

Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures and Fluids: Nanoscale Mechanics of Polymer Nanocomposites and Nanostructured Materials

2013;():V009T10A082. doi:10.1115/IMECE2013-62439.

Longitudinal elastic mechanical behavior of the armchair and zigzag single-walled carbon nanotubes (SWCNTs) and the SWCNTs reinforced polymer nanocomposites are investigated. Finite element analysis (FEA) models of the SWCNTs and the SWCNTs reinforced polymer nanocomposites are developed utilizing multiscale modeling technique along with molecular structural mechanics (MSM), which provides material properties at molecular scale and establishes relations between the steric potential energy and the classic structural mechanics. Material properties of C-C bond were obtained using multiscale-based modeling method with the consideration of shear deformation. In addition, for the interphase layer interaction between the carbon molecules of SWCNTs and the molecules of polymer matrix, multiscale-based modeling method was utilized to obtain the stiffness of nonlinear spring elements representing the van der Waals interaction. It is observed that the mechanical behavior of the SWCNTs reinforced polymer nanocomposites is dictated by the mechanical behavior of the SWCNTs embedded in the polymer matrix. Furthermore, varying radius and length of the SWCNTs would affect the longitudinal elastic mechanical properties of the SWCNTs reinforced polymer nanocomposites. Specifically, the simulation results had demonstrated that longitudinal elastic mechanical properties of the SWCNTs reinforced polymer nanocomposites would vary due to different loading conditions applied, i.e., discrete and continuous loading conditions.

Commentary by Dr. Valentin Fuster
2013;():V009T10A083. doi:10.1115/IMECE2013-64955.

Nanoindentation tests at the nano-micrometer scales are conducted to investigate the depth and time dependent deformation mechanisms of polydimethylsiloxane (PDMS). Astonishing indentation size effects observed in these experiments are analyzed with an existing theoretical hardness model, and the effects of loading time on the hardness and indentation stiffness of PDMS are studied. The change in the indentation recovery with respect to indentation depth and loading time are analyzed. Furthermore, it is shown that the stiffness of PDMS obtained at the maximum applied force can be efficiently applied to validate the applied theoretical hardness model with the experimental results.

Commentary by Dr. Valentin Fuster
2013;():V009T10A084. doi:10.1115/IMECE2013-65588.

The paper presents the use of nanocompsoites in structural level components to improve their overall performance against unique composite failure modes. A multiscale approach is adopted in order to obtain the overall effective mechanical and thermal properties of the nanocomposite. Those effective properties are used in analyzing the structural components using finite element analysis. The results are demonstrated on a composite T stringer that is widely used as a stiffener for composite panels in aerospace structures. The existence of tows in the manufacturing of such components often results in delamination which reduces the structural integrity. In addition, the bondline interface between the skin and stringer is considered a hot spot where delmaination is susceptible to occur. In this study, we propose the use of nanocompsoites to address this issue and improve their overall performance. Thermal cure and temperature variation is considered in this study and its effect on the failure initiation load will be highlighted. A quantitative comparison from using various CNT weight percentages in the epoxy matrix on the initial damage is provided.

Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures and Fluids: Plenary Session in Mechanics of Solids, Structures, and Fluids

2013;():V009T10A085. doi:10.1115/IMECE2013-62239.

The paper presents an overview of the smoothed finite element methods (S-FEM) which are formulated by combining the existing standard FEM with the strain smoothing techniques used in the meshfree methods. The S-FEM family includes five models: CS-FEM, NS-FEM, ES-FEM, FS-FEM and α-FEM (a combination of NS-FEM and FEM). It was originally formulated for problems of linear elastic solid mechanics and found to have five major properties: (1) S-FEM models are always “softer” than the standard FEM, offering possibilities to overcome the so-called overly-stiff phenomenon encountered in the standard the FEM models; (2) S-FEM models give more freedom and convenience in constructing shape functions for special purposes or enrichments (e.g, various degree of singular field near the crack-tip, highly oscillating fields, etc.); (3) S-FEM models allow the use of distorted elements and general n-sided polygonal elements; (4) NS-FEM offers a simpler tool to estimate the bounds of solutions for many types of problems; (5) the αFEM can offer solutions of very high accuracy. With these properties, the S-FEM has rapidly attracted interests of many. Studies have been published on theoretical aspects of S-FEMs or modified S-FEMs or the related numerical methods. In addition, the applications of the S-FEM have been also extended to many different areas such as analyses of plate and shell structures, analyses of structures using new materials (piezo, composite, FGM), limit and shakedown analyses, geometrical nonlinear and material nonlinear analyses, acoustic analyses, analyses of singular problems (crack, fracture), and analyses of fluid-structure interaction problems.

Commentary by Dr. Valentin Fuster
2013;():V009T10A086. doi:10.1115/IMECE2013-63601.

The vibration behavior of ships is noticeably influenced by the surrounding water, which represents a fluid of high density. In this case, the feedback of the fluid pressure onto the structure cannot be neglected and a strong coupling scheme between the fluid domain and the structural domain is necessary. In this work, fast boundary element methods are used to model the semi-infinite fluid domain with the free water surface. Two approaches are compared: A symmetric mixed formulation is applied where a part of the water surface is discretized. The second approach is a formulation with a special half-space fundamental solution, which allows the exact representation of the Dirichlet boundary condition on the free water surface without its discretization. Furthermore, the influence of the compressibility of the water is investigated by comparing the solutions of the Helmholtz and the Laplace equation. The ship itself is modeled with the finite element method. A binary interface to the commercial finite element package ANSYS is used to import the mass matrix and the stiffness matrix. The coupled problems are formulated using Schur complements. To solve the resulting system of equations, a combination of a direct solver for the finite element matrix and a preconditioned GMRES for the overall Schur complement is chosen. The applicability of the approach is demonstrated using a realistic model problem.

Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures and Fluids: Size Scale Effects in Fracture Process

2013;():V009T10A087. doi:10.1115/IMECE2013-62916.

This paper describes the evaluation of post-fatigue residual strength of scaled laminated composites. The effect of thickness size effects of two scaled specimens on residual strength and stiffness of glass fiber reinforced plastic (GFRP) laminate with neat epoxy matrix and Nanoclay (Nanomer® I.30E) containing epoxy matrix are presented in this paper. The residual strength of a both scaled GFRP specimens with neat epoxy matrix and containing Nanoclay of 3% is determined by conducting tensile test on fatigue cycled after 2,00,000 cycles (R = 0.1). Tensile strength, residual strength and stiffness of both scaled specimens are compared with baseline or standard specimen of 4mm thick. The strength of thicker specimen (4 mm) is less compared to thinner (3mm and 2mm) specimens. The loss in strength due to fatigue loading varies with thickness of specimens, depends on the stiffness of the specimens. This complicates the transfer of mechanical properties from small scale specimen testing to use in the design of large scale structures. The stiffness increases in ply level scaled specimens and decreases in sublaminate level scaled specimens with addition of Nanoclay compared to pure epoxy matrix. The reduction in residual strength is same for different thicknesses of scaled nano-composite specimens. There is a potential in reducing scaling effects in composites with the addition of Nanoclay in matrix.

Commentary by Dr. Valentin Fuster
2013;():V009T10A088. doi:10.1115/IMECE2013-64976.

The multiscale process of material failure from the interatomic bond breaking to the visible crack propagation leads us to explore the validity of linear elastic fracture mechanics (LEFM), particularly for fracture toughness as a constant from nanoscale to macroscale. In the current study, by considering the local virial stress averaged within one lattice, we overcome the barrier of ambiguous crack-tip stress field in molecular dynamics (MD) and perform direct estimation of fracture toughness not through remote stresses. By changing the specimen geometry, i.e., either the crack length or the specimen height (the dimension perpendicular to the crack line), the MD and corresponding finite element method (FEM) solutions show that fracture toughness decreases as the crack length or specimen height decreases. Consequently, fracture toughness cannot be treated as a material constant for nanostructures. The size of the singular stress zone (K-dominance zone) is used to explain the size-dependent behavior of fracture toughness. While the crack length or specimen height decreases, the decreasing K-dominance zone makes the singular part around the crack tip stress not capable of accounting for the full fracture driving force.

Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures and Fluids: Symposium on Applications and Challenges in Full-Field Experimental Methods

2013;():V009T10A089. doi:10.1115/IMECE2013-62332.

In this study, deformation of cylindrical shells under axial compressive load was studied and characterized by a noncontact detection technique, called digital image correlation (DIC). As opposed to commonly used strain gages for measuring structure strains at specific points, the DIC method can render not only 2D but also 3D full-field measurements for strain as well as structure deformation. The accuracy of strain measurement obtained using the DIC method was carefully validated by following ASTM standard E8 for strain measurement using strain gages in tensile tests. The DIC technique provided convenient measurements for characterizing the buckling behaviors of defective cylindrical shell samples. This study has engineering implications for providing 3D strain and deformation analyses to ensure structure reliability and safety.

Topics: Pipes , Buckling
Commentary by Dr. Valentin Fuster
2013;():V009T10A090. doi:10.1115/IMECE2013-63512.

Nowadays, Basalt fiber is obtained increasing attention worldwide as a kind of promising reinforced fiber in composite field, which has the excellent mechanical properties, chemical resistance, comparative low cost, easily processing and abundance resource. In this paper, polyurethane dispersion (PUD) was employed as the surface treatment for the basalt fiber-woven fabric. Basalt woven fabric was washed by acetone solution following by different pick-up ratio PUD treating. Treated BFRP and virgin one were tested by tensile test with AE equipment, comparison and analysis have been carried out in order to discuss the change of mechanical property by changing the PUD treatment’s pick-up ratio and improved mechanical and thermal properties compared with virgin one.

Commentary by Dr. Valentin Fuster
2013;():V009T10A091. doi:10.1115/IMECE2013-64584.

The Virtual Fields Method (VFM) is a technique for computing material properties from full-field data. Recently, a variant of this technique, called Eigenfunction Virtual Fields Method (EVFM) has been proposed and applied to homogeneous linear elastic property evaluation. In this work, we extend this technique to heterogeneous materials by applying it to linear elastic material with exponentially varying elastic modulus. For such materials, there are three constitutive parameters to be evaluated: an elastic modulus, the Poisson’s ratio and a material length scale parameter β that controls spatial variation of the elastic modulus. We consider a plate made of such a material, with a circular hole, subjected to uni-axial tension in this study. The elasticity solution to this problem is synthesized using FEM, and strain fields in the vicinity of the hole are obtained on a rectangular grid. These strain component fields are assembled into an augmented strain matrix, whose eigenfunctions are obtained through Principal Components Analysis (PCA). EVFM is then performed using these eigenfunctions as virtual fields and solution of the resulting system of nonlinear equations yields values for the material parameters that are in excellent agreement with the true values.

Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures and Fluids: Symposium on Fracture and Lifetime of Materials in Honor of A. Chudnovsky 75th Birthday

2013;():V009T10A092. doi:10.1115/IMECE2013-62299.

A glassy material is treated as a mosaic of soft and hard clusters. Plastic shear under high shear stress takes place in soft clusters as a series of elementary local slip and stick processes; stress-strain relations are discussed in terms of these elementary acts and their activation energies. Two special situations are considered: a glass where the initial distribution of soft clusters is created by damaging irradiation or other factors, and disappears in the process of shear, and a glass where interaction of soft and hard clusters maintains a time-independent distribution of activation energies.

Commentary by Dr. Valentin Fuster
2013;():V009T10A093. doi:10.1115/IMECE2013-62501.

New technology has been developed that enables multiwall carbon nanotubes to be discrete, high aspect ratio and well bonded to the composite matrix of choice. Several composite types are examined using tubes of diameter about 12 nm and length about 700nm. Fully discrete, well-bonded tubes are shown to significantly enhance the matrix resistance to fracture and can be placed between fiber plies of composites. The challenges of maintaining the exfoliated state of discrete multiwall carbon nanotubes during composite part assembly from the liquid prepolymer to the cured part are discussed.

Commentary by Dr. Valentin Fuster
2013;():V009T10A094. doi:10.1115/IMECE2013-62536.

Two distinct failure modes of spot welds, interfacial and pull-out failure, are observed in impact of spot-welded structures. Automotive industries prefer pull-out as the predominant failure mode since it makes more use of load-bearing capacity of a joint. For the time being, finite element models for predicting pull-out failure of spot weld have not been well developed. The dependence of failure on the stress state, i.e., a locus in the space of failure strain and stress triaxiality, needs to be known for base metal sheets when modeling spot weld pull-out. Existing failure criteria, with or without physical base, were formulated to provide an effective way to utilize a limited number of tests to reconstruct the failure locus.

This paper is aimed to evaluate influence of failure criterion form for identifying failure parameters on modeling spot weld pull-out. As for material tests, various specimen configurations of metal sheets were designed to obtain stress states around a number of typical stress triaxialities. These test results constructed a set of test data for calibrating failure criterion. The spot-welded joints were also tested two different coupon configurations. The force-displacement curves were obtained, and the deformation fields around the spot weld nugget were achieved with DIC. These test results of joints were utilized to validate the model of spot weld pull-out.

Two prevailing failure criteria, shear-modified Gurson model and Modified Mohr-Coulomb model, were selected to predict the complicated spot weld pull-out failure. Parameters in each of the two failure criteria were identified with material test data. Various simulation results were thereafter obtained based on different failure criteria. The two criteria were evaluated in terms of their predictive capabilities for spot weld pull-out failure.

Topics: Modeling , Failure
Commentary by Dr. Valentin Fuster
2013;():V009T10A095. doi:10.1115/IMECE2013-62607.

Frequency domain analysis offers a very efficient method for the fatigue durability assessment of structures subjected to vibration loading. It also allows engineers to gain valuable insight into system behavior and characteristics that are not easily recognized in the time domain. With some reasonable assumptions, most importantly linearity and steady state behavior, the response of a structure in many engineering applications can be simply evaluated through the “scaling” of the input signal by the Frequency Response Functions (FRFs). In cases where the input is random or stochastic in nature additional assumptions are needed to assess the behavior of the system. Usually such cases assume a stationary and ergodic input signal with a zero mean Gaussian distribution. When making such assumptions the system is still characterized by its FRFs. However, since the input signal is random it can be best described by its Power Spectral Density (PSD). Furthermore, the system response (characterized by the stress tensor) can be evaluated by “scaling” the PSD of the input signal(s) by the magnitude squared of the stress FRFs. The linearity assumption also allows the evaluation of a system response due to multiple inputs through superposition principles.

When using stress based fatigue (to assess the durability of a component or a structure) there are several damage evaluation methodologies that can be used. Traditionally, for time domain analysis the von Mises equivalent stress had been the methodology of choice. More recently critical plane search methods have gained popularity and have shown much better correlation with laboratory experiments and field failures, especially under multi-axial and non-proportional loading. Some of these methods have found their way into frequency domain analysis. This paper highlights the application of critical plane methods for the multi-axial fatigue assessment of engineering structures that are subjected to non-deterministic random vibration. A case study is presented to illustrate the process and shows how the proposed method works.

Commentary by Dr. Valentin Fuster
2013;():V009T10A096. doi:10.1115/IMECE2013-62988.

The James Webb Space Telescope is NASA’s next generation space based telescope. The Optical Telescope Element (OTE) is an infrared system designed to operate at cryogenic temperatures. Its primary mirror consists of 18 segments; each segment is controlled by a series of actuators mounted on the back of each mirror segment. Mission success depends vitally on the actuators, specifically the critical bearing assembly of each actuator’s gear motor. This paper details the methodology employed by NASA and Ball Aerospace to evaluate the lifetime of the bearings and to design life tests which quantitatively offset risk at the system level, in a cost effective manner. The life prediction methodology utilized the Lundberg-Palmgren rule to estimate life, employing a cryogenic service factor developed from consideration of fracture toughness changes expected at cryogenic temperatures. This approach showed the capacity of the bearing system to have significant margin and reliability necessary to endure the requirements of OTE operations, over the life of JWST, under the estimated loads. Baseline test designs were subsequently developed with targets designed to show adequate risk reduction during life testing. Tests were subsequently executed at cryogenic temperatures and targets were shown to be met for the required system level risk tolerance.

Commentary by Dr. Valentin Fuster
2013;():V009T10A097. doi:10.1115/IMECE2013-63039.

Crack layer model provides a comprehensive foundation for modeling of fracture growth, failure analysis, and lifetime prediction. During the past two decades, it has been widely applied for modeling various aspects of brittle fracture in general. This paper illustrates in details the procedure of implementation by an example of slow crack growth in a commercialized high-density polyethylene undergoing creep conditions. Firstly, we determine experimentally the basic parameters employed in constitutive equations of crack layer model such as draw ratio λ, the specific energy of transformation γtr, and drawing stress σdr, etc.. Secondly, we implement crack layer model numerically in lab-developed “Simulator”. The paper provides a paradigm for implementation of crack layer model in slow crack growth, and a blueprint for potential software development that can be used in ranking and the lifetime assessment of a large set of engineering polymers.

Commentary by Dr. Valentin Fuster
2013;():V009T10A098. doi:10.1115/IMECE2013-63062.

Commercial-off-the-shelf column/ball grid array packaging (COTS CGA/BGA) technologies in high-reliability versions are now being considered for use in high-reliability electronic systems. For space applications, these packages are prone to early failure due to the severe thermal cycling in ground testing and during flight, mechanical shock and vibration of launch, as well as other less severe conditions, such as mechanical loading during descent, rough terrain mobility, handling, and ground tests. As the density of these packages increases and the size of solder interconnections decreases, susceptibility to thermal, mechanical loading and cycling fatigue grows even more.

This paper reviews technology as well as thermo-mechanical reliability of field programmable gate array (FPGA) IC packaging developed to meet demands of high processing powers. The FPGAs that generally come in CGA/PBGA packages now have more than thousands of solder balls/columns under the package area. These packages need not only to be correctly joined onto printed circuit board (PCB) for interfacing; they also should show adequate system reliability for meeting thermo-mechanical requirements of the electronics hardware application. Such reliability test data are rare or none for harsher environmental applications, especially for CGAs having more than a thousand of columns.

The paper also presents significant test data gathered under thermal cycling and drop testing for high I/O PBGA/CGA packages assembled onto PCBs. Damage and failures of these assemblies after environmental exposures are presented in detail. Understanding the key design parameters and failure mechanisms under thermal and mechanical conditions is critical to developing an approach that will minimize future failures and will enable low-risk insertion of these advanced electronic packages with high processing power and in-field re-programming capability.

Commentary by Dr. Valentin Fuster
2013;():V009T10A099. doi:10.1115/IMECE2013-63417.

Poly(methylmethacrylate) (PMMA) is one of popular engineering polymers for many engineering applications such as glass substitutes, medical applications, electronic goods, optical fibers, laser disk optical media and so on. PMMA is a lightweight material with excellent optical properties and balanced mechanical properties. However, PMMA is commonly blended with various functional fillers, and rubber particles are one of them to improve the low impact toughness of unfilled PMMA comparing with other engineering polymers such as polycarbonate (PC), acrylonitrile-butadiene-styrene (ABS) copolymer and so on. PMMA is generally used to make exterior of a commercial product, so scratch characteristics of PMMA is very important in terms of the aesthetic point of view.

In this paper, rubber toughened PMMA plates are prepared by injection molding, and static and progressive scratch tests are performed. Samples are prepared by various injection molding conditions, and two orientations (machine direction and transverse direction) of the injection molded plate are considered for scratch tests. Three scratch damage mechanism stages, i.e. mar/ploughing, whitening and cutting stages, are identified by observing the scratch damages and two critical loads to define the variation of scratch damage mechanisms are recorded to evaluate the scratch resistance of rubber toughened PMMA samples. Scratch damage characteristics are examined by various microscopy techniques such as optical microscopy, scanning electron microscopy, transmission electron microscopy, atomic force microscopy, optical profiler and so on. It is clearly observed that scratch damage characteristics of rubber toughened PMMA are changed sensitively for various test conditions due to rubber particles, so it can be known that the mold design should be carefully optimized to improve scratch characteristics of injection molded rubber toughened PMMA product.

Topics: Rubber
Commentary by Dr. Valentin Fuster
2013;():V009T10A100. doi:10.1115/IMECE2013-64485.

There is a strong relationship between fracture mechanics and fatigue. Recently, an energy-based fatigue life prediction method has been studied as a method to quickly, but still accurately determine an SN curve for new materials. In the development of this energy-based fatigue life prediction theory, efforts have concentrated on monitoring stress/strain hysteresis loops only to make life predictions. Thus far, no attempts have been made to link knowledge of fracture mechanics to advances in the energy-based fatigue lifing theory. In this study, notched and unnotched AL6061-T6 flat specimens were fatigued with fatigue monitored by an extensometer. In order to prevent from buckling during hysteresis strain loops, R = −0.5 stress ratio was used. In addition, efforts will concentrate in the low cycle fatigue (LCF) region to support future works on monitoring crack length in fracture mechanics investigation. The goal of this study is to understand how specimens behave in the context of the energy-based fatigue life theory when notches/cracks are present.

Topics: Fatigue life
Commentary by Dr. Valentin Fuster
2013;():V009T10A101. doi:10.1115/IMECE2013-64684.

Fatigue testing is a time and resource-consuming task. Historically, SN testing was conducted at many stress levels on simple representative specimen in order to determine an SN curve, which could then be used to design a component from the same type of material. Recently, an energy-based fatigue life prediction method has been in development. The goal of this method is to quickly determine a material’s fatigue characteristics using simple test procedures. The main theory behind the energy-based fatigue life prediction method is that the strain energy in a monotonic tensile test is equal to the cumulative hysteresis energy of a cyclic test. This theory has always been tested using a single stress level on each specimen. The hysteresis loop information was then used to make fatigue life predictions at other stress levels. Further testing has been done to learn more about the hysteresis energy behavior throughout the lifetime of a specimen, but only for a single stress value. In this study, several stress levels were tested on a single specimen. This new information will help make fatigue life predictions by completely removing the difficult and inconsistent process of determining experimental curve fit coefficients traditionally used in the energy-based fatigue life prediction method.

Commentary by Dr. Valentin Fuster
2013;():V009T10A102. doi:10.1115/IMECE2013-64957.

We consider a stress-assist chemical reaction front propagation in a deformable solid undergoing a localized chemical reaction between solid and gas constituents. The reaction is sustained by the diffusion of the gas constituent through the transformed solid material. We introduce a chemical transformations strain tensor that relates two reference configurations of solid constituents. Then mass, momentum and energy balances are written down for the open system considered and the expression of the entropy production due to the reaction front propagation in a solid with arbitrary constitutive equations is derived. As a result, the expression of the chemical affinity tensor is obtained. Kinetic equation for the chemical reactions front propagation is formulated in a form of the dependence of the front velocity on normal components of the chemical affinity tensor. The locking effect — blocking the reaction by stresses is demonstrated. Finally the kinetic equation for the bulk chemical reaction is derived in a form of the dependence of the reaction rate on the first invariant of the chemical affinity tensor.

Topics: Solids , Stress , Tensors
Commentary by Dr. Valentin Fuster
2013;():V009T10A103. doi:10.1115/IMECE2013-65353.

The invariant integrals are being widely used in the study of defects and fracture mechanics, mostly in elastostatics. However, the properties and the interpretation of these integrals in elastodynamics, especially in the case of time-harmonic excitation, have remained unexplored. Their study has a variety of engineering and geophysical implications, in particular, for the further development of non-destructive evaluation techniques. This contribution is focused on the derivation of the time average J integral for a cylindrical inhomogeneity and M integral for a cylindrical cavity placed in a monochromatic plane elastic wave of arbitrary wavelength. It is shown in the context of antiplane linear elasticity, that the J integral or the material force acting on the inhomogeneity resembles the radiation pressure force exerted on a dielectric cylinder by the normally incident electromagnetic wave. Based on the existing solution of this electrodynamic problem and the corresponding acoustic problem, the J integral is expressed as a function of the nondimensional wave number in the form of the partial wave expansion of the scattering theory. Employing the same classical method as for the J integral, the closed-form solution for the time average M integral for a traction-free cavity is also obtained as a function of the nondimensional wave number. The M integral, i.e., the expansion moment per unit length on an infinitely long circular cavity, is represented in terms of the scattering phase shifts as in the case of the J integral. Rather different expressions for the cavity are also derived for both integrals, which can be used more conveniently for numerical calculations, and these calculations are carried out for J and M integrals in a wide spectrum of frequencies. Asymptotic approximations of both integrals for low and high frequencies are presented. The long wavelength approximation, including the monopole and dipole contributions, has been provided for the J integral in the form of simple analytical expression. The value of M integral in the vanishing frequency limit is also presented. In the opposite short wavelength limit, the corresponding asymptotic values are derived for both integrals. These solutions which are valid for the empty cavity are extended to the case of inviscid fluid-filled cavity. The obtained results can be used in the area of non-destructive evaluation for the flaw characterization by ultrasonic scattering methods. The derived frequency dependence of the J and M integral can be related to the measurable far-field scattering amplitudes. This relationship is relevant to the inverse-scattering approach, which can be applied to the characterization of materials in an attempt to infer geometrical characteristics of flow structures.

Topics: Waves , Cavities
Commentary by Dr. Valentin Fuster
2013;():V009T10A104. doi:10.1115/IMECE2013-65844.

Acoustic Emission (AE) has been studied as a nondestructive testing method for real time damage detection and location studies. The method relies on the propagation of the elastic waves due to the formation of new crack faces. While the method is capable of detecting damage initiation and location with an array of sensors, the variations in geometries and material properties, which change the output response, limit the capabilities of the method in further quantifications in terms of damage size and orientation. The ability to accurately model elastic waves offers significant potential for understanding the AE data; however, the oscillatory nature of wave equation requires very fine meshing and small time step for a stable numerical solution. In this paper, the AE signature of the damage initiation is predetermined using effective numerical models. The numerical model reduces the required degrees of freedom about 60% as compared to conventional finite element formulation and the computational time. Through studying different geometries and materials, it is demonstrated that the crack size and orientation can be identified if the magnitude and the phase of the surface motion are preserved without any modifications due to data acquisition electronics. When the AE sensors are positioned properly, the phase difference of two sensors indicates the crack orientation and direction. The numerical results are validated on monotonic testing of aluminum coupon samples with induced notches at different angles. Understanding the crack orientation provides the directions of the acoustic wave patterns, which improves the source location accuracy with proper wave velocity selection.

Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures and Fluids: Symposium on Mechanics of Adhesion and Friction

2013;():V009T10A105. doi:10.1115/IMECE2013-64166.

Recently, micro- and nano-machine for microelectromechanical systems (MEMS) and the mechanism of bio-adhesive pads and sensors attract great interest. Forces such as the van der Waals force affect the adhesion in nanoscale structures. Even if two bodies does not really contact, adhesion will happen as they approach each other. The adhesion occurs easily in micromachines, so several devices are required to prevent the adhesion. In the present paper, the van der Waals force is introduced into a boundary integral method (BEM) program for analyzing the adhesion in arbitrarily shaped bodies. The van der Waals force is described by a nonlinear function of the distance between two surfaces in close proximity, and the adhesion and repulsion forces vary greatly within the atom equilibrium distance, so the solution for the simultaneous equation in the BEM is hard to converge to an exact solution. In the present paper, we propose a method for converging to a solution, apply it to the adhesion problem between a cylinder and a flat substrate, and compare the solution with the previously published theoretical result. Furthermore, adhesive contact of a semicircular cylinder and a half domain with a wavy surface is analyzed, and the semicircular cylinder is moved to the horizontal direction of the domain. Then, stick-slip phenomenon can be observed and a variation of friction coefficient is discussed. In our analysis, a repeated boundary condition is introduced like a molecular dynamics analysis. So, the program can be used for evaluating the adhesion in a large system.

Commentary by Dr. Valentin Fuster
2013;():V009T10A106. doi:10.1115/IMECE2013-64324.

A numerical solution of elastohydrodynamic lubrication (EHL) contact between two rough surface cylinders is presented. In the theoretical approach the free-volume viscosity model is used to describe the piezo-viscous behavior of the lubricant in a Newtonian Elastohydrodynamic line contact [1,2]. Random rough surfaces with Gaussian and exponential statistics have been generated using a method outlined by Garcia and Stoll [3], where an uncorrelated distribution of surface points using a random number generator is convolved with a Gaussian filter to achieve correlation. This convolution is most efficiently performed using the discrete Fast Fourier Transform (FFT) algorithm, which in MATLAB is based on the FFTW library [4]. The maximum pressure and average film thickness are studied at different values of RMS, skewness, kurtosis, autocorrelation function and correlation length. Numerical examples show that skewness and kurtosis have a great effect on the parameters of EHD lubrication. Surface roughness, indeed, tends to reduce the minimum film thickness and it produces pressure fluctuations inside the conjunction which tend to increase the maximum stress. In this way the dynamic stress increases and tends to reduce the fatigue life of the components.

It can be seen that the pressures developed in the fluid film in the case of rough surfaces fluctuate with the same frequency of the surface roughness. These pressure ripples correspond to the asperity peaks. This indicates that surface roughness causes very high local contact pressures which may lead to local thinning of the film. A significant reduction has been also observed in the minimum film thickness due to surface roughness.

Commentary by Dr. Valentin Fuster
2013;():V009T10A107. doi:10.1115/IMECE2013-64348.

Main motivation for this work is the need for performance evaluation of swelling (and inert) elastomer seals used in petroleum applications. Closed-form (analytical) solutions are derived for sealing pressure distribution along the elastomer seal as a function of material properties of the elastomer, seal geometry and dimensions, seal compression, and differential fluid pressure acting on the seal ends. Seal performance is also modeled and simulated numerically. Good agreement between analytical and numerical results gives confidence that the analytical solution can be used for reliable prediction of sealing behavior of the elastomer. Detailed investigation is then carried out to find out the effect of variation in seal design parameters on seal performance. For both analytical and numerical models, properties of the seal material at various stages of swelling are needed. Therefore, a series of experiments were also designed and conducted to study the effect of swelling on mechanical properties (E, G, K, and ν) of the sealing material.

One major finding is that sealing pressure distribution along the seal is not constant but varies nonlinearly depending on seal parameters and loading conditions, with maximum sealing pressure occurring at the center of the seal length. Longer seals are not necessarily better; after a certain seal length, sealing pressure reaches a steady value for a given set of field conditions. As expected, higher seal compression gives higher sealing pressure. Seal compression can be increased either by tubular expansion or by selecting an elastomer that swells more, or a combination of the two.

Experimental evaluation of swelling-elastomer seal performance can be very costly, and is not even possible in many cases. Numerical simulations, if validated, can be more convenient, but computational effort and cost can be high as simulations have to be run for each set of conditions. Analytical approach presented here not only gives an elegant closed-form solution, but can give reasonably accurate and much faster prediction of elastomer performance under various actual oil and gas field conditions.

Topics: Elastomers
Commentary by Dr. Valentin Fuster
2013;():V009T10A108. doi:10.1115/IMECE2013-65254.

Currently plastic gears are widely used in industry, and not only for lightly loaded applications like household appliances, tools, and toys, but also in the more demanding areas of machinery in automotive applications. However there is a need to investigate important properties such as load capacity, endurance, cost, life, stiffness and wear. Tooth wear is one of the major failure modes in plastic gears just like with steel gears. This paper focuses on the simulation of wear for standard and non-standard gears using an analytical approach. A numerical model for wear prediction of gear pairs is developed. A wear model based on Archard’s equation is employed to predict wear depth. The variation of the contact load generated by the cumulative tooth profile wear is simulated and examined. A MATLAB-based virtual tool is developed to analyze wear behavior of standard and non-standard spur gears depending on various gear parameters. In this paper, this virtual tool is introduced with numerical examples.

Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures and Fluids: Symposium on Mechanics of Integrated Structures and Materials in Advanced Technologies

2013;():V009T10A109. doi:10.1115/IMECE2013-64849.

The in-house developed experimental setup that imitates the wellbore being drilled in presence of surrounding drilling fluid is utilized to investigate the buckling phenomena of drill string. The paper also presents experimental investigations on the effect of changing the friction coefficient on the buckling lock-up situations of drill string. Results reveal that axial transferred loads decrease with the increase of friction coefficient. The results, highlights the significance of changing the drilling fluid rheology, mainly the friction factor, to reduce the friction between the wellbore and the tubing, and thus improve axial force transfer which is mainly responsible for initiation of buckling and limited reach of drilling operation. Drilling fluid with lower friction factor significantly reduces the friction between the tubing and the wellbore. The tube takes the same shape with the change of COF at the same load.

Commentary by Dr. Valentin Fuster

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