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Materials

2006;():1-6. doi:10.1115/IMECE2006-14147.

Hyperthermia (HT) is a cancer treatment that utilizes a variety of heating methods to destroy cancerous tumors. A diversity of technical problems still exists regarding HT's different approaches, therapeutic potential, and evidence of effectiveness. The foremost problem is in generating and controlling heat in tumors to target cancer sites. The window of temperature for HT is between 42°C and 45°C, with the literature suggesting 43°C to be the ideal temperature for inducing apoptosis (programmed cell death). Normal cells undergo necrosis at higher temperatures than that of the specified range. To address control problems, various methods have been utilized to localize HT heating and limit its temperatures through various applicators, materials, and procedures. One method has been to implant various materials into the human body to heat tumors, a process known as Magnetic Hyperthermia (MH) as it uses magnetic nanoparticles (NP). This method is particularly useful for sending thermal energy to deep seated tumors by using ferro/ferri magnetic NP that absorb non-ionizing electromagnetic (EM) fields delivered into the human body externally. These NP have been shown to heat surrounding tissue until they reach a Curie temperature (Tc ) at which generated heat is minimized (many thermodynamic properties change at Tc , such as dielectric, elastic, optical and thermal properties. Fabricated NP, due to spontaneous polarization, can heat via hysteresis losses under applied EM fields making them candidates for testing in (EM) HT systems. Various ferro- and ferromagnetic materials have been studied extensively by this group (e.g.: Ni-Cu, Ni-Co, Ni-Cr, Er, Ce, Gd, and their alloys, etc.) as candidates for HT due to their production of heat through hysteresis or magnetic spin mechanisms. With the use of these nanoparticle systems, the focus of this paper is to produce analysis of heat generation through electromagnetic energy conversion for magnetic hyperthermia cancer treatment and to investigate the heat transfer and heat generation of magnetic NP due to temperature rise upon application of externally applied AC magnetic field. Both, polarization switching and inhomogenities affect polarization orientation within a crystal. Domain switching occurs in two steps: first, the domain nucleates at critical level of applied EM field; second, the interface between the two domains propagates. Particles moving across the interface transform from one domain type to another, which leads to a release of energy in the form of heat. This, in turn, leads to a temperature rise at the interface.

Commentary by Dr. Valentin Fuster
2006;():7-11. doi:10.1115/IMECE2006-14219.

Pulsed laser deposition (PLD) is a popular technique for creating thin films. The film characteristics are directly related to the kinetic energy of the laser-induced plume. According to the theory of transient shock wave expansion during laser ablation, laser-induced plume properties are strongly affected by laser intensity as well as ambient temperature, pressure, and gas species. This theory leads to the development of PLD strategies to properly optimize the PLD parameters. The experiments were carried out to deposit diamond-like carbon (DLC) thin films under different ambient temperature, pressure and gas species. The deposited DLC thin films were characterized by Raman spectroscopy. Experimental results showed that the thin film quality can be improved by decreasing the ambient temperature, increasing the ambient pressure and using ambient gases with low molecular weight. Experimental results agree well with the theoretical prediction.

Commentary by Dr. Valentin Fuster
2006;():13-20. doi:10.1115/IMECE2006-14998.

Recent research has shown that the flow stress necessary to deform certain metallic materials can be decreased when an electrical current is present in the material while undergoing deformation. As part of this testing, it was found that, under higher current densities, the various metals began to exhibit strain weakening and superplastic behavior (i.e., the stress either remained constant or decreased as the strain increased). During typical compression testing, it is expected that the stress will continually increase as the strain increases. This is due to the increase in the cross-sectional area of the test specimen as well as the frictional effects that are present between the specimen and the fixture throughout the test. Since this strain weakening and subsequent superplastic behavior is opposite of what typically occurs during normal low temperature compression tests, it introduces a new electrical current-related phenomenon. This paper contains a detailed investigation of superplastic behavior using experimental results, focusing on 6A1-4V Titanium in particular. To examine this phenomenon, compression tests are run at different current densities. Some tests are conducted with the electricity present the entire time, while other tests are conducted with the electricity turned off at various points within the superplastic region. Still other tests have a pulsed electrical current present. It will be shown that the superplastic behavior allows significant increases in total deformation to be achieved using extremely low forces.

Commentary by Dr. Valentin Fuster
2006;():21-24. doi:10.1115/IMECE2006-15974.

A mechanical pressure injection technique has been developed to fabricate uniform metallic nanowires in the pores of anodic aluminum oxide (AAO) template. The AAO template was prepared from general purity aluminum by a two-step anodization followed by heat treatment to achieve highly ordered nanochannels. The nanowires were fabricated by an injection process using a hydraulic pressure method. A mold containing the AAO template and a metal foil was placed inside a vacuum chamber and heated up to the melting temperature of the given metal using a hot plate. The hot chamber was then removed from the hot plate and pressure was applied on the melt through the sliding column of the chamber, using a hydraulic jack to impregnate the molten metal into the nanochannels of the AAO. The nanowires were found to be dense and continuous with uniform diameter throughout their length. Diffraction experiment in the transmission electron microscope revealed that individual nanowires are single crystalline. This paper will present the fabrication process of the AAO template, and the fabrication of Bi nanowires as well as their characterization conducted using SEM, TEM, XRD and DSC.

Commentary by Dr. Valentin Fuster
2006;():25-32. doi:10.1115/IMECE2006-16247.

Scanning electron microscopy and high-resolution electron backscatter diffraction (EBSD) have been used to study the texture and microstructure evolution during the crystallization of initially amorphous GaAs thin films. A KrF excimer laser, with 30 ns pulse duration was used for crystallization of a-GaAs grown on SiO2 Substrate using molecular beam epitaxy (MBE) technique. The effect of laser energy density and film thickness on grain morphology has been studied. The integrated information on grain size distribution, preferred orientation, and nature of grain boundaries provides useful information to postulate the mechanism of grain-growth and likely role of different contributing parameters in the evolution of final texture under the highly transient processing conditions prevailing during the short laser irradiation. The results show that for thick films the laser crystallization results in a weak <111> fiber texture. While for a thinner films the grains have a strong <001> texture that strengthens with a decrease in film thickness and increase in laser energy density.

Commentary by Dr. Valentin Fuster
2006;():33-38. doi:10.1115/IMECE2006-16277.

The low carbon alloy steel was single face treated by a special hot diffusion method, and thus the gradual composite steel was produced. The microstructures of composite steel were very different from the matrix steel, white layer speared near the treated surface, and nano- and sub-micron particles were existed in the white layer. The results of ramon spectrum test indicated that the nano- and sub-micron particles can transfer several millimeters, several centimeters or even more. The mechanical properties changed sharply compared with the matrix steel. The hardness and the tensile strength near the treated surface were much higher than the matrix steel, and decreased gradually with the increase of distance to the treated surface. The composite steel has high strength, high hardness, high wear-resistance, high corrosion-resistance and etc. From the engineering application point of view, this technique can be used to produce super high qualities alloy steels, which can be used to the field as: metallurgy, mine, automobile, manufacture, energy sources, and etc.

Commentary by Dr. Valentin Fuster
2006;():39-43. doi:10.1115/IMECE2006-13783.

Inclusion of nano-sized alumina by the surface treatment of S2 fiberglass (fiber modification) or ultrasonically exfoliated in epoxy resin system (resin modification) has been shown to provide epoxy-fiberglass hybrid composite systems with changes in their mechanical/ damage behavior under static tensile loading conditions. Integration of alumina nano-particles in epoxy-S2 fiberglass to form hybrid composites has not only shown improvements in the material properties, but also changes in the failure mechanism of the material system. This phenomenon is influenced by the changes in constituent interaction and its load transfer mechanism. In the processing of these hybrids composite systems, alumina nano-particles (sized at 110nm) are functionalized and grafted into epoxy composite material system during material processing via resin solution treatment and fabric surface treatment. These alumina embedding methodologies to form hybrid composites employed are the resin modification and fiber modification in conjunction with the conventional vacuum assisted resin transfer molding (VARTM) process for the manufacture of composite laminates. The chemical bonding and adhesion between the inorganic alumina and the organic resin is also enhanced via the functional treatment of the alumina particles with a coupling agent in the form of tris-2-methyoxyethoxy vinylsilane- T2MEVS (silane coupling agent). Processing methodologies are used to fabricate particulate reinforcement for various (<5%wt) compositions. Performance evaluation is carried to study the effect of the nano-particulate alumina on mechanical properties. Thermo-physical properties changes caused by particulate inclusion in hybrid material matrix phase are studied via Differential Scanning Calorimetry (DSC) and are also discussed.

Commentary by Dr. Valentin Fuster
2006;():45-57. doi:10.1115/IMECE2006-14422.

Vacuum Assisted Resin Transfer Molding (VARTM) is used to produce high quality composite parts at lower cost than other manufacturing methods. However, traditional VARTM injection methods are incapable of accounting for variations in preform permeability within a mold. As a result, creating complex components is a labor intensive and expensive process often requiring a trial and error approach to insure complete infusion of the preform fibers. To address this limitation, a new system for delivering resin to a VARTM mold using a series of ports in the tooling surface rather than traditional injection lines has been developed. A port injection process has been designed that utilizes a closed loop control system of ports and sensors built into the mold. Finite element models of this new process indicate complete infusion can consistently be achieved, even for mold lay-ups with large variations in permeability. Results indicate the system is capable of identifying and accounting for preform variability, and correctly delivering resin to low permeability regions usually unfilled with conventional VARTM. In addition, this new technique significantly reduces lay-up time and total time to infuse a part. Experiments with a prototype lab-scale mold have been used to validate the performance of this new injection process. Unlike a conventional VARTM setup, the innovative port injection process can deliver resin to any location within the mold, thus reducing the potential for dry regions and improving part quality and consistency.

Commentary by Dr. Valentin Fuster
2006;():59-63. doi:10.1115/IMECE2006-14924.

Alumina is a widely used ceramic material due to its high hardness, wear resistance and dielectric properties. The study of phase transformation and its correlation to the mechanical properties of alumina is essential. In this study, interfacial adhesion properties of alumina thin films are studied using cross-sectional nanoindentation (CSN) technique. Alumina thin films are deposited at 200 and 700 °C, on Si (100) substrates with a weak Silica interface, using pulsed laser deposition (PLD) process. Effect of annealing on the surface morphology of the thin films is studied using atomic force microscopy. Xray diffraction studies revealed that alumina thin films are amorphous in nature at 200 °C and polycrystalline with predominant gamma alumina phase at 700 °C.

Commentary by Dr. Valentin Fuster
2006;():65-69. doi:10.1115/IMECE2006-15022.

Thin films of SrCe0.95 Y0.05 O3 have been successfully prepared on Si(100) substrates using flame-assisted chemical vapor deposition. XRD characterization shows the inclusion of fluorite phase of CeO2 in the perovskite phases, which may be caused by strontium depletion during deposition. The effects of total-metal concentration in the solution and substrate temperature on the surface morphology and think thickness growth of the coatings have been explored. It was found that both the intermediate concentration and temperature produces smoothest films and increasing the concentration had more significant effect on enhancement of the film thickness growth.

Commentary by Dr. Valentin Fuster
2006;():71-77. doi:10.1115/IMECE2006-15040.

The characteristics of the Ni/YSZ anode material for the solid oxide fuel cells (SOFCs) were investigated in order to study the relation between the porosity and the conductivity of the cell. Response Surface Methodology (RSM) was used for the study. The anode material was prepared with NiO and YSZ along with the graphite as pore former. The experiments were performed based on a central composite design matrix, which yielded nine sets of experiments. Porosity and conductivity measurements were performed on the sintered and reduced anode material. Using the measured values as output variables, statistical analysis was performed. The results indicated that the porosity increases by reducing the sintering temperature values, while the conductivity values were on the reverse scale. The conductivity values increase with increasing temperature. Using RSM technique, a ideal point was found in order to obtain a desired porosity volume and conductivity value.

Commentary by Dr. Valentin Fuster
2006;():79-84. doi:10.1115/IMECE2006-15133.

This study investigates the effect of exposure to elevated temperatures on the mechanical properties and moisture absorption kinetics of a graphite/epoxy composite laminate. 16-ply unidirectional AS4/3501-6 laminates are cured in an autoclave. The temperature profile during cure cycle involves a ramp of 5°C/min followed by a 3-hour hold at 177°C (350°F). The test samples obtained from these laminates are subjected to 150, 200, 250, 275, 300 and 325°C for 30min. Flexural strength and stiffness of the samples are characterized by three-point bending tests before and after the temperature exposure. These samples are then immersed into distilled water at 80°C and weighed at regular intervals to characterize their moisture absorption kinetics. Stiffness remained nearly unaffected from exposure to elevated temperatures except for 300 and 325°C. At 300 and 325°C, up to 21% and 58% reductions in flexural stiffness with respect to the control samples is observed, respectively. On the other hand, flexural strength displayed slight reduction at 250°C and resulted in over 60% and 88% deterioration for 300 and 325°C, respectively. Exposure to 150 and 200°C did not result in significant changes in mechanical properties. However, moisture absorption experiments indicated an increase in the rate of diffusion even if the mechanical properties are unaffected. The diffusion coefficient displayed an increase of 27% for 150°C, 75% for 200°C, reaching a maximum increase of 600% for 300°C exposure.

Commentary by Dr. Valentin Fuster
2006;():85-88. doi:10.1115/IMECE2006-15230.

Preparation of nanocrystalline titanium oxide particles by wet chemical method and the separation of these particles by gravitational sedimentation were investigated. A colloidal form of titanium oxide was synthesized by the reaction between titanium fluoride containing solution and hydroxyl ions in an aqueous medium under controlled conditions. Colloidal precipitates produced by this reaction can have different size particles. This titanium oxide suspension was separated using a large liquid column in which different size particles can be collected in different region of the column. Raman and X-ray diffraction were used to investigate the structural properties of these nanocrystalline titanium oxides. The properties of asproduced particles were compared with the properties of annealed samples at different temperatures. As-produced particles had the anatase structure while it was not changed when annealed below 700 °C. High temperature (>700 °C) annealed particles had the rutile structure. The grain size of asproduced samples was varied in the range of 7–90 nm. This study with titanium oxide as the model material indicates that the gravitational sedimentation is a very promising technique to separate a mixture of different size nanoparticles.

Commentary by Dr. Valentin Fuster
2006;():89-96. doi:10.1115/IMECE2006-15428.

The fiber-matrix interface between ceramic fibers and ceramic matrix plays a major role in the fatigue properties and toughness of continuous fiber reinforced ceramic matrix composites (CMCs). Boron Nitride (BN) is a widely used fiber coating material that provides a weak bond between the fiber and matrix. A weak fiber-matrix interface increases the strength and toughness of the overall CMC. Single fiber push-out tests were performed to study interfacial shear strength as a main parameter defining fatigue properties and toughness of SiC/SiC composites. The fiber-matrix interfacial shear strength was studied in melt infiltrated Hi-Nicalon/BN(CVI)/SiC composites exposed to various temperature and loading conditions, similar to those that are used in actual applications. Hi-Nicalon fibers with diameters of 13-14.5 μm were pushed out from samples with thicknesses ranging from 125-280 μm using a spherical tip with a 1 μm radius and 90° conical shape. Interfacial shear strength was calculated from sliding load, fiber diameter and sample thickness. Due to significant scattering, 30 individual push tests in every sample were used to obtain the average interfacial shear strength. The virgin sample has a shear strength of 20 MPa which is higher than tensile tested samples (12 MPa). Annealing of a virgin specimen for 100 hours at 1000°C slightly increased shear strength up to 21.5 MPa while annealing at 1100°C and 1200°C led to significant increase of shear strength up to 29 and 39 MPa correspondingly. This effect is associated with BN degradation at temperatures >1000°C.

Commentary by Dr. Valentin Fuster
2006;():97-103. doi:10.1115/IMECE2006-16193.

Thermal spray coating is being studied as one of the techniques used for coating graphite reinforced polymer composites, which are extensively used in the aviation industry. These coatings are studied for improvement of surface properties such as erosion resistance, UV protection, property retention and electro magnetic shielding. NiAl (63:35) (65%Ni,35%Al) intermetallic, NiAl (95:5) (95%Ni,5%Al), Aluminum and Zinc coating were thermal-spray deposited using different procedures (plasma, flame, electric wire arc) onto composite specimens. Two categories of coating were evaluated: Coatings with bond coating and coatings without bond coating. These coatings were tested for protection against erosion encountered by aircraft components. The microstructures and micro-hardness of these coatings were determined. The bond strength between the substrate and the coating layer was evaluated by means of adhesion tests. The results obtained are discussed, with special attention being paid to the specific characteristics of the different spraying procedures.

Commentary by Dr. Valentin Fuster
2006;():105-110. doi:10.1115/IMECE2006-14877.

The bone-like carbonate apatite (BLCA) coatings can be coated biomimetically in the polymer surfaces by soaking in the simulated body fluid (SBF). This SBF contains similar ionic constituents to human blood plasma. Micro-porous 3D poly(lactic-co-glycolic acid) PLGA scaffolds were fabricated by the solvent casting/salt leaching technique using chloroform to dissolve the polymer. We accelerated the deposition of mineral on scaffolds for 1-2 days, modifying the mineralization process using surface treatments and 5x SBF. These scaffolds were analyzed by Scanning Electron Microscopy (SEM), Fourier Transform Infra-Red (FTIR) and X-ray Diffraction (XRD). The scaffolds coated with BLCA layer were placed in the 24 well plates containing 2 ml of media, such as Tris Buffered Saline-pH 7.4, cell culture media containing αMEM supplemented with 10% FBS, and 1% penicillin-streptomycin and incubated at 37°C for 21 days. The BLCA layer on surfaces of scaffold was stable even after 21 days immersed in Tris Buffered Saline and cell culture media. This study suggests that BLCA were stable for at least 3 weeks in the both media, and therefore, mineral has a potential to use as a carrier for biological molecules for localized release applications as well as bone tissue engineering applications.

Topics: Biomimetics , PLGA
Commentary by Dr. Valentin Fuster
2006;():111-116. doi:10.1115/IMECE2006-15906.

The problem of the characterization of the solution properties of water soluble polymers is long-standing. These polymers tend to form aggregated supramolecular gels that are resistant to molecular dispersion. These materials are being widely used in a variety of industrial applications. Their principle functions are as rheological modifiers, where they thicken or gel solutions in products such as hair-care, detergents, air fresheners and foods; as flocculants for particle separation as applied to water clarification, sewage, and effluent treatment, and as stabilizers to control the properties of concentrated suspension and emulsions, for example in paints, pesticides, dyes, and pharmaceutical industries. Therefore it is important to understand their rheological properties under various operating conditions such as stress, strain, temperature etc, which will induce gelation. The rheological properties of starch gels of high concentration (up to 86% starch) have been investigated before [1]. In this paper we have investigated experimentally the shear viscosity and viscoelasticity properties of saline and polysaccharide suspensions at various low concentrations and pH at different temperatures using controlled stress and strain rheometers (Vilastic-3 and AR 2000). The data were then fitted with the power law and Cross model for low and higher concentrations respectively. The present results show that the viscosity/elasticity does not significantly change for low concentrations at different pH values. The maximum viscosity/elasticity was obtained around pH 5-7.4 at higher concentrations.

Commentary by Dr. Valentin Fuster
2006;():117-123. doi:10.1115/IMECE2006-14392.

A mathematical model to predict the nucleation and cell growth during the microcellular injection molding without mold, was developed. The nucleation equation, energy equation, equation of cell growth, and equation of gas content were solved numerically. The predicted nuclei density and cell diameter were compared with the experimental results. The experimental equipment including a conventional injection molding machine, specially designed nozzle, and supercritical fluid conveying system, is used to validate the predicted results. The polymer-gas solution ejected from the injection molding machine was foamed in nozzle and cooled in the air, rather than in the mold.

Commentary by Dr. Valentin Fuster
2006;():125-129. doi:10.1115/IMECE2006-14996.

This paper presents an efficient method for simulating the bone remodeling procedure. This method is based on the trajectorial architecture theory of optimization and employs a truss-like model for bone. The truss was subjected to external loads including 5 point loads simulating the hip joint contact forces and 3 muscular forces at the attachment sites of the muscles to the bone. The strain in the links was calculated and the links with high strains were identified. The initial truss is modified by introducing new links wherever the strain exceeds a prescribed value; each link undergoing a high strain is replaced by several new links by adding new nodes around it using the Delaunay method. Introduction of these new links to the truss, which is conducted according to a weighted arithmetic mean formula, strengthens the structure and reduces the strain within the respective zone. This procedure was repeated for several steps. Convergence was achieved when there were no critical links remaining. This method was used to study the 2D shape of proximal femur in the frontal plane and provided results that are consistent with CT data. The proposed method exhibited capability similar to more complicated conventional nonlinear algorithms, however, with a much higher convergence rate and lower computation costs.

Topics: Density , Muscle
Commentary by Dr. Valentin Fuster
2006;():131-140. doi:10.1115/IMECE2006-15212.

In this study, the effects of processing parameters on the cellular morphologies and mechanical properties of TPO70 (Thermoplastic Polyolefin) microcellular foams are investigated. Microcellular closed cell TPO70 foams were prepared using a two-stage batch process method. The microstructure of these foamed samples was controlled by carefully altering the processing parameters such as saturation pressure, foaming temperature and foaming time. The foam morphologies were characterized in terms of the cell density, foam density and average cell size. Elastic modulus, tensile strength, and elongation at break of the foamed TPO70 samples were measured for different cell morphologies. The findings show that the mechanical properties were significantly affected by the foaming parameters which varied with the cell morphologies. The experimental results can be used to predict the microstructure and mechanical properties of microcellular polymeric TPO70 foams prepared with different processing parameters.

Commentary by Dr. Valentin Fuster
2006;():141-146. doi:10.1115/IMECE2006-15240.

Constitutive modeling of stress-strain relationship of open-celled PLGA 85/15 foams under compression was studied. A constitutive model for compressive behavior was directly derived from the morphology of a unit cubic cell. These constitutive equations describe the stress-strain relationship as a function of the foam's material properties and cell morphology, such as elastic modulus, yield stress, relative density, cell strut thickness, and cell size. To verify this model, uniaxial compression testing was performed on foam samples. Using the gas foaming/salt leaching method, the samples were prepared by using different foaming parameters such as salt/polymer mass ratio, saturation pressure, and saturation time. The comparisons of theoretical and experimental data demonstrate that the constitutive model using a cubic unit cell accurately describes the behavior of PLGA foams with low relative densities under compression.

Topics: Modeling , Compression , PLGA
Commentary by Dr. Valentin Fuster
2006;():147-153. doi:10.1115/IMECE2006-15374.

Most of the existing fabrication techniques for tissue engineering scaffolds require the use of organic solvents that may never be fully removed even after long leaching hours. The residues of these organic solvents may reduce the ability of biological cells to form new tissue. In this study, interconnected porous structures were created using solid-state foaming and ultrasound. The interconnectivity was verified with dye test. The pore sizes of the foams ranged from 300 to 500 μm. Permeability measurements were also performed to quantify the interconnectivity using a system developed in house. The achieved average permeability of PLA foams with 300 μm pore size is 3.1×10-12 m2 . The bigger the closed pores are, the easier ultrasound can make them open. There is an optimum temperature range in which ultrasound will enhance the interconnectivity of the solid-state foam the most efficiently. An ultrasound cavitation model was proposed as the dominant pore opening mechanism and was used to explain the temperature effects and pore size effects. The combined solidstate foaming and ultrasound processing provides a way to fabricate porous polymer for potential tissue engineering applications.

Commentary by Dr. Valentin Fuster
2006;():155-157. doi:10.1115/IMECE2006-15789.

Fracture toughness of the rigid, low-density, closed-cell, polyurethane, foam used for insulation on the Space Shuttle External Tank is investigated. Data were obtained by loading double-edge-notched specimens in tension. To account for the anisotropic nature of the foam, two types, of specimens were tested so as to represent fracture properties along two different material directions. Additionally, for each type of specimen, two different notch sizes were tested.

Commentary by Dr. Valentin Fuster
2006;():159-167. doi:10.1115/IMECE2006-16173.

A recent surface energy estimation method [1] interpreting contact angle hysteresis measurements was used to estimate surface energy of various commercially important polymer films including UV radiation cross-linked acrylic based monomer systems. The validity of the method was tested on highly hydrophobic non-polar amorphous fluoro-polymers using a number of polar and low surface tension liquids. Contact angle hysteresis was present on these surfaces even though surface morphology of the solution processed fluoro-polymers is close to ideal. Estimated surface energies using such probe liquids were consistent varying slightly with the probe liquid type. On such highly ordered and non-polar polymer surfaces use of polar and low surface tension liquids results in accurate surface energy estimation. However, use of polar probe liquids commonly employed in surface energy estimation methods, such as, Harmonic mean (HM), Geometric mean (GM) or Lewis Acid-Base method (LWAB) on polar surfaces such as polyester resulted in inconsistent surface energy values. To strengthen this observation, the ASTM surface energy estimation procedure (ASTM D2578 04a) developed for polyethylene and polypropylene surfaces (both non-polar) was employed on a sample polar polyester surface using the ASTM probe liquids. Results showed inconsistent surface energy values supporting the conclusion that care must be exercised during use of polar probe liquids in estimating surface energy on polar polymers with the contact angle hysteresis method. Finally, UV radiation cross-linkable acrylic polymer surface energies were estimated with the hysteresis method. Surface energy results were consistent based on five different probe liquids. It was observed that surface energy of the cross-linked monomer networks decreased slightly with increasing UV curing time.

Commentary by Dr. Valentin Fuster
2006;():169. doi:10.1115/IMECE2006-16024.

In recent years shape memory effect in polymer systems has drawn great attention for its potential applications for MEMS and medical devices. In this paper, the visco-elastic and plastic behavior and strain recovery characteristics of a thermoplastic have been studied extensively. Creep deformation by compression was performed under load or displacement control mode, and under monotonic or cyclic loading. The strain recovery ratio of the shape memory polymer is found to be strongly affected by the deformation temperature, isothermal holding temperature and time, amount of forward strain and relaxation time, and the number of cycles of strain/recovery. The creep behavior of the material is modeled.

Commentary by Dr. Valentin Fuster
2006;():171-183. doi:10.1115/IMECE2006-13060.

A probabilistic micromechanics model had been developed for the unidirectional fiber-reinforced composite material design screening. In which, we used the predicted mechanical properties of IM-7 carbon fiber from the existing IM-7/5250-4 composite material system together with the observed 977-3 matrix mechanical properties to predict the probability density functions for the mechanical properties of IM-7/977-3 unidirectional composite. To include the material design in the structural design process, we had extended the probabilistic analysis to predict the probability density functions for the off-axis mechanical properties. The angle-ply and cross-ply laminates have been used extensively in aerospace structural designs. It is logical to extend the probabilistic analysis to predict the probability density functions for the mechanical properties of the laminated composite. We had provided the probabilistic analysis for a symmetric regular angle-ply laminate of IM-7/5250-4 composite laminate. In this report, we will focus on the probabilistic analysis of symmetric and anti-symmetric regular cross-ply laminates of IM-7/5250-4 fiber-reinforced composite with odd-number plies parallel to and even-number plies perpendicular to the laminate principal axes. These probabilistic micromechanics models provide a design-screening tool to help material producers to eliminate the unnecessary time-consuming and costly material fabrications and to reduce the numbers of testing to a minimum but enough to verify the model prediction. They also provide a structural analysis tool to help the structural designer to manage the structural and material uncertainties during the structural design process. And consequently, it provides a means to accelerate the insertion of materials into AF productions.

Commentary by Dr. Valentin Fuster
2006;():185-194. doi:10.1115/IMECE2006-13895.

This paper demonstrates ability to significantly increase buckling loads of perforated composite laminated plates by synergizing FEM and a genetic optimization algorithm (GA). Plate geometry is discretized into specially-developed 3D degenerated eight-node shell isoparametric layered composite elements. General shell theory, involving incremental nonlinear finite element equilibrium equation, is employed. Fiber orientation within individual plies of each element is controlled independently by the genetic algorithm. Eigen buckling analysis is performed using the subspace iteration method. Available results demonstrate the approach is superior to more conventional methodologies such as modifying ply thickness or the stacking sequence of individual rectilinear plies having common fiber orientation through the plate.

Commentary by Dr. Valentin Fuster
2006;():195-203. doi:10.1115/IMECE2006-14411.

To complement existing resin flow control strategies currently under development for Vacuum-Assisted Resin Transfer Molding (VARTM), and to provide the ability to react to unexpected changes in resin behavior during injection, a new technique for resin flow manipulation has been investigated. This approach consists of a semi-cylindrical shaped vacuum chamber placed on a mold which, when evacuated, increases the permeability of the region under the chamber by lifting the bag atop the mold. A finite element model has been developed to predict the resin flow within the mold while using the external chamber. Laboratory testing has shown significant modification in resin flow with reduced injection time. Using the external chamber, a robotic system has been prototyped that identifies dry regions forming during injection via computer vision, deploys the vacuum chamber over the mold with a robotic arm, and actuates the chamber in order to modify and correct the resin flow within the mold. Test results using lab-scale molds with large variations in preform permeabilities indicate that the robotic system can correct and/or modify the resin flow within a mold in real time, thus eliminating dry, unimpregnated regions. This computer-based method has the potential to significantly enhance molded part quality and consistency by eliminating resin starved regions within a molded composite part.

Commentary by Dr. Valentin Fuster
2006;():205-211. doi:10.1115/IMECE2006-15344.

In composites processing, the combination of thickness, mold temperature, and resin kinetics can lead to temperature overshoot within a part during cure. In this paper, the interplay between these variables was considered to establish a critical thickness separating parts having large overshoots from parts having small overshoots. The one-dimensional heat equation with an autocatalytic relation for curing was used to model the process. The equations were placed in dimensionless form using a scaling analysis. Five dimensionless groups were identified. Two of these groups were found to affect the overshoot of the temperature: the modified Damköhler number Da*, which distinguishes thin and thick composites and the dimensionless temperature ramp rate [Equation]trise , which depends on the boundary condition and heat transfer characteristics of the composite. To validate the scaling analysis, a finite difference model was created to calculate part temperatures during cure. The numerical analysis confirms that thin and thick parts, as defined by the relative temperature overshoot, can be predicted by Da* and [Equation]trise .

Commentary by Dr. Valentin Fuster
2006;():213-221. doi:10.1115/IMECE2006-13253.

The main objective of this study is to predict theoretically the stress distributions around the holes in a bolted joint made of particulate metal matrix composite and to investigate the associated load transfer efficiencies both for a single and double lap bolted joints. A three-dimensional finite element parametric model has been developed to examine the effects of various design parameters on the structural performance of such joints. The main feature of this model is explicit modeling of the sliding interfaces between the connected plates and the washers, and those between the hole and the bolt. The model response showed an excellent agreement with a closed form solution as well as experimental data. The results indicated that unsymmetric configuration of single lap joints causes bending as the load is applied, which is opposite of the double lap joints. This research quantifies the relationship between the stress developed around the hole and washer diameter, tightening pressure, and clearance between the bolt and hole. It was also observed that variations in Young's modulus have no significant effect on the stress concentration around the hole.

Commentary by Dr. Valentin Fuster
2006;():223-230. doi:10.1115/IMECE2006-13699.

Utilization of magnesium alloys within the field of vehicle design offers substantial opportunity for mass reduction. This has resulted in a wide range of automotive applications. More recently, the scope of application has been extended to include components that are considered crash critical. However, the magnesium die casting process is widely reported as producing parts that exhibit large local variation in part properties. Hence, this introduces the technical challenge of how to design effectively based upon these constraints. In order to better understand this phenomenon, two large size thin walled production components were examined. Tensile test coupons were extracted from multiple locations. Micro and macro level investigations were also conducted in an effort to identify the root cause of property variation. This paper discusses the influences of porosity on mechanical property variation, specifically tensile strain to failure. Further discussion is also presented, detailing a proposed empirical model, for the prediction of local strain to failure.

Commentary by Dr. Valentin Fuster
2006;():231-235. doi:10.1115/IMECE2006-13727.

An Environmental Protection Agency-funded project was the material flow analysis of naphthalene-containing products in an effort to eliminate, reduce, or replace the sources of naphthalene. The project analysis began with manufacturers who use naphthalene-containing products in their processes. It identifies the basic characteristics of naphthalene as a common polynuclear aromatic hydrocarbon, which is released to the environment. Included are likely sources of naphthalene emissions and releases as they were identified for further investigation. This paper, which is the sequel to IMECE 2005-82808, highlights a secondary objective of the project: to document the approach used in identifying the naphthalene flow from the raw material to its various products. This secondary objective was to show how process, product, and quantity data can best be gathered. Within the project, there were several means to collect data, some that have worked better than others. The purpose of this objective was to provide the framework of a proven approach to generating the material flow so that it can be followed for other priority chemicals that populate the EPA list.

Topics: Flow (Dynamics)
Commentary by Dr. Valentin Fuster
2006;():237-240. doi:10.1115/IMECE2006-14075.

A new procedure based on constructing orthonormal tensor basis using the form-invariant expressions which can easily be extended to any tensor of rank n. A new decomposition, which is not in literature, of the stress tensor is presented. An innovational general form and more explicit physical property of the symmetric fourth rank elastic tensors is presented. The new method allows to measure the stiffness and piezoelectricity in the elastic fiber reinforced composite and piezoelectric ceramic materials, respecively, using a proposed norm concept on the crystal scale. This method will allow to investigate the effects of fiber orientaion, number of plies, material properties of matrix and fibers, and degree of anisotropy on the stiffness of the structure. The results are compared with those available in the literature for semiconductor compounds, piezoelectric ceramics and fiber reinforced composite materials.

Commentary by Dr. Valentin Fuster
2006;():241-250. doi:10.1115/IMECE2006-14468.

This paper deals with a hybrid optimization of the degree of cure and temperature field into the work piece during the pultrusion manufacturing process. The procedure is based on the consecutive application of a heuristic technique (Genetic Algorithms), with an analytical method (simplex technique), to minimize an opportunely defined fitness function. The objective function measures the uniformity of the degree of cure, with a satisfactory mean value, in the exit cross section of the forming die, taking into account constraints related to the degradation of the processing resin system, due to an exothermic peak temperature major than the carbonisation temperature of the polymeric matrix. Optimal values of the temperatures of the die heating platens have been evaluated by applying the proposed procedure to a three dimensional thermo-chemical numerical model, solved using a finite difference scheme. The robustness of the developed optimization procedure has been tested using several combinations of process parameters, such as temperature of the resin bath, temperature of the die cooler, and composite material pull speed. A finite element model is used to analyze temperature field and degree of cure profiles after the optimization of the temperatures of the heating platens. The proposed procedure can be used as a good tool to optimize part quality or productivity, for the conventional pultrusion process, as well as, for post die shaping pultrusion, in which the processing part is completely formed out of the heating die and material cure is then completed using U.V. rays or other heating sources.

Commentary by Dr. Valentin Fuster
2006;():251-253. doi:10.1115/IMECE2006-14694.

In order to exhibit pharmacological activity at the bone cancer site, high-dose chemotherapy drugs need to be used. This often causes toxicity and unfavorable systemic adverse effects leading to significant problems to the patient. Since nanoparticles are in subcellular size, they can effectively entered to the cell membrane that could result in higher cellular uptake. In this study, we report preparation and characterization of poly(lactic-co-glycolic acid) - PLGA nanoparticles, which encapsulated with chemotherapy drug cisplatin.

Topics: Nanoparticles , Drugs
Commentary by Dr. Valentin Fuster
2006;():255-259. doi:10.1115/IMECE2006-14733.

In this paper a methodology is proposed to predict ductile damage in metal forming process by using a coupled thermomechanical finite element method. The simulation contains the influence of thermal effects on material properties. The interaction between the damage evolution and the temperature distribution caused by heat generation due large strains has been correctly described by the proposed model. The results obtained with simulation of sheet metal blanking process show the importance of the strong coupling between thermal effects, plasticity, and ductile damage effect at large plastic strain with contact/friction. This model can be used for the prediction of the temperature field in some dynamic metal forming or machining processes.

Commentary by Dr. Valentin Fuster
2006;():261-266. doi:10.1115/IMECE2006-15167.

To interpret the role of diffusion and reaction process, a cellular automaton model, which combines the surface growth and internal oxidation, was developed to explain the oxidation mechanism of stainless steels in high temperature corrosive liquid metal environment. In this model, three main processes, which include the corrosion of the substrate, the diffusion of iron species across the oxide layer and precipitation of iron on the oxide layer, are simulated. The diffusion process is simulated by random walk model. Mapping between present model and Wagner theory has been created. The gross features concerning the evolution of the involved process were founded.

Commentary by Dr. Valentin Fuster
2006;():267-276. doi:10.1115/IMECE2006-15784.

In this study, measurements form low-impact velocity experiments including embedded and surface mounted optical fiber Bragg grating (FBG) sensors were used to obtain detailed information pertaining to damage progression in two-dimensional laminate woven composites. The woven composites were subjected to multiple strikes at 2m/s until perforation occurred, and the impactor position and acceleration were monitored throughout each event. From these measurements, we obtained dissipated energies and contact forces. The FBG sensors were embedded and surface mounted at different critical locations near penetration-induced damaged regions. These FBG sensors were used to obtain initial residual strains and axial and transverse strains that correspond to matrix cracking and delamination. The transmission and reflection spectra were continuously monitored throughout the loading cycles. They were used, in combination with the peak contact forces, to delineate repeatable sensor responses corresponding to material failure. From the FBG spectra, fiber and matrix damage were separated by an analysis based on signal intensity and the behavior of individual Bragg peaks as a function of evolving and repeated impact loads. This provided independent feedback on the integrity of the Bragg gratings which can serve to eliminate errors in the strain data such as due to sensor debonding or fracture. The critical indicators present in the sensor spectra for the mapping of these sensor failure modes are derived.

Commentary by Dr. Valentin Fuster
2006;():277-284. doi:10.1115/IMECE2006-16001.

Numerous techniques for fabricating tissue engineering scaffolds have been proposed by researchers covering many disciplines. While literature regarding properties and efficacy of scaffolds having a single set of design parameters is abundant, characterization studies of scaffold structures encompassing a wide range of design parameters are limited. A Precision Extrusion Deposition (PED) system was developed for fabricating poly-ε-caprolactone (PCL) tissue scaffolds having interconnected pores suitable for cartilage regeneration. Scaffold structures fabricated with three-dimensional printing methods are periodic and are readily modeled using Computer Aided Design (CAD) software. Design parameters of periodic scaffold architectures were identified and incorporated into CAD models with design parameters over the practical processing range represented. Solid models were imported into a finite element model simulating compression loading. Model deformation results were used to identify apparent modulus of elasticity of the structure. PCL scaffold specimens with design parameters within the modeled range were fabricated and subjected to compression testing to physically characterize scaffold modulus. Results of physical testing and finite element models were compared to determine effectiveness of the method.

Commentary by Dr. Valentin Fuster
2006;():285-291. doi:10.1115/IMECE2006-15500.

The discovery of vapor grown carbon nanofibers has created a significant opportunity to develop high performance and cost-effective nanocomposite materials. However, significant challenges in the development of such composite materials lie in the poor dispersion of carbon nanofibers into polymer resins and the weak interfacial bonding between carbon nanofibers and polymer resins. These critical issues have to be addressed by chemical functionalization of carbon nanofibers. Understanding molecular interactions between functionalized carbon nanofibers and polymer resins is a crucial step towards their potential use in nanocomposites. In this work, the effects of surface functional groups on the molecular interactions between carbon nanofibers and polymer resins have been studied by using molecular dynamics simulations. It was found that chemical functionalization of vapor grown carbon nanofibers increased the amount of surface functional groups which disturbed the original smooth graphitic planes of carbon nanofibers. The functionalization of vapor grown carbon nanofibers decreased the amount of π-bonds on the nanofiber surface, which resulted in the weaker interaction with polymer resins. The simulation results provided fundamental information for the rational functionalization of vapor grown carbon nanofibers to manipulate their nanoscale properties in a predicative manner.

Commentary by Dr. Valentin Fuster
2006;():293-299. doi:10.1115/IMECE2006-13491.

The effect of solid particle erosion on the strength and fatigue properties of E-glass/epoxy composite was investigated. Solid particle erosion with SiC particles of 400 μm to 500 μm in diameter was simulated on 12 ply [45°/-45°/0°/45°/-45°/0°]s E-glass/epoxy composites with a constant particle velocity of 42.5 m/s and solid particle to air volume ratio of 6 kg/m3 at impact angles of 90°, 60°, and 30° for 30, 60, 90 and 120 seconds. Damaged and undamaged specimens were subjected to tensile tests while monitoring their acoustic emission (AE) activity. An erosion damage parameter was defined as a function of the particle impact angle and erosion duration to determine the residual tensile strength of the composite. Scanning electron microscope (SEM) images of the erosion damaged specimens revealed the same damage mechanism occurred at different impact angles. The AE stress delay parameter was used to predict the residual tensile strength of erosion damaged composites. Tension-tension fatigue tests were performed on virgin specimens and specimens exposed to erosion damage of 60 seconds and 90 seconds at 90° particle impact angle to observe the effects of erosion damage on the fatigue life. A modified Basquin's equation was defined to predict the fatigue life of the erosion damaged specimens.

Commentary by Dr. Valentin Fuster
2006;():301-307. doi:10.1115/IMECE2006-14551.

A series of experiments was recently performed to characterize the mechanical response of several different rigid polyurethane foams to large deformation. In these experiments, the effects of load path, loading rate, and temperature were investigated. Results from these experiments indicated that rigid polyurethane foams exhibit significant volumetric and deviatoric plasticity when they are compressed. Based on these experiments, a foam plasticity model that captures volumetric and deviatoric plasticity was developed. This model has a yield surface that is an ellipsoid about the hydrostat. These polymeric foams were also found to be very strain-rate and temperature dependent. Thus, a new viscoplastic foam model was developed to describe the mechanical response of these foams to large deformation at a variety of temperatures and strain rates. This paper includes a description of recent experiments and experimental findings. Next, development of a foam plasticity model and a viscoplastic foam model is described. Finite element simulations with the new models are compared with experimental results to show behavior that can and cannot be captured with these models.

Commentary by Dr. Valentin Fuster
2006;():309-316. doi:10.1115/IMECE2006-15154.

Composite materials are widely used in many engineering applications and are an attractive for armor design because of their increased high toughness, impact resistance, stiffness, and strength-to-weight ratios and the ability to tailor their designs to applications. In this paper, numerical simulation of impact on composites is being performed to predict ballistic limit velocities and evaluate the delamination behavior of different composite systems. The normal impact and penetration of blunt rigid projectile on laminated composite targets was developed to estimate the velocity for which the projectile has complete penetration, the ballistic limits and energy absorbed while perforating a given piece of armor. A non-linear, explicit, three dimensional finite element commercial code (ABAQUS) is used to simulate the response of armor targets at V50 impact velocities. The armor test panel is modeled as a multi-layered laminated plate with different composite systems, thickness, and stacking sequence. The three failure modes that represent the three stages of the penetration process namely transverse shear, tensile fiber breakage, and delamination are identified. The ballistic limit curves for different materials, thickness, and orientations are determined. The target interlaminar stress distributions along the thickness are graphically represented. Strain energy, Plastic dissipation and Kinetic dissipation energy curves for the whole model were obtained including thickness effects.

Commentary by Dr. Valentin Fuster
2006;():317-323. doi:10.1115/IMECE2006-15414.

Liquidmetal-1 (LM-1, Zr41.25 Ti13.75 Cu12.5 Ni10 Be22.5 ) is a bulk metallic glass that can be processed in large thicknesses (e.g. 10 mm) because of its low critical cooling rate (e.g. 1 K/s). Like other bulk metallic glasses, this material exhibits near theoretical strength and large elastic strains (~2%) under quasi-static loading conditions. In this work, the Split-Hopkinson Pressure Bar (SHPB) was employed to perform high strain-rate compression tests on annealed LM-1. An ultrahigh-speed camera was also employed to perform in-situ video of the deformation process of the experiments, and the macroscopic fracture behavior was examined after testing. In addition, a new insert design was developed to reduce the effects of stress concentrations on the specimen. SHPB testing, combined with in-situ video, was performed on as-cast LM-1 using this new experimental configuration to determine the failure modes. The results of these experiments are compared to previous results to understand better the effects of stress concentration on high strain-rate behavior of bulk metallic glass.

Commentary by Dr. Valentin Fuster
2006;():325-331. doi:10.1115/IMECE2006-15672.

Current aerospace and naval applications require blast and flammability resistance characteristics. Materials and formulations with flammability resistance properties are most suitable in these type applications since fire and smoke toxicity are inherently associated with blast situations. In this effort, VAHLUP fabricated epoxy nanocomposites are evaluated and characterized for flammability resistance properties such as effective heat of combustion, ignition time, rate of mass loss, rate of heat release and smoke density. The effects of nanoparticles on the mechanical properties of epoxy nanocomposites are also evaluated. Uncoated polyaramid papers (Kevlar, Nomex with heat release rates of 0.18, 0.175 MJ/m2 respectively) exhibit better flammability resistance properties than resin/nanocomposites coated polyaramid papers. VAHLUP fabricated epoxy nanocomposites exhibit better flammability resistance properties than cast epoxy nanocomposites. Kapton, polyimide film with ignition time of 90 seconds+] give the best overall flammability resistance properties. Mechanical properties of epoxy nanocomposites are enhanced by processing. The preliminary data of the influence of the post-curing protocol tend to suggest the 2.0% nanoclay level as the optimal clay content level with respect to mechanical properties.

Commentary by Dr. Valentin Fuster
2006;():333-338. doi:10.1115/IMECE2006-13670.

Because of its excellent catalytic activity and its ability to act as oxygen buffer causing simultaneous oxidation of hydrocarbons as well as the reduction of Nitrogen Oxide, Cerium Oxide (CeO2 ) is very special as a fuel additive for internal combustion engines. The present work investigates, through a series of experiments, the influence of the addition of CeO2 in the nanoparticle form on various physicochemical properties of Diesel oil, such as the cloud and pour points, the flash and fire points, the viscosity and the volatility which influence not only the spray characteristic but also the fuel atomization. Diesel oil samples, containing various percentage dosing levels of CeO2 nanoparticles of size range 20-30 nanometers are prepared using standard procedures of ultrasonic mixing, and used in the experiments. The physicochemical properties of the base fuel and the modified fuel are measured accurately using ASTM standard test methods. The effects on the individual fuel properties and the overall performance on a Diesel engine are studied, leading to inferences on the optimum dosing level.

Topics: Nanoparticles , Diesel
Commentary by Dr. Valentin Fuster
2006;():339-346. doi:10.1115/IMECE2006-14511.

A periodic structure is formed in a piezoelectric plate by intervallic polarizing oppositely along one direction. Wave propagation in this structure are studied with plane-wave expansion method. The polariton behavior in the plate is observed by solving Newton's equations of motion and Maxwell's equations simultaneously. Significant coupling between phonon and photon occurs in the vicinity of the center of the first Brillouin zone. By studying the band structure and field patterns, the resonance phenomenon can be explained. Adjusting the periodicity and thickness of the superlattice, the polariton behavior can exist in the frequency range of RF band. Since the polariton in the piezoelectric superlattice can be excited by electromagnetic waves, it can be applied to transducers and filters.

Commentary by Dr. Valentin Fuster
2006;():347-352. doi:10.1115/IMECE2006-15776.

Size effects on optical properties of self-assembled quantum dots are analyzed based on the theories of linear elasticity and of strain-dependent k-p with the aid of finite element analysis. The quantum dot is made of InGaAs with truncated pyramidal shape on GaAs substrate. The three-dimensional steady-state effective-mass Schrödinger equation is adopted to find confined energy levels as well as wave functions both for electrons and holes of the quantum-dot nanostructures. Strain-induced as well as piezoelectric effects are taken into account in the carrier confinement potential of Schrödinger equation. The optical transition energies of quantum dots, computed from confined energy levels for electrons and holes, are significantly different for several quantum dots with distinct sizes. It is found that for QDs with the the larger the volume of QD is, the smaller the values of the optical transition energy. Piezoelectric effect, on the other hand, splits the p-like degeneracy for the electron first excited state about 1~7 meV, and leads to anisotropy on the wave function.

Commentary by Dr. Valentin Fuster
2006;():353-357. doi:10.1115/IMECE2006-13703.

Since their development, shape memory polymers, urethanes, styrenes, and the like, have been of increasing interest in advanced material and structure design. The following is an experimental investigation into the effect polymer chain alignment has on the mechanical properties of a particular styrene shape memory polymer, Veriflex®. Aligning the polymer chains results in several material anisotropies; giving rise to the possibility of controllable, directional shape memory and modulus behavior and a basis for a multitude of prospective design concepts.

Commentary by Dr. Valentin Fuster
2006;():359-368. doi:10.1115/IMECE2006-13875.

Ceramic fuel cell, such as solid oxide fuel cell (SOFC), usually has three functional layers with one dense electrolyte in the middle and two porous electrodes on each side of it, which operates around 1000°C. Recent research activities in SOFC tend to lower the operation temperature to the range of 700°C-800°C due to improvement in mechanical properties, and reduction in costs. However, the state-of-the-art electrolyte yttria-stabilized zirconia (YSZ) under this reduced temperature produces relatively poor ionic conductivity. Ceria-based electrolyte is an excellent candidate in electrical properties under intermediate temperature range, even though it shows a lattice expansion by cerium reduction at the very low oxygen partial pressure occurring at the anode side. Hence, a bilayer yttria doped ceria (YDC) with thin YSZ protection at anode side is designed to maximize the ionic conductivity. However, this lattice expansion of cerium results in an internal stress under this SOFC consideration. In this paper, oxygen partial pressure dependent creep behavior of an edge crack at the bi-material interface (YSZ:YDC) is studied numerically. The steady state C* path independent integral is obtained from ABAQUS code. Bi-material and homogeneous cases are discussed under extensive creep. Finally, fracture analysis of an edge crack at the bilayer electrolyte is also investigated for homogeneous bilayer materials.

Commentary by Dr. Valentin Fuster
2006;():369-373. doi:10.1115/IMECE2006-14507.

In this work, we propose a new generation of sensors and actuators based on a piezoelectric polymer (PVDF) with embedded carbon nanotubes. Polyvinylidene fluoride (PVDF) double walled carbon-nanotubes (DWNT) composite films are prepared with the goal to develop new polymeric materials with enhanced electrical and electromechanical properties. Electrical conductivity and dielectric properties of polyvinylidene fluoride- double-walled carbon nanotubes composites are investigated as a function of frequency (10 Hz -1 MHz), and as a function of weight fraction (0.01-2 wt%). DWNT and PVDF are mixed under mechanical stirring and sonication. The dispersion is assessed by Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM), indicating a good dispersion. Differential Scanning Calorimetery (DSC) is used to study the effect of DWNTs inclusions on the glass transition temperature, Tg , and the crystallinity of the resulting PVDF composite. The percolation threshold is computed by using the bulk conductivity data and it is found that percolation occurs at about 0.19wt%.

Commentary by Dr. Valentin Fuster
2006;():375-381. doi:10.1115/IMECE2006-14508.

Sensors and sensing technologies to obtain flow information at near real time for the control of new underwater morphing structure applications are being investigated. Inspiration for a new type of fluid motion sensor finds its origin in the vibrissae (whiskers) of seals. Recent research has shown the remarkable sensitivity and specificity of these biological sensors to detect hydrodynamic trails left by potential prey. The impressive sensory performance characteristics of seal whiskers suggest the developmental potential for corresponding synthetic fluid motion sensors. An analytical study of the dynamic response of a synthetic whisker-like beam has been carried out to understand its response to predefined vortical flow fields. A parametric study has been conducted to examine how the geometrical and material parameters (i.e. length, cross-section, and stiffness) can be manipulated to produce characteristic responses for different applications. This theoretical understanding is being used in a companion experimental study to develop a synthetic whisker-like sensor. The performance characteristics of the experimental sensor are compared to the beam model predictions.

Commentary by Dr. Valentin Fuster
2006;():383-395. doi:10.1115/IMECE2006-15106.

This paper reviews various studies carried out on thermal issues in lithium-ion batteries. Although thermal behavior of Li-ion batteries plays an important role in performance, life cycle and safety of these batteries, it has not been studied as intensely as chemical characteristics of these batteries. In this review paper, studies concerning thermal issues on Li-ion batteries are classified based on their methodologies and the battery components being investigated. The methodologies include mathematical thermal modeling, calorimetry, electrochemical impedance spectroscopy and thermal management system method. The battery components that have been studied include anode, cathode, electrolyte and the whole cell.

Commentary by Dr. Valentin Fuster
2006;():397-404. doi:10.1115/IMECE2006-15187.

Ultra-high molecular weight polyethylene (UHMWPE) is a popular choice for the liner material of the acetabular cup and forms one of the articulating surfaces in total joint replacements (TJRs). Evaluating the tribological characteristics of UHMWPE on immediate contact with the physiological fluid is essential to understand pathways and mechanisms of eventual failure. In this study, the friction response and interfacial shear strength of a UHMWPE - ceramic interface was quantified using atomic force microscopy (AFM) before and after exposure to bovine serum albumin (BSA) solution. A 10% protein solution concentration was used to closely mimic protein levels in human physiological fluid. Medical grade UHMWPE samples with two different surface finishing treatments, milling and melting/reforming were used in the experiments. Friction response as a function of normal load was monitored on a particular area on each sample. Fluorescence microscopy was used to assess the protein adsorption on the test area. The interfacial shear strength of the interface was calculated from the friction data using contact mechanics. Contact angle measurements were also performed on the surfaces to evaluate the surface energies before and after protein adsorption. Correlations between the friction behavior and surface energy of the surfaces are discussed.

Commentary by Dr. Valentin Fuster
2006;():405-406. doi:10.1115/IMECE2006-15376.

Current protocols employed to measure wear of ultra-high molecular weight polyethylene (UHMWPE) utilize gravimetric and/or topographic measurement techniques. However, these methods may be subject to error due to creeping and fluid absorption capabilities of polyethylene. A novel process designed to avoid these errors was developed using Europium (Eu) as a tracer material to quantify polyethylene wear. Eu is a rare earth element that does not naturally occur in the human body and can be quantified using ICP-MS. By combining a solution of Eu – stearate with nascent UHMWPE powder, 9.5 mm diameter pins were molded and subjected to pin-on-disk testing. Samples of the testing lubricant were obtained at regulated intervals. These samples were analyzed for Eu quantification, which were then compared with the gravimetric pin measurements.

Topics: Wear , Europium
Commentary by Dr. Valentin Fuster
2006;():407-412. doi:10.1115/IMECE2006-15418.

Mechanical properties of fully yttria stabilized zirconia (F-YSZ) with different grain sizes were investigated using instrumented indentation. While the grain size effect on the yield strength was performed on both the coarse-grained and fine-grained F-YSZ, the grain boundary effect was studied on the coarse-grained F-YSZ by performing nanoindentation within the grains and on/near the grain boundaries. Little variations were observed on mechanical properties such as hardness and reduced modulus, interesting results were obtained on the grain boundary effect on the yielding load for the course-grained F-YSZ.

Commentary by Dr. Valentin Fuster
2006;():413-417. doi:10.1115/IMECE2006-15727.

Any dielectric material would vary its dielectric properties with deformation. By measuring these variations one could monitor stresses or strains with no mechanical interface with a load-bearing member. This effect, called dielectrostriction, can be formulated as a linear relation between the stress/strain and the dielectric response of a material. A planar capacitor on a rigid substrate is utilized to monitor the dielectrostriction effect. A rosette of such sensors can be located on the surface or embedded in the monitored part. A four-sensor rosette measures principal directions and difference of principal strains. Overall, this sensing technology shows a good potential for Non-Destructive Evaluation (NDE) and structural health monitoring of composite materials. This work provides theoretical background and experimental study of dielectrostriction response in polycarbonate, polyethylene, acrylic, and carbon nanotube composite materials.

Commentary by Dr. Valentin Fuster
2006;():419-426. doi:10.1115/IMECE2006-15957.

Aeroelastic tailoring requires structural compliance and thus often conflicts with stiffness requirements to carry prescribed aerodynamic loads. Recently, however, the application of cellular structural concepts has suggested the potential to achieve compliance while conserving required load-carrying capacity. Among the proposed concepts, a chiral geometry in particular is a novel configuration which features an in-plane negative Poisson's ratio which leads to a very high shear modulus, while maintaining some degree of compliance. In particular, the chiral geometry allows large continuous deformations of the airfoil assembly, with the constitutive material remaining in the linear region of its stress-strain curve. The ability to sustain large deformations without exceeding yield conditions is required to recover the original shape and to provide smooth deformations as required by aerodynamic considerations. In previous work, a coupled-physics model, comprising of simultaneous CFD and elastic analyses, is developed to investigate the influence of the chiral core geometry on the behavior of a given airfoil. The modification of geometric parameters defining the considered layout leads to significant variations in mechanical properties, which can be exploited to achieve various levels of compliance. The morphing capabilities of the proposed airfoil, quantified as camber changes, are evaluated for various design configurations of the internal core structure. Specifically, three such airfoils have been constructed to study the influence of core geometric parameters on the elastic behavior observed in numerical simulations. Experiments on the aforementioned airfoil samples are characterized by imposing large camber-wise deflections, via static loading, and measuring the resulting strain, both in the honeycomb core and in the airfoil profile. The experimental results confirm the ability of the airfoils to sustain large deflections while not exceeding yield strain limits, in addition to producing continuous deformations, which are critical for the implementation of aeroelastic tailoring.

Commentary by Dr. Valentin Fuster
2006;():427-431. doi:10.1115/IMECE2006-13053.

A polystyrene polymer has been reinforced with single wall carbon nanotubes (SWNTs) to effect multifunctional capabilities. The SWNTs are produced by the HipCo process and are subsequently dispersed in the polystyrene resin matrix. The dispersion of the SWNTs in the polystyrene is enhanced by the use of a surfactant and composite samples at 0.0%, 0.1%, 0.2% 0.3% and 1.0% SWNT by weight are made. A multifunctional material is defined as a material with at least one additional property other than mechanical properties, and the desire is that the mechanical properties are not deteriorated due to the added nano-constituents. In this study SWNT reinforced polystyrene nano-composites are evaluated for their electrical conductivity as a function of SWNT weight percentage. The reinforced polystyrene nanocomposites are then evaluated for static strength, ductility and fracture properties to determine the effect of the nano-constituents on these mechanical properties.

Commentary by Dr. Valentin Fuster
2006;():433-436. doi:10.1115/IMECE2006-13243.

Magnesium (Mg), which is the lightest structural metal known, is used in various high-end sectors due to its high specific strength and stiffness. In an attempt to further improve the mechanical properties of Mg, a judicious incorporation of reinforcements into Mg is recommended. Conventional micron-size particulate reinforced Mg composites are faced with the issues of low ultimate tensile strength and ductility due to particle cracking and particle matrix interfacial failures. To overcome these underlying problems and to look for further improvement in properties, the use of nano-size particles is investigated. Accordingly, Mg reinforced with 0.5, 1 and 2 volume percent of nanosize Y2 O3 respectively were synthesized using the disintegrated melt deposition technique. Mechanical property results reveal an improvement in yield and tensile strengths of the nanocomposites relative to pure Mg. Ductility of the nanocomposites remain relatively constant even with up to 2 volume percent of Y2 O3 particles added. The Mg nanocomposites synthesized exhibited excellent combination of properties that were more superior than conventional Mg-SiC composites.

Commentary by Dr. Valentin Fuster
2006;():437-442. doi:10.1115/IMECE2006-13254.

In the present study, effect of vapor grown carbon nanofiber on the mechanical and thermal properties of polypropylene was investigated. Firstly, nanofibers were dry-mixed with polypropylene powder and extruded into filaments by using a single screw extruder. Then the tensile tests were performed on the single filament at the strain rate range from 0.02/min to 2/min. Experiments results show that both neat and nano-phased polypropylene were strain rate strengthening material. The tensile modulus and yield strength both increased with increasing strain rate. Experimental results also show that infusing nanofiber into polypropylene can increase tensile modulus and yield strength, but decrease the failure strain. At the same time, thermal properties of neat and nano-phased polypropylene were characterized by TGA. TGA results have showed that the nanophased system is more thermally stable. At last, a nonlinear constitutive equation has been developed to describe strain rate sensitive behavior of neat and nano-phased polypropylene.

Topics: Carbon , Nanofibers
Commentary by Dr. Valentin Fuster
2006;():443-447. doi:10.1115/IMECE2006-13534.

In the present investigation, a high intensity ultrasonic liquid processor was used to obtain a homogeneous molecular mixture of epoxy resin and K-10 MMT clay. The clay were infused into the part A of SC-15 (Diglycidylether of Bisphenol A) through sonic cavitations and then mixed with part B of SC-15 (cycloaliphatic amine hardener) using a high speed mechanical agitator. The trapped air and reaction volatiles were removed from the mixture using high vacuum. Flexural tests were performed on unfilled, 1wt. %, 2wt. %, 3 wt. % and 4 wt.% clay filled SC-15 epoxy to identify the loading effect on mechanical properties of the composites. The flexural test results indicate that 2.0 wt% loading of clay in epoxy resin showed the highest improvement in strength as compared to the neat systems. After that, the nanophased matrix with 2 wt.% clay is then utilized in a Vacuum Assisted Resin Transfer Molding (VARTM) set up with satin weave carbon preforms to fabricate laminated composites. The resulting structural composites have been tested under flexural and tensile loads to evaluate mechanical properties. 13.5% improvement in flexural strength and 5.8% improvement in tensile strength were observed in carbon/epoxy nanocomposite. TGA and DMA tests were also conducted to observe the thermal stability of the structural composite.

Commentary by Dr. Valentin Fuster
2006;():449-455. doi:10.1115/IMECE2006-13811.

Dielectrostriction is variation of dielectric properties of material with deformation. Linear relation between stresses and dielectric response, called stress-dielectric rule, closely resembles stress-optical rule. In addition, microscopic model predicts that dielectrostriction measurements are very effective for studying microstructure and size distribution of the suspended inclusions. In this paper, dielectrostriction effect is probed in silicone/aluminum oxide (Al2 O3 ) suspensions having various distributions of micro- and nano-particles. A rosette of two planar capacitor sensors with mutually perpendicular electrodes is employed to detect the dielectrostriction responses and measure the strain-dielectric coefficients of suspensions during oscillatory shear flow. Experimental results confirm stress-dielectric rule for all suspensions; and show dielectrostriction response sensitive to particle distribution.

Commentary by Dr. Valentin Fuster
2006;():457-462. doi:10.1115/IMECE2006-14224.

Carbon nanotubes have received considerable attention because of their excellent mechanical properties. In this study, carbon nanotube - copper composites have been sintered by a mechanical mixing process. The interfacial bonding between nanotubes and the copper matrix was improved by coating nanotubes with nickel. Sintered pure copper samples were used as control materials. The displacement rate of nanotube-copper composites was found to increase at 200°C whereas that of nickel-coated nanotue-copper composites significantly decreased. The incorporation of carbon nanotubes and nickel-coated carbon nanotubes in the copper matrix decreased friction coefficients and increased the time up to the onset of scuffing compared with those of pure copper specimens.

Commentary by Dr. Valentin Fuster
2006;():463-469. doi:10.1115/IMECE2006-14466.

Carbon nanofibers (CNFs) and carbon nanotubes (CNTs) are considered as potential fillers for improving the mechanical, thermal, and electrical properties of polymer and polymer composites. One of the applications is to enhance the electrical conductivity of polymer by using CNFs as fillers. This kind of treatment will be useful in the situations where electrostatic dissipation capability of the polymer part is important. This paper presents an investigation of the electrical resistivities of CNF/polymer suspensions of different CNF concentrations, i.e., 2.0wt%, 3.0wt%, 4.5wt%, and 6.0wt%. For determining the electrical resistivities of the CNF/polymer suspensions, a DC-sensor was constructed and used in the experiments. The experimental results indicate that the electrical resistivity of the CNF-polyester suspension decreases as CNF weight fraction increases. In addition, the results show a dramatic decrease of the resistivity when the measurement time prolongs. An empirical model to predict the electrical resistivity evolution of the CNF/polyester suspension was proposed in this paper. Good agreement between the empirical model predictions and the experimental results was found.

Commentary by Dr. Valentin Fuster
2006;():471-477. doi:10.1115/IMECE2006-14591.

A shear piezoresistive effect has been observed for micrographite particles suspended in uncured silicone elastomer. A phenomenological formulation of piezoresistivity is presented and an experimental approach is discussed within this paper. The experimental objective is to extract two material parameters, fully describing the piezoresistance effect in deformed isotropic materials. A rheometer in the cone-and-plate configuration provides well-defined oscillatory shear flow of the suspension; it also measures rheological characteristics of the suspension. The piezoresistive response is probed using interdigitated electrodes, which are attached to the rheometer plate. The electrodes are arranged in parallel-to-flow and perpendicular-to-flow orientations. The signal acquired from two such orthogonal electrode pairs can be combined in a way to exclude any contribution of volumetric deformations to the piezoresistance signal. The experimental results indicate a second harmonic relationship between the mechanical oscillation and the resistive response. These two-probe measurement results represent the first observations of a non-volumetric deformation contribution to the piezoresistivity of viscoelastic liquid suspensions.

Commentary by Dr. Valentin Fuster
2006;():479-482. doi:10.1115/IMECE2006-14659.

A prototype microtome knife for cutting ~100 nm thick slices of frozen-hydrated biological samples has been constructed by use of multiwalled carbon nanotubes (MWCNT). A piezoelectric-based 3-D manipulator was used inside a scanning electron microscope (SEM) to select and position individual MWCNTs, which were subsequently welded in place by electron beam-induced deposition (EBID). The device employs a pair of tungsten needles with provision to adjust the distance between the needle tips, accommodating various lengths of MWCNTs. We have performed experiments to test the breaking strength of the MWCNT in the completed device with an atomic force microscope (AFM) tip. An increasing force was applied at the midpoint of the nanotube until failure, which was observed in situ in the SEM. The initial force/deflection data appear promising, and efforts are underway to characterize and improve the strength of the device by conducting more such tests and modifying the welding process.

Commentary by Dr. Valentin Fuster
2006;():483-489. doi:10.1115/IMECE2006-15098.

Our group at the Naval Research Laboratory is studying hierarchical arrangements of materials at multiple length scales and how such arrangements can be used to yield novel properties. We are investigating nanocomposites comprising a thermotropic liquid crystalline polymer (LCP) matrix reinforced with carbon nanofibers for potential structure + conduction multifunctional applications. The LCP matrix is known for its inherent hierarchical microstructure, and its fracture surface is typically characterized by fibrils ranging in size from nanometer to micrometer. The carbon nanofibers being compounded with the LCP matrix are vapor-grown carbon nanofibers (VGCF) and pre-processing techniques are being developed to eventually replace VGCF with single-wall carbon nanotubes (SWNT). Composites with VGCF content of 0, 1, 2, 5 and 10 wt.% were extruded using a twin-screw extruder to yield monofilaments in the range of 0.5 to 2 mm in diameter. The mechanical properties of extruded filaments were determined via quasi-static tensile tests and fracture surfaces examined under a scanning electron microscope. Porosity and hierarchical fibrillar structures were commonly observed in the fracture surfaces of tensile tested LCP and LCP-VGCF filaments. The LCP-VGCF filaments showed a maximum increase in strength and modulus of 20% and 35%, respectively, at 1-2 wt.% VGCF content. The dependence of mechanical properties on VGCF content was attributed to the interplay between the extrusion process parameters, VGCF dispersion and molecular alignment of LCP. In another set of experiments, LCP was thermo-mechanically pre-processed using a laboratory scale double-roll mixer and extruded using a Maxwell mixing extruder to yield monofilaments in the range of 0.2 to 0.7 mm. At 0.2 mm diameter, filaments of un-pre-processed and pre-processed neat LCP showed almost identical mechanical properties. At 0.7 mm diameter, however, pre-processed LCP filaments showed 10% and 30% degradation in strength and modulus, respectively, relative to un-pre-processed LCP. The lowered mechanical properties of pre-processed LCP were attributed to its chemical degradation during thermo-mechanical processing. Over the diameter range from 0.2 to 2 mm and irrespective of prior processing or extrusion method, the modulus and strength of neat LCP filaments increased with decreasing diameter. The strength and modulus dependence on filament diameter could be explained by the "skin-core" effect typically seen in liquid crystalline polymers. Future work will involve optimizing processing parameters for simultaneous enhancements in mechanical properties and electrical/thermal conductivity in LCP-VGCF/LCP-SWNT filaments.

Commentary by Dr. Valentin Fuster
2006;():491-496. doi:10.1115/IMECE2006-14109.

This paper reports some fracture characterization results of hydroxyapatite (HAP)-filled poly(ε-caprolactone) (PCL). For the fracture toughness tests, the HAP concentration was steadily increased. The effect of HAP phase in PCL on the fracture and tearing toughnesses was investigated. The techniques of essential work of fracture (EWF) and tear strength were attempted. T-peel test was also used to evaluate the adhesive bond strength between HAP and PCL components using compression molded PCL-HAP-PCL laminates. Little is reported on the interfacial adhesion properties between bioactive components in scaffold development. The influence of PCL layer thickness (1.25, 2.5 and 3.5 mm) on adhesive strength between HAP and PCL was investigated. The adhesion between HAP and PCL components was found to be relatively strong; however, the thickness of PCL layers did not significantly influence the adhesive strength.

Commentary by Dr. Valentin Fuster
2006;():497-506. doi:10.1115/IMECE2006-14585.

Poly (butylene terephthalate) (PBT) is an engineering thermoplastic polyester with excellent mechanical properties and a fast crystallization rate widely processed via extrusion and injection molding. Such processes require very complex deformation histories, which can influence the ultimate properties of the processed material and parts. For such systems, flow-induced structural changes in the material as a function of processing are of increasing interest in the field of polymer processing. Linear viscoelastic material functions, including the storage and loss moduli and magnitude of complex viscosity, are very sensitive to the structural changes occurring in the polymer melt. This initial study focuses on the shear-induced crystallization of PBT and PBT nanocomposites with multi-walled carbon nanotubes (MWNTs). (Shear-induced crystallization is a subset of the more general flow-induced crystallization behavior which is the long-term goal of this research.) The effects of shear history on the isothermal crystallization behavior of these materials were investigated. Time sweep experiments at constant frequency, temperature and strain amplitude were carried out employing small-amplitude oscillatory shear within a parallel-plate geometry. Samples obtained upon quiescent crystallization suggested that the rate of crystallization and crystallization temperatures were modestly affected by the presence and concentration of the nanotubes, consistent with the findings of the earlier reports. However, the characterized shear-induced crystallization behavior of the nanocomposites presented here indicate more significant changes in the crystallization temperature and the rate of crystallization occur as a result of the incorporation of the carbon nanotubes. The shear-induced crystallization behavior was affected by the deformation rate, temperature, and the concentration of the carbon nanotubes. These findings indicate that shear-induced crystallization of polymer nanocomposites (and in general flowinduced crystallization effects due to arbitrary flow fields in the melt state during processing) should be an integral part of attempts to generate a comprehensive understanding of the development of the microstructural distributions and the coupled ultimate properties of polymer nanocomposites.

Commentary by Dr. Valentin Fuster
2006;():507-510. doi:10.1115/IMECE2006-14859.

We present results on the mechanical properties of single freestanding poly-furfuryl alcohol (PFA) nanowires (aspect ratio > 50, diameters 100–300 nm) from experiments conducted using a MEMS-based uniaxial tensile testing device in-situ inside the SEM. The specimens tested were pyrolyzed PFA nanowires (pyrolyzed at 800° C).

Commentary by Dr. Valentin Fuster
2006;():511-517. doi:10.1115/IMECE2006-15268.

An approach of utilizing slowly crystallizing dynamics for fabrication of poly(lactic acid) (PLA) single-polymer composites (SPCs) was investigated. As a slowly crystallizing polymer, PLA can be prepared as two distinct physical forms, amorphous (or near-amorphous) PLA and highly crystalline PLA. In this study, near-amorphous PLA films and highly crystalline PLA fibers were combined to form a SPC using a rapid hot compaction method at a temperature about 40°C below PLA's melting temperature. It was found that, by rapidly heating an amorphous-crystalline lamination above PLA's glass transition temperature during manufacturing, amorphous films can be fused and good adhesion between the amorphous film and the crystalline fiber can be achieved. Mechanical testing showed that the tearing strength of the SPC is almost half an order higher that that of the original PLA film.

Commentary by Dr. Valentin Fuster
2006;():519-523. doi:10.1115/IMECE2006-15607.

With the rapid developments in polymer matrix nanocomposites, there is growing interest in understanding their behaviors under adverse service conditions. A simple literature search will show the tremendous number of publications on montmorillonite (MMT) filled nanocomposites. It is therefore natural to see that the degradation behaviors for MMT filled nanocomposites have also received a number of detailed studies [1–10]. It was observed that by introducing MMT particles into LDPE [5] and PP [6, 7] matrices, the rate of photo-oxidative degradation was much faster than the corresponding unfilled matrixes. Furthermore, the dispersion state of the MMT particles did not seem to have influence on the photo-degradation rate [5].

Topics: Nanocomposites
Commentary by Dr. Valentin Fuster
2006;():525-532. doi:10.1115/IMECE2006-16304.

Mechanical properties of nanocomposites consisting of epoxy substrate reinforced by randomly oriented graphite platelets are studied with Mori-Tanaka method in collaboration with molecular mechanics. Elastic constants of graphite nanoplatelets which are the inclusion phase of the micromechanical model are calculated based on their molecular force field. The calculated elastic constants are well compared with the both experimental data and other theoretical predictions in literatures. The results from Mori-Tanaka's method based on the graphite modulus calculation from molecular mechanics are found that nanocomposite moduli have strong dependence on the aspect ratios of reinforcing particles, but no direct size dependence. The predicted nanocomposite moduli compare favorably with modulus measurement of several graphite particles of various aspect ratios and sizes. The experimental data also shows that particle sizes have very weak effect on nanocomposite moduli.

Commentary by Dr. Valentin Fuster
2006;():533-540. doi:10.1115/IMECE2006-13290.

Freestanding vapor-deposited gold films 0.15 μm, 0.5 μm, and 1.0 μm thick were tested in tension with strain measured directly in the gage section by digital imaging. The average grain size of all three films was ~ 60 nm with some large grains in the 0.15 μm material. Young's modulus decreased as the thickness decreased - from 73.1 ± 6.7 GPa to 64.7 ± 9.9 GPa to 51.4 ± 10.6 GPa respectively. The yield stress decreased from 365 ± 25 MPa to 328 ± 28 MPa, but was 371 ± 36 MPa for the 0.15 μm film, which was more brittle. Microstructural studies provide no clear explanation for this behavior.

Commentary by Dr. Valentin Fuster
2006;():541-547. doi:10.1115/IMECE2006-14852.

The thermoelectric properties of aligned quantum dot chains are calculated taking in account the change in band structure due to quantum size effects. From the calculated band structure, the Seebeck coefficient and electrical conductivity are calculated in a constant relaxation time approximation (CRTA). The power factor is plotted as a function of the size and spacing of dots and an increase is shown in the power factor for decreasing dot size. The net power factor is calculated using a parallel conductor model. The results are compared to the case of randomly spaced dots which have a power factor calculated using an effective resistance model.

Commentary by Dr. Valentin Fuster
2006;():549-555. doi:10.1115/IMECE2006-14923.

This paper proposes a three dimensional electromigration model for void evolution in small scale interconnects. Concurrent kinetics of creep flow and surface diffusion as well as the effect of surrounding material are considered to provide better understanding of the evolution process. The multiple kinetics and energetics are incorporated into a diffusive interface model. A semi-implicit Fourier spectral method and the preconditioned biconjugate-gradient method are proposed in the computations to achieve high efficiency and numerical stability. We systematically studied kinetic processes from diffusion dominated to creep dominated. Which process dominates, as revealed by the analysis, is determined by a combination of viscosity, mobility, interconnect thickness, and void radius. Previous studies on electromigration suggest that the void shape evolution is determined by the competition between the electron wind force and the surface energy. There exists a critical initial void shape, which determines whether a void evolves into a slit or not. However, our simulations show that in the same situation a creep dominated process can lead to a quite different morphology. A spherical void can evolve into a bowl shape, and further split into two smaller voids. It is also shown that the interconnect geometry has an important effect.

Commentary by Dr. Valentin Fuster
2006;():557-564. doi:10.1115/IMECE2006-14926.

A brittle thin film bonded to a substrate is common in MEMS components. At the edge of the interface, high stress gradients exist. It has been observed that mechanical strengthening of the thin film with decreasing film size occurs due to two constraints, namely, the microstructural constraint and the geometrical constraint. Consideration of both these constraints is required to properly predict the size effect impact on the strength of a brittle thin film. In this paper, a statistical approach is developed to predict the size effect of a brittle thin film on a substrate.

Commentary by Dr. Valentin Fuster
2006;():565-570. doi:10.1115/IMECE2006-14294.

The properties of polymer blends are largely determined by their morphology. So it is significant to investigate the morphology development of polymer blends during processing. In this work the morphology development of polymer blend was studied during flow along a single screw extruder. The polymer blend used incorporated polypropylene (PP) as its matrix phase and a high-viscosity or low-viscosity polyamide-6 (PA6) as the disperse phase. The samples of blends were taken from different positions using specially designed sampling device along the extruder online during the processing and were then examined using scanning electron microscopy (SEM). The morphology of the dispersed phase was quantitatively analyzed using image analysis software. The morphology evolution of blends along the melt conveying zone of screw was simulated. Theoretically predicted morphology evolution is in reasonable agreement with the experimental results. The aim of this work is to provide a better insight in the morphology development of blend during processing.

Commentary by Dr. Valentin Fuster
2006;():571-582. doi:10.1115/IMECE2006-15814.

Tailoring the rheological properties of polymers is important for practical applications such as the stabilization of polymer emulsions, blends, and foams. Nanomaterial (i.e. Carbon Nanotubes, Carbon Nanofibers, Dendrimers, and Carbon Black) are an excellent way to modify the mechanical, thermal, electrical, and optical properties of materials. This paper presents steady shear and linear viscoelastic oscillation testing of three polymers: Polyethylene (PE); Polypropylene (PP); and Polystyrene (PS). These polymers were studied in bulk form and as composites containing designated volume fractions of nanomaterials over a range of processing temperatures and conditions. The nanomaterials investigated in this study include Carbon Black, Vapor Grown Carbon Nanofibers, Multiwalled Carbon Nanotubes, Single Walled Carbon Nanotubes, and COOH functionalized Single Walled Carbon Nanotubes. The nanocomposite samples used for rheological experimentation were manufactured by melt mixing and injection molding. We will address whether the melt rheological measurements can unequivocally detect the co-continuous composition range in such systems. We will also investigate the melt flow rate through nanomaterial concentration variations, as well as discuss the storage modulus (G'), viscous modulus (G"), and complex viscosity of homogeneous polymer materials versus carbon nanocomposite material at various frequencies.

Commentary by Dr. Valentin Fuster
2006;():583-587. doi:10.1115/IMECE2006-16072.

Stress and temperature response of Polyethylene (PE) nanocomposites is mapped and predicted using creep-recovery measurements. The results indicate that the PE nanocomposite exhibit nonlinear response. When montmorillonite layered silicates (MLS) are introduced into the polymer, the stress response deviates substantially. Recovery curves of the nanocomposites were lower than those of the creep response. Viscoplastic strain was lower in the case of the nanocomposites. The material responses are analyzed using mechanical analogs.

Commentary by Dr. Valentin Fuster

Nondestructive Evaluation

2006;():591-596. doi:10.1115/IMECE2006-13580.

Ti-6A1-4V alloy exhibits a very strong anisotropic texture caused by the existence of a preferred crystallographic orientation in the polycrystalline microstructure. This crystallographic alignment can result in anisotropic behavior of the material so that the material properties are different depending on whether they are measured in perpendicular or parallel direction. In addition to this morphological anisotropy, due to the dominantly hexagonal grain structure, the Ti-6A1-4V alloy also exhibited a substantial thermoelectric anisotropy. This study was conducted to investigate the effect of thermoelectric anisotropy on the thermoelectric power measurements in a highly textured Ti-6A1-4V specimen using a completely nondestructive technique based on the Seebeck effect. The result shows the thermoelectric power dependence associated with texturing and the macroscopic grain structure in a rolled Ti-6A1-4V specimen, which was annealed at 710°C for 2 hours and slowly cooled. The measurements clearly demonstrated that the intrinsic sensitivity of the thermoelectric contact technique is a very useful tool that could be exploited for quantitative nondestructive (QND) material characterization.

Commentary by Dr. Valentin Fuster
2006;():597-602. doi:10.1115/IMECE2006-13940.

Quality assurance monitoring and material characterization is of great importance in the pharmaceutical industry. If the tablet coating and/or core are defective, the desired dose delivery and bioavailability can be compromised. Tablet coatings serve a wide variety of purposes such as regulating controlled release of active ingredients in the body, contributing to the bioavailability of a particular drug or combination of drugs, during certain times and locations within the body, protecting the stomach from high concentrations of active ingredients, extending the shelf life by protecting the ingredients from degradation from moisture and oxygen, and improving the tablet's visual appeal. If a coating layer is non-uniform and/or contains surface or sub-surface defects, the desired dose delivery and bioavailability can be compromised. The Food and Drug Administration has initiated a program named the Process Analytical Technology (PAT) in order to ensure efficient quality monitoring at each stage of the manufacturing process by the integration of analytical systems into the procedure. Improving consistency and predictability of tablet action by improving quality and uniformity of tablets is required. An ideal technique for quality monitoring would be non-invasive, non-destructive, rapid, intrinsically safe and cost-effective. The objective of the current investigation was to develop, non-contact/non-destructive techniques for monitoring and evaluating drug tablets for mechanical defects such as coating layer irregularities, internal cracks and delamination using a laser-acoustic approach. In the proposed system, a pulsed laser is utilized to generate non-contact mechanical excitations and interferometric detection of transient vibrations of the drug tablets. Three novel methods to excite vibration in drug tablets are developed and employed: (i) a vibration plate excited by a pulsed-laser, (ii) pulsed laser-induced plasma expansion, and (iii) an air-coupled acoustic transducer. Nanometer-scale transient surface displacements of the drug tablets are measured using the laser interferometer. Signal processing techniques are then applied to these transient displacement responses to differentiate the defective tablets from the nominal ones. From the analysis of frequency spectra and the time-frequency spectrograms obtained under both mechanisms, it can be concluded that defective tablets can be effectively differentiated from the nominal ones.

Topics: Acoustics , Drugs
Commentary by Dr. Valentin Fuster
2006;():603-610. doi:10.1115/IMECE2006-14335.

Accurate calibration is required for high-precision mechanical stages used for inspection of mechanical parts. Because of the high cost involved in purchasing and maintaining Coordinate Measuring Machines (CMM), it is common that a dedicated or reconfigurable inspection machine is designed and built to give a solution for a specific inspection task. High precision stages and high precision sensors that are needed for this task can be purchased as off the shelf products. However, when precision is needed, the assembly of the sensor to a linear stage becomes a complex task. This task becomes even more complex when using a non-contact probe since them are more unknowns added to the problem. In this paper we give a method for calculating the angle between the probe beam and the motion stage. The calculation is done directly from the measurements obtained by the non calibrated system. Using the calculated angle, the inverse of the affine transform resulting from the lack of perpendicularity between the probe beam and the motion stage can be determined and can be fixed in software. The method utilizes a high precision cylinder for the task. By using the proposed method, the assembly of a non contact probe to a linear motion stage becomes as simple as bolting down the bolts on the sensor connection panel. The method has been verified by computer simulation, with and without random noise added to the measurements. The results are presented via graphs and tables at the end of this paper.

Topics: Sensors , Calibration
Commentary by Dr. Valentin Fuster
2006;():611-615. doi:10.1115/IMECE2006-16073.

Marine, aerospace, ground and civil structures can receive unexpected loading that may compromise integrity during their life span. Therefore, improvement in detecting damage can save revenue and lives depending upon the application. The prognostic capability is usually a function of the examiner's experience, background and data collection during the evaluation. Nondestructive evaluation (NDE) methods are varied and specific to a given type of system (material, damage type, loading and environmental scenarios). As a result, one method of damage detection alone cannot examine all possible conditions and may even give false readings. This work examined the transient thermal response technique to assess damage in a sandwich composite structure. The mathematical formulation of the problem is presented. Then, a numerical approximation technique is used to solve the governing equations. The thermal distribution on the surface of a beam model is analyzed when damage is introduced. Then, an experimental setup with an Infrared (IR) thermography camera was assembled in order to provide the necessary information about the surface temperature distribution over the beam. Several damages scenarios will be tested by the technique with the purpose of determining the limitations of the method. The obtained experimental data was used to validate the numerical model. Finally, the feasibility of this feature to use in damage detection is discussed.

Commentary by Dr. Valentin Fuster
2006;():617-627. doi:10.1115/IMECE2006-16131.

The spectral data i.e. eigenvalues (natural frequencies) and eigenvectors (mode-shapes), characterizes the dynamics of the system. Non-destructive vibration testing, involving advanced experimental modal analysis techniques, has a potential to obtain the spectral data of the structures. It is well known that the dynamic characteristics of a structure will change due to the change in its physical properties. In this research, such changes in spectral behavior will be exploited towards the detection of minuscule changes in the mass of microstructures such as cantilever micro-beams, micro-resonators and oscillators, by solving certain direct and inverse eigenvalue problems. Some piecewise uniform micro-cantilever beams are considered here and associated transcendental eigenvalue problems are developed. Examples relevant to the design and identification of such beams are demonstrated through systematic mathematical modeling and effective solution strategy. It is shown that spectral behavior of mass loaded piecewise uniform beams can be obtained accurately and efficiently. Moreover, location and severity of the loaded mass can be identified successfully by using finite number of eigenvalues which may be available from experiments. Such formulations can be useful for, design and optimization of microstructures (micro-cantilever beams, resonators etc.), Bio-MEMS sensor design for the detection of single/multiple microbiological cells, and structural health monitoring.

Commentary by Dr. Valentin Fuster
2006;():629-632. doi:10.1115/IMECE2006-16299.

In an effort to reduce deployment cost and time, the military is taking a closer look at how to more efficiently deploy and construct their shelters. In support of this effort, one current research topic is lightweight inflatable structures used for maintenance and shelter. While inflatable fabric structures are not new, recent developments have vastly improved the load-carrying capability and durability of these structures, allowing them to replace traditional framed tent structures. This is due in large part to the development of inflated structural members called airbeams, which are essentially pressurized fabric tubes with an impermeable internal bladder. The working pressures of the structural airbeams are upwards of 592 kPa. There are two major types of airbeams; woven and braided. The woven beams generally operate at lower pressures (69-296 kPa), while the more recently developed braided beams operate at much higher pressures (296-592 kPa). Since the technology of airbeams is relatively new, there are few standard material tests for determining the fabric constitutive properties necessary for airbeam design. This represents a significant barrier to their efficient implementation. This paper will present the current state of the art in relevant areas of textile testing and describe test practices useful for identifying the constitutive properties of the airbeam fabrics. In addition, preliminary testing of inflated airbeams will also be presented, and the results discussed.

Commentary by Dr. Valentin Fuster
2006;():633-638. doi:10.1115/IMECE2006-16306.

This paper presents a finite element analysis of inflated fabric beams that considers nonlinear material response and shear deformations. Applying the principle of virtual work, we obtain the FEM formulation for inflated fabric beams with material nonlinearity. Comparisons between 4-point bend tests of inflated woven fabric beams and finite element results indicate that the finite element analysis provides good estimates of deflections, and that it is important to incorporate the effects of shear deformation and pressure when predicting inflated fabric beam response.

Commentary by Dr. Valentin Fuster
2006;():639-648. doi:10.1115/IMECE2006-16307.

A swatch of plain-woven fabric was subjected to biaxial tests and its material characterization was performed. The stress-strain relations of the fabric were determined and directly used in finite element models of an air beam, assumed constructed with the same fabric, subjected to inflation and bending events. The structural responses to these events were obtained using the ABAQUS-Explicit[1] finite element solver for a range of pressures including those considered typical in safe operations of air inflated structures. The models accounted for the fluid-structure interactions between the air and the fabric. The air was treated as a compressible fluid in accordance with the Ideal Gas Law and was subjected to adiabatic constraints during bending. The fabric was represented with membrane elements and several constitutive cases including linear elasticity and hyperelasticity were studied. The bending behavior for each constitutive case is presented and discussions for their use and limitations follow.

Commentary by Dr. Valentin Fuster
2006;():649-651. doi:10.1115/IMECE2006-16309.

The underlying mechanics of airbeam structures continues to be a topic of current research. Airbeams are attractive because they have the advantage of outstanding strength-to-weight ratios, can deform without causing irreversible damage to the structure, and the deflated storage space is small. Major challenges in the analysis of airbeams include capturing fabric wrinkling under small compressive strains and incorporating the effects of internal pressure. This paper presents results from analyses of cylindrical woven airbeams using the commercial finite element software package ABAQUS. Models are created using a combination of shell and membrane elements, and loaded in three point bending. The models are solved as quasi-static using the ABAQUS/Explicit solver. The effects of mesh density and material damping on solution accuracy are investigated. Results of the finite element models are compared to experimental data.

Commentary by Dr. Valentin Fuster
2006;():653-659. doi:10.1115/IMECE2006-16360.

Airbeams, inflatable composite structures, have traditionally been used solely as structural elements. Modeling and test procedures have been under development by academia, industry and governmental agencies to predict and evaluate an airbeam's structural properties. However, the pneumatic component that gives airbeams their strength and stiffness also provides airbeams the capability to absorb energy. Test procedures and scaling laws that can be used to evaluate the energy absorbing capacity of these structural elements will be described and evaluated. Test data will show that airbeams can reliably absorb sufficient energy for applications such as a pneumatic fender and meet other functional requirements. The paper will also describe textile considerations and other material properties that will enable this application to be successful.

Commentary by Dr. Valentin Fuster
2006;():661-663. doi:10.1115/IMECE2006-13457.

Fatigue damage is the most common kind of failure for metal materials. Traditional non-destructive testing (NDT) methods fail to predict early fatigue damage. Magnetic Metal Memory (MMM) Testing, a new NDT technology, has the potential of fatigue damage evaluation. This paper aims to investigate fatigue mechanical property of ferromagnetic material with the MMM method. Steel Q235 samples with different depth and breadth artificial crack are tested in rotary bending fatigue machinery. The MMM fatigue features are as follows: the tangent component Hp(x) of magnetic induction intensity is gradually increasing up to the peak value while the fatigue crack is initiating and growing; after that peak, Hp(x) is descending with the crack deepening. Furthermore, the features have been studied theoretically.

Commentary by Dr. Valentin Fuster
2006;():665-674. doi:10.1115/IMECE2006-13533.

In structural health monitoring (SHM), a network of embedded sensors permanently bonded to the structure is used to monitor the presence and extent of damage. The sensors can actively interrogate the structure through ultrasonic waves. Among the ultrasonic waves, Lamb waves are quite convenient because they can propagate at large distances in plates and then interrogate a large area. Lamb waves in a plate can be produced with piezoelectric wafer active sensors (PWAS) that are small, inexpensive, unobtrusive transducers. PWAS can be surface-mounted on an existing structured or placed inside composite materials. PWAS sensors use the piezoelectric principle. An alternating voltage applied to the PWAS terminals produces an oscillatory expansion and contraction of the PWAS. An oscillatory expansion and contraction of the PWAS produces an alternating voltage at the PWAS terminals. PWAS are bonded to the structure through an adhesive layer; the coupling with the investigated structure is higher then conventional transducers. If the PWAS bonded to the structure is excited, it couples its in-plane motion with the Lamb wave particle motion on the material surfaces. In previous studies, the Lamb wave mode tuning between PWAS and isotropic plates has been observed experimentally and theoretically. Recently experiments have been performed to verify the presence of tuning between bonded PWAS and composite plates. In the present paper, it will be discussed a method, normal mode expansion (NME), for predicting the tuning frequencies of the PWAS-plate structure. This method can be used for both isotropic and non-isotropic material. Experimental values for the tuning frequencies in isotropic plates are compared with the theoretically data obtain with integral transform solution and NME.

Commentary by Dr. Valentin Fuster
2006;():675-684. doi:10.1115/IMECE2006-14387.

A self-sensing scheme, which allows using Lead Zirconate Titanate (PZT) materials for simultaneous sensing and actuation, has been developed in the context of structural health monitoring (SHM). Based on the self-sensing scheme developed, a time response of the PZT transducer coupled with a mechanical response of the host structure is successfully extracted while the same PZT transducer is excited by a specific input signal. Then, the measured PZT response is used for detecting transducer defects such as PZT cracking and debonding. In order to improve the reliability of transducer diagnosis, the reference-free transducer self-diagnosis scheme based on the developed self-sensing scheme is proposed. Finally, the effectiveness of the proposed self-diagnosis scheme is examined using PZT wafers instrumented on a fixed-free aluminum beam.

Commentary by Dr. Valentin Fuster
2006;():685-692. doi:10.1115/IMECE2006-15930.

This work describes a foundation of sophisticated diagnostic techniques for the detection of shaft cracks in rotordynamic systems, considering the dynamical behavior of a rotating cracked shaft under the application of external loads. The response is modeled as a modified Jeffcott rotor, while the crack is assumed to induce a time-varying stiffness in the model. The focus of this work is the development of external loading strategies to create damage sensitive measures of vibration response and then analyze that using advanced technologies such as wavelet analysis. This will enable the detection of the crack depth, as represented by the magnitude of the damage-induced time-varying stiffness, from vibration measurements. This entails developing external forcing functions for which features of the vibration response are sensitive to the presence of the damage. The development of such inputs is based on a multiple-scales analysis of the full equations of motion, including the time-varying stiffness. From this, a resonance (called combination resonance) is identified between the operating speed of the shaft, the fundamental frequency of the shaft, and the frequency of the external forcing. When the system is operated at this resonant condition, the translational vibrations of the shaft contain a spectral component near the fundamental shaft frequency that is proportional to the amplitude of the time-varying stiffness. The resonance bandwidth, obtained from this analysis, enables us to build a framework for the development of damage detection techniques for rotating machinery. Continuous Wavelet Transform (CWT) is applied to the vibration response of a rotordynamic system that utilizes harmonic forcing satisfying combination resonance. The variation of wavelet coefficients with respect to the variation of different system parameters is examined. Attention is focused on how the resonant bandwidth affects the variation of wavelet coefficients as crack grows.

Commentary by Dr. Valentin Fuster

Pressure Vessels and Piping

2006;():695-703. doi:10.1115/IMECE2006-13180.

The normalization method is adopted for standard specimens and extended for nonstandard specimens in this paper to develop J-R curves for X80 pipeline steel directly from load versus load-line displacement records without the need of crack length measurement. Standard deep cracked specimens usually contain high crack-tip constraint, while nonstandard shallow cracked specimens involve low crack-tip constraint. To examine constraint effect on fracture toughness, six single-edge notched bend (SENB) specimens with different crack lengths for an X80 pipeline steel are tested according to ASTM standard E1820-05. The normalization method is then used to determine the constraint dependent J-R curves for these SENB specimens. To validate the experimental results obtained from the normalization method, the conventional elastic unloading compliance method is also used to measure crack extension, and determine the J-R curves for the X80 steel. The results show that the J-R curves determined using the normalization method agree well with those based on the elastic unloading compliance method for all SENB specimens, except for those experiencing severe splitting. Therefore, the normalization method can be used to determine J-R curves for the X80 pipeline steel for standard as well as nonstandard specimens. In determining the J-integral values, the resistance curve procedure, the basic procedure and the modified basic procedure specified in ASTM E1820-05 are evaluated. Comparisons of the resulting J-R curves indicate that the modified basic procedure can be equivalent to the resistance curve procedure.

Topics: Steel , Pipelines
Commentary by Dr. Valentin Fuster
2006;():705-710. doi:10.1115/IMECE2006-13823.

Stress-assisted hydrogen diffusion analysis was performed on arc-shaped tension specimen (C-specimen) fabricated from Type 21-6-9 stainless steel. Two-dimensional finite element method was applied for the determination of elastic-plastic crack front stress fields, which was later coupled with hydrogen diffusion analyses. The extension of Fick's rule was used as the governing equation for the diffusion analysis. The distributions of hydrogen concentration were compared under various Internal Hydrogen Embrittlement (IHE) and Hydrogen Environment Embrittlement (HEE) conditions. Without any external hydrogen pressure in IHE conditions, the increment of hydrogen concentration driven by the gradient of hydrostatic stress was offset by the out-gasing driven by gradient of hydrogen concentration at the crack front region. As the hydrogen pressure increases, the hydrogen concentration at the crack front region becomes dominant and show peak value around the crack tip. Compared with the results of IHE cases, the hydrogen concentrations in HEE conditions could reach the level of steady state in a relatively short time which is attributed to the high solubility and diffusivity of the material at high temperature.

Commentary by Dr. Valentin Fuster
2006;():711-716. doi:10.1115/IMECE2006-14091.

Textile composites include woven, braided, and knitted fabrics. Textile composites are considered when out-of-plane properties are also important. Textile composites generally have better dimensional stability, out-of-plane properties, and impact and delamination resistance. The natural conformability of biaxial braids makes them more cost competitive than woven fabric. These material systems are gaining popularity, in particular for the small business jets, where FAA requires take off weights of 5670 kgf or less. The vacuum assisted resin transfer molding (VARTM) process has proven to be low in cost compared to resin transfer molding (RTM). Thus, the combination of biaxial braids and the VARTM process is likely to considerably reduce overall costs. Before the braids can be confidently used in the primary structures, it is necessary to understand the performance of biaxial braided composites under various loading conditions and especially under fatigue. This will reduce uncertainty and hence reduce the factor of safety in the design This research addresses viscoelastic effects on fatigue behavior of carbon/epoxy braided composites. It is observed that braided composites exhibit creep and stress relaxation. Further it is observed that frequency in axial fatigue loading plays dominant role in fatigue life, but very little role in fatigue failure mechanisms. Rate of stiffness degradation is greatly affected by frequency. These entire phenomena such as creep, stress relaxation, frequency effect, and dependency of stiffness on rate of loading indicate the viscoelastic behavior of braided composites. In this research different tests were performed to confirm viscoelastic behavior of braided composites. Axial tension-tension fatigue tests were conducted at different frequencies and stiffness degradation was studied.

Commentary by Dr. Valentin Fuster
2006;():717-726. doi:10.1115/IMECE2006-14329.

Miniature disk bending test was developed to evaluate the mechanical behavior of irradiated materials - mainly to identify the ductility loss in steels. The analytical solution for large amplitude, elasto-plastic deformation with contact and friction becomes rather unwieldy. It is difficult to distinguish between the regimes of elastic and plastic deformation since local plastic deformation occurs for very small values of load when the magnitude of spatial average stress is well below the yield stress. Thus the inverse problem of evaluating properties from the experimentally observed values of the deflection of the specimen is rather difficult to solve analytically. The paper discusses some of the published work in this area and the difficulties associated with them. The approach in this work is to first generate a large database - by a finite element (FE) solution - of load-displacement (P-w) records for varying material properties viz. elastic modulus (E), yield stress (σy ) and the constants (A0 , m) appearing in the plastic stress-strain relation. An artificial neural network (ANN) is trained with the specified material properties and the corresponding load-displacement records. In the second phase, this network is tested with known data and then used with the experimentally observed (P-w) records to predict the abovementioned material properties. The paper presents the details of modeling (FE and ANN), a summary of the results obtained by the FE analysis (database) and the results obtained by the ANNs in the training and the testing phases. The errors in the various values of the parameters during testing were found to be within 5%.

Commentary by Dr. Valentin Fuster
2006;():727-732. doi:10.1115/IMECE2006-15214.

Hydrogen environment embrittlement (HEE) of steels and alloys to be used in high-pressure hydrogen storage for fuel cell vehicles was investigated in 70 MPa hydrogen at room temperature. Candidate materials for high-pressure hydrogen storage, namely, stainless steels (i.e., SUS304; in the Japanese Industrial Standard (JIS), SUS316, SUS316L, SUS316LN, SUS310S, SUS630(17-4PH)), a low-alloy steel (SCM440), carbon steels (SUY, S15C, S35C, S55C and S80C), an iron-based superalloy (SUH660(A286)), Ni-based superalloys (Incoloy 800H, Inconel 718, Inconel 750, Hastelloy B2, Hastelloy C22), a copper-zinc alloy (C3771) and an aluminum alloy (A6061), were tested. SWP (piano wire), and SUS304, SUS316 and SUS631(17-7PH) wires used for springs were also tested. Tensile tests were conducted at room temperature using specially designed apparatus developed by our laboratory to measure the actual load on a specimen with an external load cell irrespective of the axial load caused by the high pressure and friction at sliding seals. In materials that contain Ni, i.e., stainless steels, and iron-based and Ni-based superalloys, HEE shows a variable Ni content dependence. We found that the effect of Ni equivalent on HEE of these materials shows a stronger dependence. HEE decreases with increasing Ni equivalent with grain boundary fracture or transgranular fracture along a martensite lath assisted by hydrogen for SUS630, SUS304, SUS316, SUS316LN and SUS316L. No HEE is observed in the given Ni equivalent range with dimple fracture for SUH660, SUS310S and Incoloy 800H; however, HEE increases with increasing Ni equivalent with transgranular fracture along a slip plane, that is along the interface between austenite and gamma', and with grain boundary fracture assisted by hydrogen for Inconel 718, Inconel 750, Hastelloy C22 and Hastelloy B2. These results and other HEE test results in high-pressure hydrogen obtained by AIST, i.e., results for 18 Ni maraging steel, low-alloy steels, high-Cr steels, Ni-based superalloys; are summarized in the AIST HEE data, which is compatible with NASA HEE data. HEE of the materials in high-pressure hydrogen is discussed. Internal reversible hydrogen embrittlement (IRHE) of some thermally hydrogen-charged austenitic stainless steels is also discussed in comparison with HEE of the steels.

Commentary by Dr. Valentin Fuster
2006;():733-740. doi:10.1115/IMECE2006-15612.

On the hand of the (mechanical) design of an existing, very large, extreme fixed tubesheet heat exchanger, a C2-Hydrogenation reactor in a petrochemical plant, various code solutions are compared, with each other and with a Finite Element solution based on the Direct Route in Design by Analysis (EN 13445-3, Annex B). The codes and standards used in the investigation are ASME Section VIII, Division 1 (and 2), (TEMA), and EN 13445-3, Clause 13 and Annex J. ASME VIII/2, and TEMA are not appropriate for this design. ASME VII/1 and EN 13445-3 Clause 13 approaches are similar. Differences in maximum permissible pressures result partly from different nominal design stresses. The modern EN 13445-3 Annex J approach, being based on limit analysis theory, leads to very different, much more efficient results. The Direct Route in Design by Analysis confirms the EN 13445-3 Annex J results, but gives, at the same time, clear insight into the behaviour of the whole structure and the various maximum permissible pressure limiting details.

Commentary by Dr. Valentin Fuster
2006;():741-750. doi:10.1115/IMECE2006-16325.

The technology of large scale hydrogen transmission from central production facilities to refueling stations and stationary power sites is at present undeveloped. Among the problems which confront the implementation of this technology is the deleterious effect of hydrogen on structural material properties, in particular at gas pressure of 1000 psi which is the desirable transmission pressure suggested by economic studies for efficient transport. To understand the mechanisms of hydrogen embrittlement our approach integrates mechanical property testing, TEM observations, and finite element modeling. In this work a hydrogen transport methodology for the calculation of hydrogen accumulation ahead of a crack tip in a pipeline steel is outlined. The approach accounts for stress-driven transient diffusion of hydrogen and trapping at microstructural defects whose density evolves dynamically with deformation. The results are analyzed to correlate the level of load in terms of the applied stress intensity factor with the time after which hydrogen transport takes place under steady state conditions. The transient and steady state hydrogen concentration profiles are used to assess the hydrogen effect on the mechanisms of fracture as they depend on material microstructure.

Commentary by Dr. Valentin Fuster

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