ASME Conference Presenter Attendance Policy and Archival Proceedings

2018;():V009T00A001. doi:10.1115/IMECE2018-NS9.

This online compilation of papers from the ASME 2018 International Mechanical Engineering Congress and Exposition (IMECE2018) 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presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.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: Anisotropic Plasticity of Textured and Microstructurally Heterogeneous Materials

2018;():V009T12A001. doi:10.1115/IMECE2018-88197.

We investigate the relationship between the average profile height and the average plastic strain of a grain in a polycrystalline material under plastic tensile strain using Crystal Plasticity Finite Element Method (CPFEM). The simulation consists of using an anisotropic grain embedded in an isotropic sample undergoing tensile plastic deformation. 150 different lattice orientations for the embedded anisotropic grain are used to represent all possible grain orientations. We found that plastic strain in the loading direction is not related to the surface profile height. However, the plastic strains in the direction normal to the surface and the transverse direction are linearly proportional to the average profile heights, irrespective of the grain orientation. The magnitude of the plastic strain in the direction normal to the surface decreases with increasing surface profile height. It is vice versa for plastic strains in the transverse direction. These results establish a possibility of determining a grain’s plastic strains from the profile height.

Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures, and Fluids: Computational Fluid-Structure Interaction

2018;():V009T12A002. doi:10.1115/IMECE2018-87448.

So far, mathematical modelling of Lamb wave propagation under fluid-structure interaction (FSI) was limited to the case of rigid structure. We extend this concept to account for structural dynamics. Thereby, we provide a model that is suitable for the structural health monitoring (SHM) during the operation of the structure. The model we develop is referred to as the “eXtended Fluid-Structure Interaction” (eXFSI) problem, which is a one-directional coupling of typical FSI problem with an ultrasonic wave propagation in fluid-solid and their interface (WpFSI). Here, the strongly coupled problem of acoustic & elastic wave equations is denoted by WpFSI. Next, we explore the approach to the efficient numerical solution of the problem. We use a combination of Finite Element and Finite Difference methods and employ a dual-loop algorithm to balance the computational cost and quality of the numerical solution. To facilitate our solution algorithm, we rely upon the software library package DOpElib.

Commentary by Dr. Valentin Fuster
2018;():V009T12A003. doi:10.1115/IMECE2018-87715.

In this work, we perform a numerical study on the flow induced by the motion of a rigid cantilever beam undergoing finite amplitude oscillations, in a viscous fluid, under a free surface. To this aim, we use a lattice Boltzmann volume of fluid (LB-VOF) integrated method, which includes the tracking of the fluid surface. The adopted approach couples the simplicity of the LB method with the possibility to track the free surface by means of a VOF strategy. Through a parametric analysis, we study the effects related to the depth of submergence, for several values of the oscillation frequency and amplitude. Results are provided in terms of a complex hydrodynamic function, whose real and imaginary parts are the added mass and the viscous damping, respectively, acting on the lamina. Validation of the results is carried out by comparing the solution, for the limit case of lamina submerged in an infinite fluid, with those from available literature studies. We find that the presence of the free surface strongly influences the flow physics around the lamina, especially at low values of the depth of submergence. In facts, when the lamina approaches to the free surface, the fluid waves, generated by the motion of the lamina, interact with the oscillating body itself, giving rise to additional effects, which we quantify in terms of added mass and viscous damping.

Topics: Fluids
Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures, and Fluids: Congress-Wide Symposium on NDE and SHM: Active and Passive Health Monitoring of Structures

2018;():V009T12A004. doi:10.1115/IMECE2018-86067.

Low-temperature cracking is a major form of distress in asphalt concrete pavements located in cold regions. A review of the background and fundamental aspects of the Acoustic Emission (AE) based approach with a brief overview of its application to estimate low-temperature performance of unaged, short-term, and long-term aged binders as well as asphalt concrete materials are presented. A comparison of the cracking temperatures estimated using the traditional rheological-based method and the embrittlement temperatures obtained using the proposed AE-based method is presented and discussed. In addition, embrittlement temperatures of asphalt concrete samples extracted from field cores are also presented and discussed. Results indicate that the AE-based method is faster and more accurate than the traditionally used methods. Moreover, results suggest that AE could be considered as a viable rapid, inexpensive, yet precise characterization approach for pavement materials, which could be effectively used towards enhancing pavement sustainability and resiliency.

Commentary by Dr. Valentin Fuster
2018;():V009T12A005. doi:10.1115/IMECE2018-86221.

This paper investigates the amplitude and sweeping direction dependent behavior of nonlinear ultrasonic resonance spectroscopy for fatigue crack detection. The Contact Acoustic Nonlinearity (CAN) and the nonlinear resonance phenomena are illuminated via a reduced-order bilinear oscillator model. Unlike conventional linear ultrasonic spectroscopy, which would not change its pattern under different amplitudes of excitation or the frequency sweeping direction, the nonlinear resonance spectroscopy, on the other hand, may be noticeably influenced by both the wave amplitude and the loading history. Both up-tuning and down-tuning sweeping active sensing tests with various levels of excitation amplitudes are performed on a fatigued specimen. Short time Fourier transform is adopted to obtain the time-frequency features of the sensing signal. Corresponding to each excitation frequency, a nonlinear resonance index can be established based on the amplitude ratio between the superhamronic, the subharmonic, the mixed-frequency response components and the fundament frequency. The measured nonlinear resonance spectroscopy for a certain amplitude and frequency sweeping direction can be readily used to establish an instantaneous baseline. The spectroscopy of a different amplitude or frequency sweeping direction can be compared with such an instantaneous baseline and a Damage Index (DI) is obtained by measuring the deviation between the two spectra. Experimental investigations using an aluminum plate with rivet hole nucleated fatigue cracks are performed. A series of nonlinear spectroscopies are analyzed for both the pristine case and the damaged case. The spectral features for both cases are obtained to demonstrate the proposed fatigue crack detection methodology which may find its application for structural health monitoring (SHM). The paper finishes with summary, concluding remarks, and suggestions for future work.

Commentary by Dr. Valentin Fuster
2018;():V009T12A006. doi:10.1115/IMECE2018-86222.

In this study, a kind of meta-surface was designed for the improvement of nonlinear ultrasonic guided wave detection by creating bandgaps. It is composed of aluminum alloy cylinders arranged in a periodic pattern bounded on an aluminum plate. By artificially adjusting the height of the cylinders, the meta-surface can open up bandgaps over desired frequency ranges. Guided waves within the bandgap cannot propagate through the meta-surface and will be mechanically filtered out. To perform non-destructive evaluation (NDE) of structural components with fatigue cracks, the guided waves generated by a piezoelectric wafer active sensor (PWAS) propagate into the structure, interact with the crack, acquire nonlinear features, and are picked up by the receiver PWAS. In an ideal case, the waves excited by the transmitter PWAS should only contain signals at the fundamental frequency. However, due to the inherent nonlinearity of the electronic instrument, the generated signals are often mixed with weak superharmonic components. And these inherent higher harmonic signals will adversely affect the identifiability of nonlinear characteristics in the sensing signals. The bandgap mechanism and the wave vector dispersion relationship of the meta-surface are investigated using the modal analysis of a finite element model (FEM) by treating a unit structural cell with the Bloch-Floquet boundary condition. In this way, the meta-surface is carefully designed to obtain bandgaps at the desired frequency ranges. Then, a FEM harmonic analysis of a chain of unit cells is performed to further explore the bandgap efficiency. Finally, a coupled field transient dynamic FEM is constructed to simulate the improved nonlinear ultrasonic guided wave active sensing procedure with the bandgap meta-surface. The proposed method possesses great potential for future SHM and NDE applications.

Topics: Waves , Energy gap , Damage
Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures, and Fluids: Congress-Wide Symposium on NDE and SHM: Nondestructive Characterization of Solids, Structures, and Fluids

2018;():V009T12A007. doi:10.1115/IMECE2018-87158.

The application of composite material in structures can not only lower the component weight but also improve the system performance through its tailorable thermal and mechanical properties. However, because of the harsh environmental conditions that such structures may encounter during operation, the successful applications of such structures cannot be realized without appropriate techniques for their structural integrity evaluation.

In this study, composite cylindrical structures consisting of composite and steel layers are being evaluated with X-ray diffraction technique and various ultrasound techniques. First, X-ray diffraction technique was applied for the quantitative determination of the residual stress in the steel layer. The influence of composite layer on the stress distribution was analyzed and how such residual stress study will improve the performance of the structure was discussed. Then various ultrasound techniques were applied for the detection of various defects, such as the defects at the surface and subsurface of inner steel layer, the different types of defects in the outer composite layer, and the defect, which is the most critical one, at the interface of steel/composite layer. During ultrasound evaluation, the composite material may not only increase the ultrasound attenuation but also change ultrasound traveling direction, and this can make the inspection more challenging. Theoretical calculations were carried out for the optimization of experimental parameters such as ultrasound frequency, incident angle, and focused ultrasound field calculation and so on. The limitations of ultrasound technique and the potential of other non-destructive techniques were also discussed according to experimental results.

Commentary by Dr. Valentin Fuster
2018;():V009T12A008. doi:10.1115/IMECE2018-87681.

Previously published articles on detecting damage in electrically conductive panels mainly concentrate on electrical impedance tomography methods (EIT) which are based on using surface bounded boundary electrodes and taking advantage of an electrically conductive layer on the surface of the panel or of a conductive matrix material. In this study instead, embedded electrodes in glass fiber reinforced epoxy panels are used to locate and quantify the artificial damage inflicted on the panel. The panel was manufactured using vacuum infusion method. It consisted of 10 (S-2) glass fabric plies, where copper electrodes were embedded below the top layer and then vacuum infused with carbon nanotube (CNT) mixed epoxy. During all measurements, a constant electrical current was supplied from two outer electrodes (the source and sink) and changes in voltage from the two inner probes were recorded. In contrast to EIT methods, no complicated algorithm is used to solve the conductivity distribution of the panel but instead, a simple algorithm that fits Gaussian curves to the data obtained using a four-probe measurement technique. Using the fitted curves, we are able to detect location and magnitude of the damages within a confidence bound. This practical method reduces computational cost and also enables the use of embedded electrodes which could provide more durability for the sensors. The experimental data is in very good agreement with the finite element simulations. Comparison of relative voltage change before and after the damages is consistent and sensitive enough to detect damages down to 1/8” diameter hole inside an area of 33 in2. As expected, accuracy is higher for larger diameter holes.

Commentary by Dr. Valentin Fuster
2018;():V009T12A009. doi:10.1115/IMECE2018-88683.

Characterizing the permeation performance of nano-porous material is an initial step towards predicting micro-flows and achieving acceptable designs in sealing and filtration applications. The present study deals with analytical, numerical, and experimental studies of gaseous leaks through soft packing materials.

The paper presents a new analytical model to accurately predict and correlate gaseous leak rates through nano-porous materials. The analytical prediction is done with a model of fluid flow through capillaries of an exponentially varying section. Based on Navier-Stokes equations with different flow regimes, the analytical model is used to predict gaseous flow rates through soft packing materials. In addition, for comparison, computational fluid dynamic modelling using CFX software is used to estimate the flow rate of compression packing ring materials assuming the fluid flow to follow Darcy’s law. Helium gas is used as a reference gas to characterize the porosity parameters. The analytical and CFX numerical leak predictions are compared to leak rates measured experimentally using different gas types (Helium, Nitrogen, Air, and Argon) at different pressures and gland stresses. The packing material is subjected to different compression stress levels in order to change its porosity.

Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures, and Fluids: Deformation and Failure of Multifunctional Materials

2018;():V009T12A010. doi:10.1115/IMECE2018-86063.

A thermodynamically consistent constitutive model of metallic glass is presented by extending the infinitesimal deformation model of Huang et al. [Huang, R., Suo, Z., Prevost, J. H., and Nix,W. D., 2002.Inhomogeneous deformation in metallic glasses,J. Mech. Phys. Solids, 40, 1011–1027] to finite deformation. The underlying theory behind the model is the free volume theory with free volume concentration as the order parameter affected through the processes of diffusion, annihilation and creation. The main assumptions of the model include multiplicative decomposition of deformation gradient and additive decomposition of free energy. The former comprises of elastic, inelastic dilatational component associated with excess free volume concentration and isochoric plastic part while the latter consists of contributions from elastic deformation and free volume concentration. The plastic part evolves according to Mises-theory and the local free volume concentration. Homogeneous simple shear is the model problem solved using the present model and compared with the infinitesimal deformation theory to examine the effect of large deformation on stresses in metallic glasses.

Commentary by Dr. Valentin Fuster
2018;():V009T12A011. doi:10.1115/IMECE2018-86122.

In armored platforms industry, the dominant material solution for ballistic transparency protection applications is relatively low-cost polycarbonate matrix glass. This research work aims to investigate the effects of geometrical designs of the amalgamated layers, engineering characteristics of the materials, and the interaction of both on the ballistic resistance of the transparent armor. The resulted models are used to analyze the strength feasibility of the material in the cost base. Ballistic measurements over a wide range of impact velocities including those well above the ballistic limits are deployed to the model. Under simple loading conditions, the polycarbonate matrix glass or ceramic can be regarded as elastic-brittle materials, however, when considering ballistic impacts the post-yield response of the ceramic becomes significant. A post-yield response model of ceramic materials is used for simulating the characteristics. The model incorporates the effect of damage on residual material strength and the resulting bulking during the compressive failure of the ceramic. A combination of relevant factors including the ability to dissipate ballistic energy and manufacturing processes was considered for the proper evaluation and selection of the armor. The model has been implemented into computer software to predict unsuccessful solutions and optimize the amalgamation with capabilities of defeating a wider range of ballistic impacts. The results will show more physical insight of the behavior and performance of the complex armor systems and provide guidelines/principles for the design and selection of the constituent materials.

Commentary by Dr. Valentin Fuster
2018;():V009T12A012. doi:10.1115/IMECE2018-88512.

Sudden concrete failure is due to inelastic deformations of concrete subjected to tension. However, synthesizing nanomaterials reinforcements has significant impact on cement-based composites failure mechanism. Nanomaterials morphology bridges cement crystals as homogeneous and ductile matrix.

In this experiment, cement matrix with water to cement ratio of 0.5 reinforced by 0.2–0.6 wt% of functionalized (COOH group) multi-walled and single-walled carbon nanotubes were used. After sonication of carbon nanotubes in water solution for an hour, the cementitious nanocomposites were casted in cylindrical molds (25 mm diameter and 50 mm height). Failure mechanism of cementitious nanocomposite showed considerable ductility throughout splitting tensile test compared to cement mortar. Additionally, the failure pattern after developing the initial crack provided additional time before ultimate failure occurred in cement-based nanocomposites. The evolution of crack propagation was assessed until ultimate specimen failure during splitting-tensile test on cementitious nanocomposite surface. The deformation of cross section from circle to oval shape augmented tensile strength by 50% in cementitious nanocomposite compared to conventional cement mortar.

Commentary by Dr. Valentin Fuster

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

2018;():V009T12A013. doi:10.1115/IMECE2018-87110.

This study compares the deformation characteristics of steel and carbon fiber composite (CFC) front bumper crush can (FBCC) assemblies when subjected to a full-overlap frontal impact into a rigid wall. Both the steel and composite bumper tests were conducted using a sled-on-sled testing method. Several high-speed cameras (HSCs) and accelerometers were used to gather kinematics data. The applied forces were measured using a load cell wall. For each test, the collective set of data was filtered, sorted, and analyzed to compare the performance of the steel and CFC bumpers.

Similarities in Acceleration-Time plots suggested resemblance in the deformation patterns for both types of bumper systems. The difference observed in the velocity and displacement time-histories was because of the brittle nature of the composite material. The velocity-time history of the CFC FBCC had two distinct patterns, events suggesting adhesive bond failure between the bumper beam and the crush cans, which was validated through video tracking. Post-impact photographs showed a clear difference between the material behavior of composite and steel bumpers when subjected to high-velocity impact. The steel bumper beam was bent uniformly with intact, equally crushed crush cans. The composite beam was cracked in the middle and was detached from the crush cans.

Commentary by Dr. Valentin Fuster
2018;():V009T12A014. doi:10.1115/IMECE2018-87855.

Many engineering structures, in applications such as automobiles, bridges, etc. are assembled by joining the different parts together. Therefore, joints in the mechanical applications play a critical role in durability, flexibility of the mechanical assemblies. Recent advances in adhesive technology have made adhesive joining one of the plausible options in many engineering applications that demand high impact resistance such as ground vehicle armor or civilian vehicles. However, because most of the polymer-based adhesives have non-linear mechanical behavior and loading rate sensitivity caused by their viscoelastic properties, characterization of the adhesives under different loading and environmental conditions become vital in the design of durable and reliable joints in any structure. This study investigated the mode I (bending) response of the adhesive joints to shock-wave loading generated in a large-scale shock tube. The critical failure pressure (P5) of adhesive joints was determined experimentally. Determining the material properties of the adhesive were estimated by the FEM parametric study, and energy absorption capacity of the adhesive joints under different strain rate loadings were investigated.

Commentary by Dr. Valentin Fuster
2018;():V009T12A015. doi:10.1115/IMECE2018-88294.

The microstructural design has an essential effect on the fracture response of brittle materials. We present a stochastic bulk damage formulation to model dynamic brittle fracture. This model is compared with a similar interfacial model for homogeneous and heterogeneous materials. The damage models are rate-dependent, and the corresponding damage evolution includes delay effects. The delay effect provides mesh objectivity with much less computational efforts. A stochastic field is defined for material cohesion and fracture strength to involve microstructure effects in the proposed formulations. The statistical fields are constructed through the Karhunen-Loeve (KL) method. An advanced asynchronous Spacetime Discontinuous Galerkin (aSDG) method is used to discretize the final system of coupled equations. Application of the presented formulation is shown through dynamic fracture simulation of rock under a uniaxial compressive load. The final results show that a stochastic bulk damage model produces more realistic results in comparison with a homogenizes model.

Commentary by Dr. Valentin Fuster
2018;():V009T12A016. doi:10.1115/IMECE2018-88461.

The failure of engines on jet aircrafts during the past few years has prompted the National Transportation Safety Board (NTSB) to issue an “urgent” recommendation to increase inspections of the engines on U.S. aircraft. Such uncontained engine failures are particularly dangerous, because flying engine parts could puncture fuel or hydraulic lines, damage flight surfaces or even penetrate the fuselage and injure passengers. At issue is older engines found on small number of jets, and the safety and economic impact damage and fracture risk can have on aircraft engines. For example, high-pressure turbine blades are commonly removed from commercial aircraft engines that had been commercially flown by airlines. These engines were brought to the maintenance shop for refurbishment or overhaul. The blades were removed and inspected for damage. The damage was cataloged into three modes of failure, which are thermal-mechanical fatigue (TMF), Oxidation/Erosion (O/E), and Other (O). These show the complexity of damage in turbine engines and the different mechanisms associated with cause of damage. Hence, life prediction of turbine engine is crucial part of the management and sustainment plan to aircraft jet engine. Fretting is often the root cause of nucleation of cracks at attachment of structural components at or in the vicinity of the contact surfaces. Previous effort presented a model to predict fretting fatigue in turbine engine, which is one of the primary phenomena that leads to damage or failure of blade-disk attachments. The influence of thermal effect and temperature fluctuation during engine operation on fretting fatigue damage were investigated. Leveraging these existing capabilities, the present effort focuses on modeling another important damage mechanism in turbine engine blades, which is erosion at high temperatures. Thus a reaction-diffusion model is implemented in addition to the thermo-mechanical one. The model provides a mean to investigate erosion initiation and propagation in turbine engine blades.

Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures, and Fluids: High-Performance Nanostructural Materials and Nanocomposites

2018;():V009T12A017. doi:10.1115/IMECE2018-87566.

An analytical modeling was performed to investigate the effect of Nano filler on the mechanical performance of carbon fiber reinforced composite joints using the characteristic curve method. The joints were prepared from carbon fiber reinforced laminated plates with and without graphene nanoplatelet (GNP) and the characteristic dimensions used to determine the characteristic curve were evaluated from stress functions without experimental tests. The load-bearing capacity of the joints were carried out using different coefficient of friction and Yamada-Sun failure criterion along the characteristic curve. The evaluated results showed that the infusion of graphene nanoplatelet into the epoxy matrix of fiber reinforced composite plate increases the failure load of the composite joints.

Commentary by Dr. Valentin Fuster
2018;():V009T12A018. doi:10.1115/IMECE2018-88172.

Stretching properties of single-walled carbon nanotubes (CNTs) of large diameters are studied in atomistic simulations. The simulations are performed based on the AIREBO empirical interatomic potential for three types of CNTs: Nanotubes with circular cross section, permanently collapsed nanotubes with “dog-bone”-shaped cross sections, and collapsed nanotubes with intra-tube covalent cross-links. In the last case, the cross-links between parallel quasi-planar parts of the nanotube wall are assumed to be formed by interstitial carbon atoms. The calculated equilibrium shape of collapsed nanotubes and the threshold diameter for permanently collapsed CNTs are found to agree with existing literature data. Elastic modulus, maximum stress, and strain at failure are calculated for zigzag CNTs with the equivalent diameter up to 6.27 nm in the temperature range from 5 K to 500 K. The simulations show that these mechanical properties only moderately depend on the diameter of circular CNTs. For collapsed CNTs with and without cross-links, the mechanical properties are practically independent of the CNT diameter for nanotubes with diameters larger than 4.7 nm. The elastic modulus and maximum stress of collapsed nanotubes are found to be smaller than those for the equivalent circular CNTs. The intra-tube cross-linking increases the elastic modulus and strength of collapsed CNTs in up to 50% compared to corresponding collapsed CNTs without cross-links, but reduces the breaking strain. Thermal softening of CNTs with increasing temperature in the range from 100 K to 500 K induces a decrease in the elastic modulus and maximum stress in about 12–33%.

Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures, and Fluids: Mechanical Characterization in Extreme Environments

2018;():V009T12A019. doi:10.1115/IMECE2018-86365.

The use of glass-fiber reinforced plastic (GRP) can reduce the weight of tanks significantly. By replacing steel with GRP in tanks for gases (propane, etc.) a weight reduction of up to 50 % was reached. In this project not only the material should be optimized, but also the design. Previous tanks consist of a double-walled structure with an insulation layer between the two shells (e.g. vacuum). Goal of this project is to realize a single-walled construction of GRP with an insulation layer on the outside.

To determine the temperature dependent material values, two different experiments are performed: In the first experiment, temperature dependent material properties of liquid nitrogen found in literature research are validated in a simple setup. The level of liquid nitrogen in a small jar is measured over the experiment time. Numerical simulation shows the change of nitrogen level with sufficient precision. In the second experiment, a liquid nitrogen is applied on one side of a GRP plate. Temperature is measured with thermocouples on top and bottom of the GRP plate, as well as in the middle of the plate. By use of numerical simulation, temperature dependent thermal conductivity is determined.

In the third experiment, a test stand is designed to examine different insulation materials. In this test stand, the insulation material can easily be changed. A numerical simulation, in which the determined material data is used, is performed as well for this test stand.

The experiments show, that GRP can be used in cryogenic environments. Multiphase simulations are a suitable tool to describe the energy absorption of thermal energy due to thermal phase change. Results on different insulation materials will follow.

Commentary by Dr. Valentin Fuster
2018;():V009T12A020. doi:10.1115/IMECE2018-88181.

This paper investigates the thermal and radiation performance of 3D-printed ULTEM materials following ASTM standard D638. ULTEM is a thermoplastic in the polyetherimide (PEI) family that is regularly used as a high-grade material for 3D printing. This material has similar properties to polyether ether ketone (PEEK), which is another thermoplastic that has strong mechanical properties at elevated temperature conditions. While PEEK has stronger mechanical properties, ULTEM is significantly more cost efficient to acquire and process via 3D printing. Also, most 3D printers are unable to utilize PEEK because of the significantly higher temperature requirements this material imposes on a 3D printer.

This work is motivated by the need to rapidly deploy robotic inspection systems within a nuclear canister environment, which exposes the material to temperatures up to 170°C (340°F), and radiation levels of 270 Gy/hr (27 krad/hr), which are significantly beyond that of conventional 3D-printed parts. The design analysis was performed via an experiment consisting of three treatment groups of dogbone ULTEM test pieces. After tensile testing all of the pieces, the material properties were compared to those of the control group.

These results allow manufacturers to select a more cost-effective material to build parts to operate in such a harsh high-temperature, high-radiation environment, which could include applications in both space systems and nuclear inspection robotics. Specifically, the results were used to guide the development of a robust robotic inspection system for the Nuclear Energy University Program (NEUP) by replacing complex parts with easily-fabricated 3D-printed ULTEM pieces.

Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures, and Fluids: Mechanical Metamaterials

2018;():V009T12A021. doi:10.1115/IMECE2018-87050.

Functional metamaterials are gradually becoming the frontier of scientific research and industrial applications. Among them, reconfigurable mechanical metamaterial with inbuilt motion capability could result in unusual physical properties such as shape tunability and programmable density and stiffness. Inspired by the transformable cuboid structure that was first investigated by Ron Resch, we proposed a tilted cuboid structure that can fold into a 3D configuration. By designing the individual building units, face angles and tessellation pattern, we are able to construct a series of reconfigurable structures with various shape, twist and permeability feature. Based on our approach, a configuration method to build multi-layer metamaterial is proposed, and it can be generalized to other tilted structures with different building units. The volumetric strains of different models are analyzed, and the result shows the metamaterial has a massive deformation ability as the maximum volume can be four times of the packaged volume. The tilted cuboid structure is highly flexible with variable stiffness and permeability, and can be used to develop metamaterials, large deformation devices and kinetic architectures.

Commentary by Dr. Valentin Fuster

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

2018;():V009T12A022. doi:10.1115/IMECE2018-86231.

A non-linear regression model using SAS/STAT (JMP® software; Proc regression module) is developed for estimating the elastic stiffness of finite composite domains considering the combined effects of volume fractions, shapes, orientations, inclusion locations, and number of multiple inclusions. These estimates are compared to numerical solutions that utilized another developed homogenization methodology by the authors (dubbed the generalized stiffness formulation, GSF) to numerically determine the elastic stiffness tensor of a composite domain having multiple inclusions with various combinations of geometric attributes. For each inclusion, these considered variables represent the inclusions’ combined attributes of volume fraction, aspect ratio, orientation, number of inclusions, and their locations. The GSF methodology’s solutions were compared against literature-reported solutions of simple cases according to such well-known techniques as Mori-Tanaka and generalized self-consistent type methods. In these test cases, the effect of only one variable was considered at a time: volume fraction, aspect ratio, or orientation (omitting the number and locations of inclusions). For experimental corroboration of the numerical solutions, testing (uniaxial compression) was performed on test cases of 3D printed test cubes.

The regression equation returns estimates of the composite’s ratio of normalized longitudinal modulus (E11) to that of the matrix modulus (Em) or E11/Em when considering any combination of all of the aforementioned inclusions’ variables. All parameters were statistically analyzed with the parameters retained are only those deemed statistically significant (p-values less than 0.05). Values returned by the regression stiffness formulation solutions were compared against values returned by the GSF formulation numerical and against the experimentally found stiffness values. Results show good agreement between the regression model estimates as compared with both numerical and experimental results.

Commentary by Dr. Valentin Fuster
2018;():V009T12A023. doi:10.1115/IMECE2018-86916.

Square tubes are primarily used in automotive structures to absorb energy in the event of an accident. The energy absorption capacity of these structural members depends on several parameters such as tube material, wall thickness, axial length, deformation modes, locking strain, crushing stress, etc. In this paper, the work presented is a continuation of research conducted on exploring the effects of the introduction of cellular core in tubular structures under axial compressive loading. Here, the crushing response of composite cellular core tube was numerically studied using ABAQUS/Explicit module. The energy absorbing characteristics such as deformation or collapsing modes, crushing/ reactive force, crushing stroke, and energy curves were discussed. The composite cellular core tube shows promise for improving the crashworthiness of automobiles.

Commentary by Dr. Valentin Fuster
2018;():V009T12A024. doi:10.1115/IMECE2018-86921.

Thin walled members such as square tubes are commonly used in vehicle’s frontal chassis to provide protection and damage attenuation to the passenger cabin in the case of impact loading. These structural members undergo progressive deformation under axial loading. The type of deformation mode is critical as it defines the overall configuration of force-displacement curve. There are different types of deformation modes for square tube under axial loading. Likewise, cellular structure exhibit distinct deformation modes under in-plane loading. The work presented here investigates the effects of partial or discrete bonding of cellular core structure on deformation modes of square tubes under axial loading. The results show that discrete bonding of cellular core with the tube has significant effect on progressive deformation of tubes and therefore, presents an opportunity to re-configure force-displacement curve for improved protection of automobile structures under impact loading.

Commentary by Dr. Valentin Fuster
2018;():V009T12A025. doi:10.1115/IMECE2018-87231.

Plant petioles and stems are hierarchical structures comprising cellular tissues in one or more intermediate hierarchies displaying quasi random to heterogeneous cellularity that governs the overall structural properties. Exact replication of natural cellular tissue leads to the investigation of mechanical properties at the microstructural level. However, the micrographs often display artifacts due to experimental procedure and prevent representative spatial modeling of the tissues. Existing methods such as local thresholding or global thresholding (Otsu’s method) fail to effectively remove the artifacts. Hence, an efficient algorithm is required that can effectively help to reconstruct the geometric models of tissue microstructures by removing the noise. In this work, perception-based thresholding that conceptually works like human brain in differentiating noise from the actual ones based on color is introduced to remove discrete (within a cell) or adjacent (to the cell boundaries) noise. A variety of image dataset of non-woody plant tissues were tested with the algorithm, and its effectiveness in eliminating noise was quantitatively compared with existing noise removal techniques by Bivariate Similarity Index. The bivariate metrics indicate an enhanced performance of the perception-based thresholding over other considered algorithms.

Commentary by Dr. Valentin Fuster
2018;():V009T12A026. doi:10.1115/IMECE2018-87631.

Non-pneumatic tires (NPTs) have drawn attention mainly due to low contact pressure and low rolling resistance due to use of hyper-elastic materials in their construction. In this paper, an attempt to innovate the conventional design of NPT with hexagonal honeycomb cellular structure is made by creating the boundary planar geometries of the tire, skew to each other at a certain angle. Adding to the functionality as a tire, this modified structure increases the performance of automobile components by rejection of heat through convection (forced) at the expense of engine power. The primary investigation includes study of the effects of variation in degree of skewness with the strength and flow of air through the tire. The flow parameters are computed for rotational case and the heat transfer is computed for flow over a brake disk. The secondary investigation consists of finding an optimum range of the degree of skewness. The validation for strength is computed through Finite Element Analysis. The fluid flow is computed through Computational Fluid Dynamics approach in ANSYS Fluent. This modified structure improves the aerodynamic condition near the brake rotor that increases the rate of heat rejection by forced convection from the brake rotor surface.

Topics: Tires
Commentary by Dr. Valentin Fuster
2018;():V009T12A027. doi:10.1115/IMECE2018-87859.

Auxetic structures exhibiting non-linear deformation are a prevalent research topic in the material sciences due to their negative Poisson’s ratio. The auxetic behavior is most efficiently accomplished through buckling or hinging of 3d printed structures created with soft or flexible materials. These structures have been hypothesized to have some unique characteristics and may provide advantages over conventional engineering materials in certain applications. The objective of present study is to gain a better understanding of behavior of auxetic structures subjected to tensile, compressive and impact loads and assess geometric parameters affecting these structures in applications such as impact shielding or biomedicine. Analytical and experimental methods were employed to investigate two different types of auxetic structures which were 3d-printed with TPU (thermoplastic polyurethane). The first was based on symmetric re-entrant angles cells patterned to form sheet-like structure. Rotation of members in opposite directions in a cell induces negative Poisson’s ratio when the structure is subjected to tensile loading. The second structure was based on rectangular lattice of circular holes. This structure exhibited auxeticity due to formation of pattern of alternating mutually orthogonal ellipses when subjected to compressive and impact loads.

Parameters of interest in this study included hardness of the plastic used in printing the structures, the fill pattern of 3d-printed solid parts, porosity of cylinders in the lattice structure, angles and thickness of members in the re-entrant structure. Preliminary results indicated that per unit weight of material, the re-entrant structure requires less tensile load to strain than a solid structure. This is advantageous in applications where expansion in lateral direction is required. The lattice of circular holes structure exhibited similar trend in impact and compressive loading. The results indicate that geometric parameters influence auxeticity of the structure a great deal. When the porosity of the lattice is too small, positive Poisson’s ratio is observed. The length to height ratio of the re-entrant cell has similar effect on the structure’s Poisson’s ratio. The main advantage gained by employing such structures is their overall ability to resist buckling and withstand impact load without cracking. This study will help to develop 3D-printing techniques in manufacturing better performing structures under similar conditions.

Commentary by Dr. Valentin Fuster

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

2018;():V009T12A028. doi:10.1115/IMECE2018-88109.

In this study, a micro-mechanical model for constitutive behavior of elastomers subjected to thermo-oxidative aging is proposed. The model is based on the network decomposition concept and lies within the framework of continuum mechanics. It is assumed that the aging process leads to the formation of a new network with tighter chains. Accordingly, the strain energy of the system is constituted of two independent sources, the energy of the original soft network and the one of the reformed network. These strain energies were computed by integration of entropic energy of polymer chains in each direction of a micro-sphere. The model demonstrates good agreement with different experimental data on relaxation and intermittent tests.

Topics: Elastomers
Commentary by Dr. Valentin Fuster
2018;():V009T12A029. doi:10.1115/IMECE2018-88228.

The inverse Langevin function has a crucial role in different research fields, such as polymer physics, para- or superpara-magnetism materials, molecular dynamics simulations, turbulence modeling, and solar energy conversion. The inverse Langevin function cannot be explicitly derived and thus, its inverse function is usually approximated using rational functions. Here, a generalized approach is proposed that can provide multiple approximation functions with a different degree of complexity/accuracy for the inverse Langevin function. While some special cases of our approach have already been proposed as approximation function, a generic approach to provide a family of solutions to a wide range of accuracy/complexity trade-off problems has not been available so far. By coupling a recurrent procedure with current estimation functions, a hybrid function with adjustable accuracy and complexity is developed. Four different estimation families based four estimation functions are presented here and their relative error is calculated with respect to the exact inverse Langevin function. The level of error for these simple and easy-to-use formulas can be reduced as low as 0.1%.

Topics: Approximation
Commentary by Dr. Valentin Fuster
2018;():V009T12A030. doi:10.1115/IMECE2018-88234.

The mechanical behavior of polymers has long been described by the non-Gaussian statistical model. Non-Gaussian models are generally based on the Kuhn-Grün (KG) distribution function, which itself is derived from the first order approximation of the complex Rayleigh’s exact Fourier integral distribution. The KG function has gained such a broad acceptance in the field of polymer physics that the non-Gaussian theory is often used to describe chains with various flexibility ratios. However, KG function is shown to be only relevant for long chains, with more than 40 segments. Here, we propose a new accurate approximation of the entropic force resulted from Rayleigh distribution function of non-Gaussian chains. The approximation provides an improved version of inverse Langevin function which has a limited error value with respect to the exact entropic force. The proposed function provides a significantly more accurate estimation of the distribution function than KG functions for small and medium-sized chains with less than 40 segments.

Topics: Elasticity , Rubber , Chain
Commentary by Dr. Valentin Fuster
2018;():V009T12A031. doi:10.1115/IMECE2018-88252.

While single network hydrogels show limited extensibility and low strength, double-network hydrogels benefit from significantly high stretchability and toughness due to their reinforcing mechanism of combining two soft and rigid networks. Here, a micro-mechanical model is developed to characterize the constitutive behavior of DN hydrogels in quasi-static large deformation. In particular, we focused on describing the permanent damage in DN gels under large deformations. Irreversible chain detachment and decomposition of the first network are explored as the underlying reasons for the nonlinear inelastic phenomenon. The proposed model enables us to describe the damage and the way it influences the micro-structure of the gel. The model is validated with uni-axial loading and unloading experiments of DN gels. The proposed model contains a few numbers of material constants and shows a good agreement with cyclic uni-axial test data.

Topics: Stress , Modeling , Hydrogels
Commentary by Dr. Valentin Fuster
2018;():V009T12A032. doi:10.1115/IMECE2018-88265.

Multi-level helical twisted structures represent an example of how natural design achieved an optimized approach for creating a tough and strong fiber from often weak and soft microscale yarns through a hierarchical architecture. In this work, a constitutive model is presented to describe the load transfer within a double twisted helical structures in large deformation regime. The model aims to establish the torsion-tensile properties of fibers as an assembly of twisted yarns and filaments. The model associates the fiber response to the mechanics and the geometry of yarns in the deformed state. In this work, we mainly focus on elastic response of the material and thus inelastic damages were not considered. We modeled the inter-yarn forces that can cause friction. By considering the deformation induced changes in the geometry of constituents, the model describes the influence of the fiber composition parameters such as helical angel of the filaments, prestretch, pretwist of the yarns and the inter-yarn frictions, on the mechanical response of fibers. The model provides a detailed outlook into load transfer within fibers which helps us understand how to design fibers with certain performance.

Topics: Yarns , Torsion , Modeling
Commentary by Dr. Valentin Fuster

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

2018;():V009T12A033. doi:10.1115/IMECE2018-86592.

A physical prototype of a human esophagus has been developed for reproducing the human swallowing process with the aim of studying various disorders that impair its function as well as for the development of new foods and technologies for their treatment. Several studies related to the peristalsis phenomena have been conducted in recent years by studying the effect of different parameters defining the peristaltic wave. Mathematical models have been developed to investigate the impact of an integral and a non-integral number of waves during the swallowing of food stuff such as jelly, tomato puree, among others. Swallowing through the esophagus has not only been studied numerically but also reported by using a pneumatic soft actuators. In the present work, the development of a soft actuator mechanism to reproduce the peristaltic wave as the one reported by F.J. Chen et. al. 2014 is described. Such a mechanism consists of a rubber structure that contains an array of chambers actuated by pressurized air to generate the peristaltic wave. The final chamber shape was determined after an iterative process, which involves the elastomer properties, different chamber shapes, finite element analysis and image processing. The characterization of the developed peristaltic mechanism was made by correlating a theoretical study of swallowing peristaltic model and the waveform obtained from the X-ray radiography analysis as the mechanism is actuated. As result, the soft actuator mechanism can reproduce a peristaltic waveform with a correlation coefficient near to 0.9 with respect to the mathematical model reported in literature. In addition, the manufacturing process based on additive manufacturing technologies is also presented.

Topics: Actuators , Shapes
Commentary by Dr. Valentin Fuster
2018;():V009T12A034. doi:10.1115/IMECE2018-87104.

We introduce a sensor concept for an integrated measurement of the curvature angle of soft bending actuators using inertial measurement units (IMUs). In particular, IMUs are placed at both ends of the soft bending actuator, and the integrated magnetic sensors are used for small and the integrated acceleration sensors for medium and large inclination angles of the soft actuator’s bending plane. The experimental results show absolute measurement errors of up to 20° for small and less than 5° for medium and large inclination angles. Furthermore, we investigate experimentally whether the assumption of a constant curvature in our sensor concept is still fulfilled when the soft bending actuator is loaded by an external force at its free end. The results indicate that this is the case for loading masses of up to 30 g at large inclination angles.

Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures, and Fluids: Mechanics of Thin-Film and Multi-Layer Structures

2018;():V009T12A035. doi:10.1115/IMECE2018-86074.

Two approaches for increasing the load capacity of plastic gears in general are proposed and investigated: modifying the conventional involute profile of the gear tooth surfaces by applying a parabolic-crowned profile, and introducing a composite fabric, which blankets the surface of the teeth. The investigation is carried out using the finite element method (IGD/ANSYS). A five-tooth model is applied for the gears, and nylon and carbon/nylon are adopted for the materials. The evolution of maximum contact and bending stresses is evaluated over two cycles of meshing for both the pure plastic (nylon) gears and the gears with the composite surface blanket (carbon/nylon) to investigate the process of transfer of load between consecutive pairs of teeth and detect possible edge contacts. The results indicate that selecting the proper parabolic-crowned profile helps to alleviate the contact stress, and more specifically, to reduce the peaks of contact stresses due to edge contacts at the tip of the teeth. The results also indicate that there are an optimum parabolic-crowned profile and an optimum thickness of the composite blanket, which render the lowest maximum level of contact stresses over the cycle of meshing and bending stresses at the fillet. However, this preliminary research work suggests that, for the case considered, the novel idea of composite blanket is inconclusive — though the blanket may protect the plastic core, it itself becomes vulnerable to failure. The idea is being explored more, and the results will be disseminated in a future work.

Commentary by Dr. Valentin Fuster
2018;():V009T12A036. doi:10.1115/IMECE2018-86308.

The aim of this study is mainly about preventing crack initiation and propagation in rolling contact under moderate and extreme loading through coating technology using finite element simulation and design of experiment (DOE) optimization techniques. Several applications of rolling contact were conducted and the parameters related to rollers’ materials, coating, temperature, and loads were investigated.

M50 steels (0.8C-4.2Cr-4.3Mo-1V wt.%) and 100CrMnMo8 steel (1.0C-2.0Cr-0.5Mo-1.0Mn-0.5Si wt.%) were analyzed with and without titanium nitride (TiN), zirconium nitride (ZrN) and tungsten carbide (WC) coatings under different temperature and loading conditions. Results showed that cracks propagation were limited to extreme load when using coating technology. A fully three-dimensional finite element model showed the Von Mises stresses and displacement under different temperatures. Findings confirmed that coating will enhance the lifetime of rollers and inhibit cracks and plastic deformation with better contribution from TiN under extreme pressure if compared to WC. DOE optimization of the parameter used in this study correlate closely with previous experiments and provided a solid conclusion of the best combination in rolling contact applications.

Commentary by Dr. Valentin Fuster
2018;():V009T12A037. doi:10.1115/IMECE2018-86621.

Battery separators are thin, porous membrane of 20∼30 microns thickness. Polymer separators display a significant amount of shrinkage at elevated temperatures. It is difficult to quantitatively characterize the large shrinkage behavior with a free standing separator sample. This paper examines the use of a dynamic mechanical analyzer under tensile mode in measuring the coefficient of thermal expansion (CTE) of three commonly used separators.

Commentary by Dr. Valentin Fuster
2018;():V009T12A038. doi:10.1115/IMECE2018-87929.

Thin films of titanium-silicon carbonitride (TiSiCN) with titanium adhesion layers were deposited at approximately 280°C on horizontally and vertically-mounted strips of 301-stainless steel by reactive magnetron sputtering. Considerable differences in the mid-deflections and radii of curvature between the vertical and horizontal samples were observed. Cross-sectional characterizations done on a TEM revealed a columnar growth and uniform microstructure. A finite-element model of the tri-layer sandwich structure using Mesh-Tie constraints was developed to estimate the intrinsic stress levels in the overcoat as probable functions of substrate location and orientation. The computational model in the absence of intrinsic stress was validated by analytical expressions for multilayer films. The initial stress state parameter was varied in Abaqus until consistency in curvature-values was achieved with the physical measurement obtained from an optical setup specially-constructed for this purpose. The difference in the S11/S22 principal stresses provided the intrinsic stress estimate. The calculated values of intrinsic stress were then applied to an FEA test model with fixed constraints to computationally determine the stress reduction for individual samples.

Commentary by Dr. Valentin Fuster
2018;():V009T12A039. doi:10.1115/IMECE2018-88420.

Journal bearing is one of the most important components for supporting high speed rotating machinery such as compressors and turbo machines. In recent trends, non-circular journal bearings (lemon bearing, three-lobe bearing, four-lobe bearing, etc.), for their greater load capacity and better stability, have become a superior choice and found wide spread application. In this paper, the nonlinear oil film force is expressed using the dynamic stiffness and damping of 1st-3rd order. And the film thickness and pressure are analyzed using Fourier method, so that the corresponding harmonic components and their deeper connection can be further explored. The paper shows that the nonlinear dynamic performances are connected closely with the bearings’ profile, and lays the foundation for expressing the precise nonlinear oil film force.

Commentary by Dr. Valentin Fuster

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

2018;():V009T12A040. doi:10.1115/IMECE2018-87236.

A new model for determining band gaps for elastic wave propagation in a periodic composite beam structure is developed using a non-classical Timoshenko beam model that incorporates the surface energy, transverse shear and rotational inertia effects. The Bloch theorem and transfer matrix method for periodic structures are employed in the formulation. The new model reduces to the classical elasticity-based model when the surface energy effect is not considered. It is shown that the band gaps predicted by the current model depend on the surface elastic constants of each constituent material, beam thickness, unit cell size, and volume fraction. The numerical results reveal that the band gap based on the current non-classical model is always larger than that given by the classical model when the beam thickness is very small, but the difference is diminishing as the thickness becomes large. Also, it is found that the first frequency for producing the band gap and the band gap size decrease with the increase of the unit cell length according to both the current and classical models. In addition, it is observed that the volume fraction has a significant effect on the band gap size, and large band gaps can be obtained by tailoring the volume fraction and material parameters.

Commentary by Dr. Valentin Fuster
2018;():V009T12A041. doi:10.1115/IMECE2018-87252.

Numerical and experimental studies performed to develop nanocomposites with varying carbon nanotube (CNT) alignment density within an epoxy matrix are presented. A 3-D numerical model has been developed that looks at the behavior of CNTs in epoxy resin subjected to non-uniform electric fields by explicitly accounting for electric field coupled with fluid flow and particle motion considering the transient resin viscosity. The transient nature of resin viscosity has been incorporated into the simulation study with data related to resin viscosity variation with time and temperature generated experimentally. The response of CNTs due to the induced dielectrophoretic force was studied using the numerical model. The model facilitated the design of an optimal electrode configuration for the processing of variable density composites. A computer controlled Arduino UNO based circuitry was developed to control supply of voltage to the electrodes during sample fabrication. The circuit was then integrated with AC voltage supply units and the electrode set-up for fabricating the variable density composite samples. Low weight fractions of CNTs (0.05 wt.% and 0.1 wt.%) in epoxy resin were used for the experimental work and preliminary experimental studies were conducted. Electrical characterization results of the variable density nanocomposites indicate over 100% and 30% increase in electrical resistance measured across sample widths in 0.05 wt.% and 0.1 wt.% CNT samples, respectively. The measured sample resistance values confirmed that variation in CNT alignment density was achieved across the samples.

Commentary by Dr. Valentin Fuster
2018;():V009T12A042. doi:10.1115/IMECE2018-87873.

The properties of the inclusions, viz. size, shape, and distribution significantly affect macroscopic properties of a polymer composite. Finite element (FE) modeling provides a viable approach for investigating the effects of the inclusions on the macroscopic properties of the polymer composite. In this paper, finite element method is used to investigate ultrasonic wave propagation in polymer matrix composite with a dispersed phase of inclusions. The finite element models are made up of three phases; viz. the polymer matrix, inclusions (micro constituent), and interphase zones between the inclusions and the polymer matrix. The analysis is performed on a three dimensional finite element model and the attenuation characteristics of ultrasonic longitudinal waves in the matrix are evaluated. The attenuation in polymer composite is investigated by changing the size, volume fraction of inclusions, and addition of interphase layer. The effect of loading frequency of the wave on the attenuation characteristics is also studied by varying the frequency in the range of 1–4 MHz.

Results of the test revealed that higher volume fraction of inclusions gave higher attenuation in the polymer composite as compared to the lower volume fraction model. Smaller size of inclusions are preferred over larger size as they give higher wave attenuation. It was found that the attenuation characteristics of the polymer composite are better at higher frequencies as compared to lower frequencies. It is also concluded that the interphase later plays a significant role in the attenuation characteristics of the composite.

Commentary by Dr. Valentin Fuster
2018;():V009T12A043. doi:10.1115/IMECE2018-88620.

The increasing demand for system miniaturization and high power density energy produces excessive thermal loads on electronic devices with significant mechanical strain. Carbon Nanotubes (CNTs) based devices are found to have excellent thermal transport properties that makes them attractive for thermal management of these miniaturized nano-electronic devices under extreme environments. These conductive nanostructure (carbon nanotubes, graphene, etc.) are often embedded in polymers or other high-strain alloys (the matrix phase), and are used as bridging materials for conductivity (electrical and thermal) with strain resiliency. The effect of strain on the thermal transport properties of these nanostructures have often been overlooked and will be the focus of this work. The thermal conductivity of the nanostructure is obtained in LAMMPS using the Heat-Bath method, which is a reverse non-equilibrium molecular dynamics (RNEMD) simulation strategy. In RNEMD, constant amount of heat is added to and removed from hot and cold regions and the resultant temperature gradient is measured. The effect of strain on the thermal conductivity of the single and multiwalled nanostructures of various configurations will be discussed with specific emphasis on the phonon density of states of nanotubes at different strain states.

Commentary by Dr. Valentin Fuster
2018;():V009T12A044. doi:10.1115/IMECE2018-88790.

Traumatic brain injury is one of the leading causes of injury and death in both developed and developing countries. Animal models are important preclinical tools for injury level studies. In this study, a finite element (FE) model of mouse brain was constructed to investigate the biomechanical responses of brain tissue during a controlled cortical impact (CCI). Impact of the brain tissue was simulated with varying impact speeds and angles. Computational results indicated that the viscoelastic properties of the brain tissue and the impact angle could greatly influence the injury responses. Comparison with the experimental observation showed that energy based stress parameters such as the von Mises stress has the potential to be descriptive of the injury levels.

Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures, and Fluids: Multiscale Modeling and Experimentation of Geomaterials

2018;():V009T12A045. doi:10.1115/IMECE2018-88257.

The fracture response of rock, a quasi-brittle material, is very sensitive to its microstructural defects. Herein, we use statistical volume elements (SVEs) to characterize rock fracture strength at the mesoscale, based on the distribution of microcracks at the microscale. The use of SVEs ensures that the material randomness is maintained upon “averaging” of microscale features. Certain fracture strengths, such as uniaxial tensile strength, uniaxial hydrostatic strength, shear strength, and uniaxial compressive strength, are obtained and characterized for different angles of loading. Thus, a material with anisotropic fracture strength can be characterized. Statistics of the characterized strengths are analyzed, as well as their auto- and cross-correlation functions of these random fields to shed light on the length scales, relative to the volume element size, at which homogenized properties vary. While crack interaction is not included, the analysis provides insight on the distribution and correlation of different strengths. Finally, the asynchronous spacetime discontinuous Galerkin method is used for macroscopic fracture analyses of two rock domains homogenized by SVEs.

Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures, and Fluids: Multiscale Models and Experimental Techniques for Composite Materials and Structures

2018;():V009T12A046. doi:10.1115/IMECE2018-86543.

Composites are prone to delamination damage when impacted by low velocity projectiles because of the poor through-thickness strength. Therefore, some of the problems with composites are their poor impact damage resistance, weak post-impact mechanical properties, and the difficulty to inspect the impacted area by nondestructive means. Damage characterization of composite materials requires a scientific methodology, knowledge of polymeric materials, and direct field experience. In this work, low-velocity impact response of composite laminates was experimentally studied using drop-tower to determine the energy absorption. Three types of composites were used: carbon fiber, glass fiber, and mixed fiber composite laminates. In addition, these composites were characterized using thermography to quantify their post impact damage. It was found with the 3D temperature distribution that a strong correlation can be determined between the measured temperatures at the impact region with the quantification of the damage using thermal imaging with advanced mid-wave camera.

Commentary by Dr. Valentin Fuster
2018;():V009T12A047. doi:10.1115/IMECE2018-87031.

In the last two decades, researchers have implemented two-dimensional (2D) Finite Element (FE) simulations of particle-reinforced composites for various purposes, including prediction of effective properties and failure modes. The present work aspires to examine the validity of the hypothesis that 2D FE simulations can provide accurate predictions for various thermomechanical properties of high volume fraction (VF) particle-reinforced composites. For this purpose, the random sequential adsorption (RSA) algorithm is implemented to generate FE simulations of various composites. The uniqueness in the methodology of the present work is in the generation of FE simulation of composites with more than two material types as reinforcement, as well as thorough and concurrent comparison of multiple thermal and mechanical properties. The adequacy of the simulations is verified statistically, and the results are compared to predictions from established schemes as well as certain experimental findings. These comparisons show that the predictive power of 2D FE simulations is lower for elastic properties, and higher for coefficient of thermal expansion (CTE) and thermal conductivity of particle-reinforced composites. The findings of this research can guide the researchers in making better decisions for implementing Finite Element Method (FEM) for designing high VF composites.

Commentary by Dr. Valentin Fuster
2018;():V009T12A048. doi:10.1115/IMECE2018-87106.

Robust design and analysis of carbon fiber reinforced polymers (CFRP) mandates a thorough understanding of the onset and propagation of damaging mechanisms. Damage can manifest from fiber tension, fiber compression, matrix tension, and matrix compression. Of these damage forms, matrix compression has seen the least attention. Previous work has developed experimental specimens that enabled characterization of the onset and propagation of matrix compression damage. However, if high performance composite materials are used complications can arise when the matrix compression strength (σMC) exceeds the matrix tension strength (σMT). When the σMCMT ratio is greater than 2, compact compression (CC) specimens can exhibit matrix tension damage before the onset of matrix compression damage. The onset of matrix tension damage prevents proper characterization of matrix compression damage mechanisms. This paper presents the development of a novel stepped compact compression specimen. The reduced thickness of the stepped region allows significant matrix-compression damage to occur prior to tensile failure. Specimens comprised of 90° plies were fabricated using either a machined taper or a layering process. Both methods were successful however variability in machining generated substantial inconsistency and layering was found to be superior.

Commentary by Dr. Valentin Fuster
2018;():V009T12A049. doi:10.1115/IMECE2018-87337.

Ceramic matrix composites (CMCs) are a promising subclass of composite materials suitable for high temperature applications. CMCs exhibit multiple damage mechanisms such as matrix cracking, interphase debonding, fiber sliding, fiber pullout, delaminations etc. Additionally, process induced defects such as matrix porosity exists at multiple length scales and has a considerable influence on the mechanical and failure behavior of CMCs. In the current work, the effect of intra-tow porosity, which exist at the micro-scale, on the mechanical behavior of CMCs has been investigated by numerical homogenization.

Micro-scale response of 3 phase CMCs with intra tow pores has been obtained by finite element analysis based homogenization. Pores have been modeled as non-intersecting ellipsoids in a square unit cell representative of matrix material. The effective mechanical properties of porous matrix at the micro scale has been obtained from numerical homogenization, which are in good agreement with Mori-Tanaka mean field theory. The obtained matrix elastic properties have then been included in a three phase unit cell consisting of fiber, interphase and matrix representative of CMC microstructure. The effect of porosity volume fraction and aspect ratio on the effective elastic properties of the composite have been reported. Homogenization approach to model statistical distribution of pore size obtained from X-ray computed tomography of CMC minicomposite has been proposed.

Commentary by Dr. Valentin Fuster
2018;():V009T12A050. doi:10.1115/IMECE2018-87459.

Unit-cell modelling is one of the useful methods to analyze deformation in periodic structures like honeycombs, perforated boards, and woven fabrics. The initial state of the structures is considered to be stress-free in ordinal deformation analysis, but in actual practice, the analysis is difficult, because initial stresses like assembly stress and residual stress need to be considered, as they are known to affect the results. In this study, a technique of taking into account the initial-stress state in woven fabrics is discussed, which has resulted in the establishment of a precise design method for textiles. LS-DYNA, which is a general-purpose finite element (FE) software, has been utilized to simulate the complex deformations in woven fabrics. In this software, a function of the global constraint on boundary conditions facilitates the analysis of periodic structures, but causes difficulties in computing the initial stress states in woven fabrics, as the conditions of mechanical equilibrium have to be satisfied in the governing equations. In particular, duplicated definitions of forced displacement and periodic deformation make the computation impossible, hence, a phantom-element has been introduced to ease the FE analysis by defining these quantities. A unit-cell of the woven fabric is identified and the initial states in stressed conditions can be estimated for periodic structures of plain-woven fabrics by a periodic-analysis technique of LS-DYNA coupled with the phantom-element, which yields a weaving motion of the yarn in plain-woven fabrics.

Commentary by Dr. Valentin Fuster
2018;():V009T12A051. doi:10.1115/IMECE2018-87636.

Transverse shear moduli of the sandwich core and flexural stiffness of all-composite sandwich constructions are determined with three-point beam bending tests, and compared with the analytical and finite element analysis solutions. Additionally, Digital Image Correlation (DIC) system is employed to validate the experimental results by monitoring the displacements. The effect of orientation of the composite core material with respect to the beam axis on the shear modulus of the core material itself, flexural stiffness of the sandwich beam, maximum loading, and the maximum stresses on the sandwich panel are also examined. Comparable results are achieved through experiments, finite element and analytical analyses.

Commentary by Dr. Valentin Fuster
2018;():V009T12A052. doi:10.1115/IMECE2018-87966.

In desert environment, wind turbines blades undergo severe erosion process caused by air-borne sand particles. The erosion damage on blade surface is sensitive to particles velocity, mass flux and impingement angle. The objective of the present work is to get insight into the underlying mechanics of damage evolution by erodent particles in coated Glass Fiber Reinforced Polymer (GFRP) at different impingement angles within the framework of Discrete Element Method and Finite Element (DEM-FE). This paper presents a novel experimental technique to measure sand particles velocity which is then compared to Computational Fluid Dynamics (CFD) simulations based on Eulerian-Eulerian multiphase flow model. The computed sand solid phase velocity and mass flux were used into the DEM-FE analysis to investigate the erosion damage on the coated GFRP surface at multiple impingement angles. Primary findings of CFD show strong dependence between sand particles velocity and its volume fraction. DEM-FE results showed that, the evolution of eroded surface is strongly dependent on the particles impingement angle; in normal impact, the maximum material removal occurs initially, and in oblique impact there is a gradual removal of material along the erosion process.

Commentary by Dr. Valentin Fuster
2018;():V009T12A053. doi:10.1115/IMECE2018-88249.

To accurately simulate fracture, it is necessary to account for small-scale randomness in the properties of a material. Apparent properties of Statistical Volume Elements (SVE), can be characterized below the scale of a Representative Volume Element (RVE). Apparent properties cannot be defined uniquely for an SVE, in the manner that unique effective properties can be defined for an RVE. Both constitutive behavior and material strength properties in SVE must be statistically characterized. The geometrical partitioning method can be critically important in affecting the probability distributions of mesoscale material property parameters. Here, a Voronoi tessellation based partitioning scheme is applied to generate SVE. Resulting material property distributions are compared with those from SVE generated by square partitioning. The proportional limit stress of the SVE is used to approximate SVE strength. Superposition of elastic results is used to obtain failure strength distributions from boundary conditions at variable angles of loading.

Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures, and Fluids: Peridynamic Modeling of Materials: Behavior

2018;():V009T12A054. doi:10.1115/IMECE2018-86129.

Peridynamics ability to model crack as a material response removes deficiencies associated with using classical continuum-based methods in modeling discontinuities. Due to its nonlocal formulation, however, peridynamics is computationally more expensive than the classical continuum-based numerical methods such as finite element method. To reduce the computational cost, peridynamics can be coupled with finite element method. In this method, peridynamics is used only in critical areas such as the vicinity of crack tip and finite element method is used everywhere else. The main issue associated with such coupling methods is the spurious wave reflections occurring at the interface of peridynamics and finite elements. High frequency waves traveling from peridynamics to finite element spuriously reflect back at the interface and the amplitude of transmitted waves also alter. In this paper, we take an analytical approach to study this phenomenon of spurious reflections. We study the impact of factors such as horizon size of peridynamic formulation, discretization, and change in mesh size on the amplitude of spuriously reflected waves. Finally, we present a method to reduce these spurious reflections by using Arlequin method.

Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures, and Fluids: Quantitative Visualization of Fracture and Failure

2018;():V009T12A055. doi:10.1115/IMECE2018-87368.

The change of the lath martensitic structure in the modified 9Cr-1Mo steel was observed in the specimens after the intermittent fatigue and creep tests using EBSD (Electron Back-Scatter Diffraction) analysis. The Kernel Average Misorientation (KAM) value and the image quality (IQ) value obtained from the EBSD analysis were used for the quantitative evaluation of the change in the lath martensitic texture. It was found that the lath martensitic texture started to disappear clearly after 107–108 cycles under the fatigue loading at temperatures higher than 500°C when the amplitude of the applied stress exceeded a critical value. Similar change also appeared in the creep test. The critical value decreased monotonically with the increase of the test temperature. This microstructure change decreased the strength of the alloy drastically.

In order to explicate the dominant factors of the change quantitatively, the changes of the microstructure and the strength of the alloy were continuously measured by applying an intermittent creep test at elevated temperatures. It was found that the effective activation energy of atomic diffusion decreased drastically under the application of mechanical stress at elevated temperatures. The effective diffusion length for the disappearance was about 9 μm, and this value was much larger than the initial pitch of the lath martensitic texture of about 0.5 μm, and smaller than the average size of the initial austenite grains of about 20 μm. Therefore, the stress-induced acceleration of atomic diffusion was attributed to the disappearance of the initially strengthened micro texture. The change of the micro texture caused the drastic decrease in the yielding strength of this alloy. Finally, the prediction equation of the lifetime of the alloy was proposed by considering the stress-induced acceleration of atomic diffusion under the application of mechanical stress at elevated temperatures.

Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures, and Fluids: Symposium on Modeling of the Fracture, Failure, and Fatigue in Solids

2018;():V009T12A056. doi:10.1115/IMECE2018-87801.

The bottom hole assembly (BHA) of a modern drill string for directional drilling mainly comprises a drill bit, a rotary steerable system, and a measurement while drilling tool. The tools and subs used on a BHA are screwed together through rotary shouldered threaded connections. Each connection is made up with a pin and a box. These connections are the weakest links when the BHA undergoes a large number of revolutions in a curved well section. When the fatigue life of a connection is consumed during a drilling job, a twist-off would occur, which could result in an enormous amount of non-productive time and possibly loss of the bottom BHA section in the hole. Cold rolling has proven to be able to improve fatigue resistance of a threaded connection by pressing a rolling wheel against the thread root and generating a layer of compressive residual stress at the root. Understanding how cold rolling improves fatigue resistance of a threaded connection is important for optimization of the rolling parameters and prediction of the BHA service life in a given drilling condition.

In this paper, a predictive method is presented for fatigue life of a cold rolled threaded connection. A finite element model was developed to simulate the cold rolling process. The resulting deformation and stress states at the root were carried over through makeup of the pin and the box as well as through cyclic bending of the connection. The fatigue life predictions were found to be in favorable agreement with the experimental measurements from full-scale fatigue tests at different bending moment levels applied.

Topics: Fatigue life
Commentary by Dr. Valentin Fuster
2018;():V009T12A057. doi:10.1115/IMECE2018-88429.

Maintaining material inhomogeneity and sample-to-sample variations is crucial in fracture analysis, particularly for quasibrittle materials. We use statistical volume elements (SVEs) to homogenize elastic and fracture properties of ZrB2-SiC, a two-phase composite often used for thermal coating. At the mesoscale, a 2D finite element mesh is generated from the microstructure using the Conforming to Interface Structured Adaptive Mesh Refinement (CISAMR), which is a non-iterative algorithm that tracks material interfaces and yields high-quality conforming meshes with adaptive operations. Analyzing the finite element results of the SVEs under three traction loadings, elastic and angle-dependent fracture strengths of SVEs are derived. The results demonstrate the statistical variation and the size effect behavior for elastic bulk modulus and fracture strengths. The homogenized fields are mapped to macroscopic material property fields that are used for fracture simulation of the reconstructed domain under a uniaxial tensile loading by the asynchronous Spacetime Discontinuous Galerkin (aSDG) method.

Commentary by Dr. Valentin Fuster

Mechanics of Solids, Structures, and Fluids: Symposium on Multiphyics Simulations and Experiments for Solids

2018;():V009T12A058. doi:10.1115/IMECE2018-87414.

In gas turbines, the blade vibration caused by aerodynamic excitation or by self-excited vibration and flutter leads to high cycle fatigue that represents the main cause of damage in turbomachinery. Turbine operators have resorted to assess the blade vibrations using non-contact systems. One of the well-known non-contact methods is Blade Tip Timing (BTT). BTT is based on monitoring the time history of the passing of each blade tip by stationary sensors mounted in a casing around the blades. The BTT method evaluates the blade time of arrival (ToA) in order to estimate the vibration. To perform the BTT technique, optical sensors were widely used by industry due to their high accuracy and performance under high temperatures, but the main drawback of these systems is their low tolerance to the presence of contaminants. To mitigate this downside, Eddy Current Sensors (ECS) are a good alternative for health monitoring application in gas turbines due to their immunity to contaminants and debris. This type of sensor was used by many researches, predominantly on the experimental side. The focus was to extract response frequencies and therefore the accuracy of the timing measurement was ignored due to the lack of modeling. This paper fills the gap between experiments and modeling by simulating a BTT application where detailed finite element modeling of active and passive ECS outputs was performed. A test rig composed of a bladed disk with 12 blades clamped to a rotating shaft was designed and manufactured in order to validate the proposed models with experimental measurements. Finally, a comparison between these different types of sensor output is presented to show the effect of the blade tip clearance and rotational speed on the accuracy of the BTT measurement.

Commentary by Dr. Valentin Fuster
2018;():V009T12A059. doi:10.1115/IMECE2018-88627.

The viscoelastic properties of rubbers play an important role in dynamic applications and are commonly measured and quantified by means of Dynamic Mechanical Analysis (DMA) tests. The rubber properties including the static and dynamic moduli are a function of temperature; and an increase in the temperature leads to a decrease in both moduli of the rubber. Due to the heat generation inside the rubber during the DMA test and the possible change of the rubber properties it is important to quantify the amount of temperature rise in the rubber specimen during the test. In this study, a Finite Element Analysis (FEA) model is used to predict the heat generation and temperature rise during the rubber DMA tests. This model is used to identify the best shape of the specimen to achieve the minimum increase in temperature during the test. The double sandwich shear test and the cyclic compression tests are considered in this study because these two tests are mostly used in industry to predict the rubber viscoelastic properties.

Topics: Heat , Rubber , Testing
Commentary by Dr. Valentin Fuster

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