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Processing and Engineering Applications of Novel Materials

2009;():1-12. doi:10.1115/IMECE2009-10976.

Stress distributions in CFRP adhesive laminated plates subjected to static and impact out-of-plane loadings are analyzed using a three-dimensional finite-element method (FEM). For establishing an optimum design method of the laminated plates, the effects of some factors are examined. As the results, it is found that the maximum value of the von Mises equivalent stress σ eqv occurs at the edge of the CFRP’s interfaces. The maximum value of interface shear stress r i at CFRP interface decreases as the reinforced Young’s modulus and the thickness increases. However, the maximum value of σ eqv at the adhesive layer decreases as the reinforced Young’s modulus and the thickness decreases. In addition, the maximum value of r i at the CFRP’s interface of lower reinforced laminates under impact loadings shows opposite characteristics to those under static loadings. For verification of the FEM calculations, experiments were carried out to measure the strains at the interfaces and the laminates plates strengths. Concerning strain and strength prediction based on von Mises equivalent stress, fairly good agreements were found between the numerical and the experimental results. The FEM results of impacted strain are in fairly good consistent with the measured results. Discussion is made on the effects of some factors on interface stress distributions.

Commentary by Dr. Valentin Fuster
2009;():13-22. doi:10.1115/IMECE2009-11100.

Bolted joints inserting gaskets such as box-shape flange connections have been widely used in mechanical structures, nuclear and chemical industry, and so on. In automobile industry, box-shape connections are applied in oil-pan structure. They are usually used under internal pressure as well as other loadings such as thermal, impact loadings and so on. In designing the box-shape flange connections with gaskets, it is important to evaluate the sealing performance of connections under internal pressure. An important issue is how to evaluate the sealing performance in the connections by using the contact gasket stress distributions at the interfaces and how to determine the initial clamping bolt force (preload) for preventing leakage. In this paper, the stresses of box-shape flange connection with gaskets subjected to an internal pressure are analyzed using the finite element method (FEM), taking into account a hysteresis in the stress-strain curves of the gasket. The contact gasket stress distributions of the connections under the internal pressure are analyzed. The leakage tests were conducted using an actual box-shape flange connection with a gasket. Using the contact gasket stress distributions at the interfaces under an internal pressure (Helium gas was used) and the amount of the leakage measured in the experiment, the sealing performances are evaluated experimentally and numerically. Furthermore, the effect of the nominal bolt diameter, the bolt pitch and flange cover seating types (raised face / flat face) is examined on the sealing performances of box-shape flange connections. Discussion is made on the sealing performance in the above connections.

Commentary by Dr. Valentin Fuster
2009;():23-28. doi:10.1115/IMECE2009-13110.

This paper investigates the effect of storage time on the bond strength of plasma-activated silicon (Si) wafers. Plasma activation was carried out in a reactive ion etch chamber using O2 gas. The activated wafers were stored in a clean room environment for specific time intervals before pre-bonding them (in a high vacuum environment) using a substrate bonder. Steps involved in wet chemical activation and pre-bonding of the wafers were discussed in detail. The pre-bonded wafers were thermally annealed. The bond quality, in addition to the bond strength, of in-situ and ex-situ thermal annealed wafer pairs were evaluated. The bond quality was determined using near-infrared imagery, and tensile tests were conducted on dies diced out from the bonded pair. The chemistry involved during activation, storage, pre-bonding, and thermal annealing was investigated thoroughly. The bond quality and bond strengths of wafers for corresponding storage times were compared using the near-infrared imagery and tensile tests respectively. Finally interesting phenomenon, like the increase in bond strength after a particular storage time, was studied and explained.

Commentary by Dr. Valentin Fuster
2009;():29-35. doi:10.1115/IMECE2009-11000.

Electrospinning is a simple and versatile technique for producing micro- and nanofibers. It has been shown that electrospun tissue engineering scaffolds mimic the structure of the extracellular matrix of human body tissues. These scaffolds can improve cell attachment behavior and subsequent cell proliferation and differentiation. On the other hand, due to their large surface area to volume ratio and porous morphology, electrospun micro- and nanofibers are potentially useful for the controlled release of therapeutic agents (drugs and therapeutic biomolecules) in human bodies. In this study, electrospinning of poly(L-lactic acid) (PLLA) nonwoven micro- and nanofibrous membranes was investigated. It is known that the morphology and size of a drug carrier could play very important roles in the drug release behavior. Therefore, in the present investigation, a comprehensive study on the fabrication parameters that could affect the morphology and diameter of PLLA fibers was conducted. For electrospinning, several parameters were associated with intrinsic properties of the polymer solution, such as PLLA intrinsic viscosity, polymer solution concentration and solvent used, while other parameters were related to the experimental setup and electrospinning environment, including applied voltage, working distance, needle size, feeding rate, etc. Among these parameters, some solution related factors were important for controlling the fiber diameter. The average fiber diameter decreased from 3.2 μm to 0.6 μm when N,N-dimethylformamide (DMF) was added into a solvent system. While using dichloromethane (DCM) as the solvent, the fiber diameter could vary between 1 μm to 8 μm using different PLLA solution concentrations. Different solvent systems could also affect the morphology of PLLA fibers. On the other hand, most of the apparatus and environment related parameters could help to improve the fiber morphology, but not very significantly. It was also found that the stability of electrospinning conditions may improve the uniformity of PLLA fiber diameter. When lower voltage was applied, although the average fiber diameter increased, the range of variation of fiber diameters decreased. This study shows that PLLA fibrous membranes with a controllable average fiber diameter ranging from 600 nm to 8 μm could be fabricated via electrospinning. These fibrous membranes have the potential as vehicles for the controlled release of therapeutic agents in tissue engineering.

Commentary by Dr. Valentin Fuster
2009;():37-41. doi:10.1115/IMECE2009-11689.

Porous magnesium (Mg) alloys were processed by solid state sintering from mixture of elemental metal powders and pore-filling materials, such as, carbamide (urea). The porosity of the Mg alloy was controlled by selecting different particle size of the pore-filling and volume fraction material, as well as the sintering condition, which were arranged by a factorial experimental design. The effects of their porosity and porous structure were analyzed and the mechanical strength was evaluated with compression tests.

Commentary by Dr. Valentin Fuster
2009;():43-44. doi:10.1115/IMECE2009-11958.

Semiconductor and magnetic nanoparticles hold unique optical and magnetic properties, and great promise for bio-imaging and therapeutic applications. As part of their stable synthesis, the nanocrystal surfaces are usually capped by long chain organic moieties such as trioctylphosphine oxide. This capping serves two purposes: it saturates dangling bonds at the exposed crystalline lattice, and it prevents irreversible aggregation by stabilizing the colloid through entropic repulsion. These nanocrystals can be rendered water-soluble by either ligand exchange or overcoating, which hampers their widespread use in biological imaging and biomedical therapeutics. Here, we report a novel scheme of synthesizing fluorescent PbS and magnetic Fe3 O4 nanoparticles using DNA oligonucleotides. Our method of PbS synthesis includes addition of Na2 S to the mixture solution of DNA sequence and Pb acetate (at a fixed molar ratio of DNA/S2− /Pb2+ of 1:2:4) in a standard TAE buffer at room temperature in the open air. In the case of Fe3 O4 particle synthesis, ferric and ferrous chloride were mixed with DNA in DI water at a molar ratio of DNA/Fe2+ /Fe3+ = 1:4:8 and the particles were formed via reductive precipitation, induced by increasing pH to ∼11 with addition of ammonium hydroxide. These nanocrystals are highly stable and water-soluble immediately after the synthesis, due to DNA termination. We examined the surface chemistry between oligonucleotides and nanocrystals using FTIR spectroscopy, and found that the different chemical moieties of nucleobases passivate the particle surface. Strong coordination of primary amine and carbonyl groups provides the chemical and colloidal stabilities, leading to high particle yields (Figure 1). The resulting PbS nanocrystals have a distribution of 3–6 nm in diameter, while a broader size distribution is observed with Fe3 O4 nanoparticles as shown in Figure 1b and c, respectively. A similar observation was reported with the pH change-induced Fe3 O4 particles of a bimodal size distribution where superparamagnetic and ferrimagnetic magnetites co-exist. In spite of the differences, FTIR measurements suggest that the chemical nature of the oligonucleotide stabilization in this case is identical to the PbS system. As a particular application, we demonstrate that aptamer-capped PbS QD can detect a target protein based on selective charge transfer, since the oligonucleotide-templated synthesis can also serve the additional purpose of providing selective binding to a molecular target. Here, we use thrombin and a thrombin-binding aptamer as a model system. These QD have diameters of 3∼6 nm and fluoresce around 1050 nm. We find that a DNA aptamer can passivate near IR fluorescent PbS nanocrystals, rendering them water-soluble and stable against aggregation, and retain the secondary conformation needed to selectively bind to its target, thrombin, as shown in Figure 2. Importantly, we find that when the aptamer-functionalized nanoparticles binds to its target (only the target), there is a highly systematic and selective quenching of the PL, even in high concentrations of interfering proteins as shown in Figure 3a and b. Thrombin is detected within one minute with a detection limit of ∼1 nM. This PL quenching is attributed to charge transfer from functional groups on the protein to the nanocrystals. A charge transfer can suppress optical transition mechanisms as we observe a significant decrease in QD absorption with target addition (Figure 3c). Here, we rule out other possibilities including Forster resonance energy transfer (FRET) and particle aggregation, because thrombin absorb only in the UV, and we did not observe any significant change in the diffusion coefficient of the particles with the target analyte, respectively. The charge transfer-induced photobleaching of QD and carbon nanotubes was observed with amine groups, Ru-based complexes, and azobenzene compounds. This selective detection of an unlabeled protein is distinct from previously reported schemes utilizing electrochemistry, absorption, and FRET. In this scheme, the target detection by a unique, direct PL transduction is observed even in the presence of high background concentrations of interfering negatively or positively charged proteins. This mechanism is the first to selectively modulate the QD PL directly, enabling new types of label free assays and detection schemes. This direct optical transduction is possible due to oligonucleotidetemplated surface passivation and molecular recognition. This chemistry may lead to more nanoparticle-based optical and magnetic probes that can be activated in a highly chemoselective manner.

Topics: Nanocrystals , Proteins , DNA
Commentary by Dr. Valentin Fuster
2009;():45-53. doi:10.1115/IMECE2009-12574.

This study focused on chemical and physical properties of Hydroxyapatite powder was prepared by burning bone and heat treating the obtained bone ash at different temperatures (600, 700, 800, and 1100 °C) in an air furnace. The black ash was converted to a white powder after heat treatment. Results of X-ray diffraction analysis and Fourier transform infra-red spectroscopy that were done on heat treated powders in different temperatures indicated that the white powder was hydroxyapatite and did not contain any organic components of the bone. Furthermore, results of X-ray diffraction analysis were shown that phase transformation of the resulted hydroxyapatite to other calcium phosphate phases did not occur up to 1100 °C. X-ray fluorescence analyses revealed that calcium and phosphorous were the main elements and magnesium and sodium were present as minor impurities. The results of the energy dispersive X-ray analysis showed that Ca/P ratio of this natural hydroxyapatite varies between 1.46 and 2.01. The resulted material was found to be thermally stable up to 1100 °C. The density of natural hydroxyapatite heat treated at 800 °C was measured to be 3.187 g/cm3 .

Topics: Heat , Temperature , Bone
Commentary by Dr. Valentin Fuster
2009;():55-59. doi:10.1115/IMECE2009-12612.

In the present study, multilayer TiN/CrN coatings at different bilayer thicknesses have been deposited on silicon (100) and 316 stainless steel substrates using reactive DC magnetron sputtering technique. Nanoindentation, nanoscratch and ball-on-disk tribometer tests were used to characterize the films. Nanoindentation measurements showed enhancement in hardness values for all multilayer coatings with maximum hardness reaching 34 GPa which is about 45% improvement over the rule of mixtures. Nanoscratch tests revealed higher critical loads for multilayer coatings compared to monolayer TiN and CrN coatings. The tribometer tests showed better sliding wear performance for TiN/CrN superlattices.

Commentary by Dr. Valentin Fuster
2009;():61-66. doi:10.1115/IMECE2009-12627.

Solid Oxide Fuel Cell (SOFC) is a green energy technology that offers a cleaner and more efficient alternative to fossil fuels. The fabrication of miniaturized device structure for fuel cell manufacturing is a viable method for improving their efficiency. In this research, single chamber-SOFC with inter-digitized structure of electrolyte and electrodes has been developed by two novel methods. In the deposition method, the SC-SOFC design patterns were created with photolithography and micro-structured thin film electrolytes and electrodes were prepared with pulsed laser deposition (PLD). In the direct-writing method, micro-structured electrodes were injected on electrolyte substrates. These studies showed good potential of manufacturing methods for fabricating novel type of fuel cell design.

Commentary by Dr. Valentin Fuster
2009;():67-75. doi:10.1115/IMECE2009-12631.

Shape anisotropy of Nickel and Iron/Cobalt nanoparticles embedded respectively in gold and Titanium/Nitride thin film matrix on a sapphire substrate has been study. The samples have been fabricated using a pulsed laser deposition. The measurements of magnetic moment per cm2 versus magnetic field at different temperatures (10 K and from 50 K to 300 K every 50 K) and with a magnetic field applied parallel to the sample or perpendicularly have been made in order to determine the coercivity of the material for these parameters. We also report our investigation on the magnetoresistance effect per cm2 , where measurements have been lead for different temperatures (10 K, 100 K, 200 K, and 300 K) and two positions of the sample (parallel and perpendicular to the magnetic field). The comparison of the two cases, magnetic field parallel and magnetic field perpendicular to the sample, has shown that the difference of coercivity between them decreases when the temperature increases for all samples. For gold/nickel monolayer samples the difference varies from 120 Oe at 10 K to 6 Oe at 300 K for coercivities of about 200 Oe to 450 Oe at 10 K depending on the sample to coercivities of about 80 Oe to 150 Oe at 300K depending on the sample. For Titanium-Nitride/ Iron-Cobalt monolayer and trilayers samples the difference of coercivities varies between 10 Oe to 500 Oe depending on the temperature and the sample for coercivities between 30 Oe and 750 Oe. The difference in the percentage of magnetoresistance at 0 Oe is between 5 to 40% for Au/Ni sample and 0% to 10% for TiN/FeCo samples.

Commentary by Dr. Valentin Fuster
2009;():77-82. doi:10.1115/IMECE2009-12819.

This paper investigates the use of calcium alginate microcapsules to transport biomaterials for drug delivery. Rhodamine 6G dye was encapsulated in microcapsules for different formulations of the hydrogels using drop-on-demand printing. An experimental design was constructed to compare the effect of different concentrations of calcium chloride (M) and sodium alginate (% w/v) solutions in addition to the microcapsule diameter on the release kinetics profiles of the microcapsules. The results of these findings provide a basis to identify favorable sizes of microcapsules and concentrations of sodium alginate and calcium chloride solutions for controlled release behavior of microcapsules.

Topics: Drops , Printing
Commentary by Dr. Valentin Fuster
2009;():83-91. doi:10.1115/IMECE2009-12863.

Electrolytic plasma process is an efficient surface modification method for metallic materials. With proper control of the process parameters Electro-Plasma Process (EPP) could generate unique surface morphology, which is suitable for effective cleaning of the metallic surfaces and inherently, good adhesion strength can be achieved for eventual coating the surfaces. Increasing input voltage beyond the conventional Faraday region of electrolysis, luminous discharge is observed on the surface of one of the electrodes. The electrode surface must be covered by layers of bubbles before the discharge could be set in. The discharge of energy is then taken place in an explosive way with localized high temperature. The combination of heat and kinetic impact could effectively remove the surface contaminants and could produce a unique surface morphology. In this paper, the conditions of process control parameters and the resultant surface conditions that could be achieved are studied. It has been found that elevated temperature is beneficial towards the plasma formation on electrodes; and the increase of temperature essentially increases the kinetic energy of electrons in the electrolytic solution and a high electrolyte temperature assists the boiling process and the chemical reactions that generate bubbles. The conductivity of the electrolytic solution could also affect the threshold voltage and the current density, but the total power input does not vary significantly with conductivity. Environmental pressure has been proved to be the single most critical important factor for Electro Plasma Process; and by increasing the pressure level the total breakdown energy tends to increase and more importantly, the resultant surfaces manifest that the energy consumed for surface modification increases with pressure.

Commentary by Dr. Valentin Fuster
2009;():93-100. doi:10.1115/IMECE2009-13148.

This paper focuses on the effects of pressure and temperature in hot press molding on the mechanical properties of polypropylene-hydroxyapatite composites with two different types of silanated and unsilanated hydroxyapatite. Density, crystallinity, ultimate tensile strength, Young’s modulus and impact resistance were evaluated for the two types of composites. Increasing pressure caused enhancement of density, crystallinity, MFI, ultimate tensile strength and Young’s modulus. Increases in temperature increased MFI, ultimate tensile strength and Young’s modulus whilst decreased impact resistance of composites. Effects of increasing pressure and temperature on the mechanical properties of polypropylene-silanated hydroxyapatite were less than their effects on the mechanical properties of polypropylene-unsilanated hydroxyapatite. Micrographs showed changes in fracture mode from ductile to brittle with increasing pressure and temperature during hot press molding.

Commentary by Dr. Valentin Fuster
2009;():101-108. doi:10.1115/IMECE2009-12629.

This study aims at analyzing the shape change of red blood cells in the process of streaming through a capillary smaller than the red blood cell diameter. The characteristics of its shape change and velocity can potentially lead to an indicator of a variety of diseases. We approach this problem with considering red blood cells as surfactant covered droplets. This assumption is justified by the fact that the cell membrane liquefies under high pressure in small capillaries, and this allows the marginalization of the mechanical properties of the membrane. The red blood cell membrane is in fact a macro-colloid containing lipid surfactant. When liquefied, it can be treated as a droplet of immiscible hemoglobin covered with lipid surfactant in plasma surrounding. The merit is to analyze the effect of the flow condition and domain geometry on the surfactant concentration change over the droplet interface, and the effect of this change on the surface tension of the droplet. The distribution of the surfactant is calculated by enforcing conservation of the surfactant mass concentration on the interface, leading to a convection diffusion equation. The equation takes account of the effects of the normal and Marangoni stresses as a boundary condition on the interface between the immiscible fluids. The gradient in the surface tension adversely determines the droplet shape by effecting a local change in the capillary number, and influences its velocity by retarding the local surface velocity. The choice of the Gunstensen model is motivated by its capability of handling incompressible fluids, and the locality of the application of the surface tension. We used the same concept to investigate the dynamic shape change of the RBC while flowing through the microvasculature, and explore the physics of the Fahraeus, and the Fahraeus-Lindqvist effects.

Commentary by Dr. Valentin Fuster
2009;():109-116. doi:10.1115/IMECE2009-13101.

A biosensor is an electronic device that measures biologically important parameters. An example is a sensor that measures the chemicals and materials released during corrosion of a biodegradable magnesium implant that impact surrounding cells, tissues and organs. A responsive biosensor is a biosensor that responds to its own measurements. An example is a sensor that measures the corrosion of an implant and automatically adjusts (slows down or speeds up) the corrosion rate. The University of Cincinnati, the University of Pittsburgh, North Carolina A&T State University, and the Hannover Medical Institute are collaborators in an NSF Engineering Research Center (ERC) for Revolutionizing Metallic Biomaterials (RBM). The center will use responsive sensors in experimental test beds to develop biodegradable magnesium implants. Our goal is to develop biodegradable implants that combine novel bioengineered materials based on magnesium alloys, miniature sensor devices that monitor and control the corrosion, and coatings that slow corrosion and release biological factors and drugs that will promote healing in surrounding tissues. Responsive biosensors will monitor what is happening at the interface between the implant and tissue to ensure that the implant is effective, biosafe, and provides appropriate strength while degrading. Corrosion behavior is a critical factor in the design of the implant. The corrosion behavior of implants will be studied using biosensors and through mathematical modeling. Design guidelines will be developed to predict the degradation rate of implants, and to predict and further study toxicity arising from corrosion products (i.e., Mg ion concentrations, pH levels, and hydrogen gas evolution). Knowing the corrosion rate will allow estimations to be made of implant strength and toxicity risk throughout the degradation process.

Commentary by Dr. Valentin Fuster
2009;():117-126. doi:10.1115/IMECE2009-10488.

Hot embossing is a compression molding technique used for high replication accuracy of small features. One of the most sensitive phases of the process is the de-embossing stage during which the patterned part has to be demolded. In this paper, the demolding stage is considered as a frictional contact problem between a rigid mold insert and a viscoelastic polymer sheet as it deforms and cools inside a mold under an applied force. The contact is modeled with a modified Coulomb’s law of dry friction while a generalized Maxwell model is used to describe the polymer behavior during embossing, cooling and de-embossing stages. The heat transfer between the mold insert and the patterned polymer sheet is solved through a domain decomposition method. A finite element approximation based on a penalized technique is proposed and analyzed. The purpose of this modeling approach is to predict dimensional stability and residual shape of microcomponents in the hot embossing process. Such a prediction will allow one to assign appropriate processing conditions that minimize geometrical imperfections and increase replication accuracy.

Commentary by Dr. Valentin Fuster
2009;():127-134. doi:10.1115/IMECE2009-10635.

In this study the effect of moderate magnetic fields on the microstructure of a structural epoxy system was investigated. The changes in the microstructure have been investigated quantitatively using wide angle x-ray diffraction (WAXD) and pole figure analysis. The mechanical properties (modulus, hardness) of the epoxy were probed using nanoindentation. Using the continuous complex compliance analysis, the effect of the low magnetic fields on the viscoelastic properties of the epoxy was investigated. The phase lag angle was measured for both neat and magnetically annealed polymer. The results of this investigation reveal that under low magnetic fields both the quasi-static mechanical properties together with the viscoelastic behavior of the epoxy have been improved.

Commentary by Dr. Valentin Fuster
2009;():135-142. doi:10.1115/IMECE2009-11307.

This study aims to show the implementation of an optimization procedure by characterizing the material’s hyperelastic behavior in harsh environments experienced in facility testing and in real world automotive conditions. The procedure consists of conducting material tests under various simulated harsh environments, determining the co-efficients for hyperelastic material modeling and using FEA to predict and correlate the nature of failure observed in facility testing. Two commercially available and commonly employed thermoplastic elastomers (TPE), Santoprene (Ethylene-Propylene-Diene-Monomer rubber and Polypropylene blend) and Desmopan (Thermoplastic Polyurethane), were tested. The harsh environments simulated are fluid immersion tests in automobile grease. Material aging characteristics in controlled thermal conditions were also documented. Compression and tension tests were conducted in order to determine the co-oefficients of the Mooney Rivlin hyperelastic material model. Finite Element Analysis (FEA) simulations were conducted on LS-DYNA software, to determine the quasi-static stress distributions on an overslam bumper part, a typical application of automotive elastomers. Shape and topological variations were investigated in the FEA tests. It was found that certain shape and topological changes to the part result in minimizing the stress concentrations. It is hypothesized that such changes to the rubber component would result in a lower failure rate in facility testing.

Commentary by Dr. Valentin Fuster
2009;():143-145. doi:10.1115/IMECE2009-11470.

To electrically activate the shape recovery in a styrene-based shape-memory polymer (SMP) by coating with conductive carbon nanofiber paper has been demonstrated in this paper. Carbon nanofibers in the form of paper sheet in combination with SMP significantly improve the electrical and thermal conductivity of polymer, leading to the actuation of SMP/nanopaper composite (with 15% volume fraction of carbon nanopaper, dimension of 10.0 cm × 0.5 cm × 0.3 cm) can be carried out by applying 8.4 V voltage, with response time of 140 s. Therefore, electrical conductivity of 6.6 S/cm is obtained. This approach, although demonstrated in styrene-based polymer, is applicable to other type of SMP materials. Furthermore, the morphologies of carbon nanofiber in the form of paper is observed by scanning electron microscopy, and the thermomechanical properties of composites are measured and analyzed by dynamic mechanical analysis.

Topics: Carbon , Polymers , Shapes , Heating
Commentary by Dr. Valentin Fuster
2009;():147-155. doi:10.1115/IMECE2009-11544.

Polymeric optical fibers are generally manufactured in the same manner as traditional glass (silica) fibers. As technology advances, more efficient, cost effective materials and processes are being developed to serve the duties of optical materials within networks. Traditional polymer optical fibers are comprised of hydrocarbon amorphous polymers and include polymethyl methacrylate (PMMA) and polystyrene (PS). These types of polymers have inherent issues in optical applications such as their signal absorption loss. This is largely due to the vibration of the carbon-hydrogen (C-H) bond contained in the polymer backbone. Therefore, to broaden the scope of polymer optical fibers, novel exotic amorphous polymers are being developed. One such polymer family, reported to have excellent optical properties, is perfluorocyclobutyl aryl ethers (PFCB), which do not exhibit the strong C-H vibrations associated with absorption loss. At this time, little is known of the intrinsic properties of PFCBs as well as the behavior of the polymer melt during extrusion. This work will review the thermal and rheological properties of two PFCB polymers: biphenylvinyl ether (BPVE) and hexafluoroisopropylidene vinyl ether (6F). The information gathered from the analysis of these two intrinsic properties will be used as the input data for a fiber extrusion simulation model, FiSim. The application of the FiSim software was done in order to produce a viable limited range of process conditions for which fibers could be melt spun.

Commentary by Dr. Valentin Fuster
2009;():157-160. doi:10.1115/IMECE2009-12801.

This paper describes the design and development of device capable of measuring the force output of ionic polymer-metal composites (IPMC) actuators in two dimensions. Results from an experiment on a rectangular IPMC (17 mm × 7 mm × .07 mm) are used to show that blocked force output across the actuator varies by greater than 85% for a 3V input (Fig. 1). This decrease in blocked force output is shown to be exponential and occurring along the length. Deviations in single digit mN force output for the actuator are shown to generally be less than 10%.

Topics: Force
Commentary by Dr. Valentin Fuster
2009;():161-167. doi:10.1115/IMECE2009-13086.

A reduction in mechanical properties has been observed in Friction-Stir-Welded (FSW) Aluminum panels. This reduction in strength has generally been attributed to Residual Oxide Defect (ROD). From NASA experience it was also found that certain processing parameters would yield these reduced mechanical properties. The strength of FSW Aluminum panels generally decreases with increasing tool travel rate, decreasing rotation speed, and offset of the weld seam to the retreating side of the FSW tool. The microstructure of welds exhibiting these strength reduction as well as welds that behaved as expected were examined to determine microstructural effects of processing parameters. Therefore the evolutions of microstructural properties are immensely important to understand and evaluate to avoid any catastrophic failures due to the defects arising from welding operations. Scanning Electron Microscopy shows that these weld conditions are accompanied by large precipitates along the grain boundary for both AA-2219 and AA-2195 FSW welded samples. Transmission Electron Microscopy (TEM) also shows the precipitates to be “theta particles (Al2 Cu)” and intermetallics in the AA-2219; and T1 (Al2 CuLi), and TB particles in the AA-2195. The large size and heavy distributions of these precipitates, especially on the advancing side of the weld seam may influence these properties. It is determined that the existence of ROD in the samples must be analyzed systematically and carefully through the evolutions of microstructures, if catastrophic failures are to be avoided during service conditions. A more complete understanding of this phenomenon is necessary to ensure consistent and predictable weld properties thereby reducing or eliminating the risk of unforeseen failures.

Commentary by Dr. Valentin Fuster
2009;():169-175. doi:10.1115/IMECE2009-13174.

Four processing parameters, including compression force, compression time, compression distance, and delay time, were investigated in terms of their effects on the fiber orientation in injection-compression molded (ICM) short-fiber-reinforced polypropylene parts. The results reveal that the fiber orientation pattern in ICM parts is different from that in conventional injection molded parts. Compression force plays an important role in determining the fiber orientation, whereas the effect of compression time can be neglected. Moreover, the fiber orientation changes obviously in the width direction, with most fibers arranging orderly in the flow direction at positions near the mold cavity wall.

Topics: Fibers , Compression
Commentary by Dr. Valentin Fuster
2009;():177-182. doi:10.1115/IMECE2009-10084.

Due to elevated temperatures, excessive stresses and severed corrosion conditions, turbine engine components are subject to creep processes that limit the components life such as a turbine bucket. The failure mechanism of a turbine bucket is related primarily to creep and corrosion and secondarily to thermal fatigue. As a result, it is desirable to assess the current condition of such turbine component. This study uses the eddy current (EC) nondestructive evaluation technique in an effort to monitor the creep damage in a nickel base super-alloy, 7FA stage 2 turbine bucket after service. The experimental results show significative electrical conductivity variations in eddy current images on the creep damage zone of nickel base super-alloy samples cut from a turbine bucket. Thermoelectric power (TEP) measurements were also conducted in order to obtain a direct correlation between the presence of material changes due to creep damage and the electrical conductivity measurements.

Commentary by Dr. Valentin Fuster
2009;():183-187. doi:10.1115/IMECE2009-10697.

Infrared thermographic technique was employed for evaluating the temperature response in a Stainless steel grade 304 material subjected to different loading conditions such as monotonic tensile and compressive loading. In-situ temperature measurements were made from surface of the material by an infrared thermographic camera (JADE LWIR, Cedip Infrared Systems) while the material is being loaded. Cylindrical low cycle fatigue (LCF) samples were used in this study for monotonic tensile loading. Similarly, samples of aspect ratio 1.5 were used for analyzing monotonic compressive loading. As a material is subjected to tensile elastic loading, it undergoes cooling and when subjected to compressive loading, it undergoes heating. This phenomenon is called thermo-elastic effect. Based on our experimental observations, in case of monotonic tensile loading, the temperature of the material decreases till the material yields due to thermo-elastic effect and increases as the material plastically deforms, due to conversion of mechanical work done on the specimen into heat. But for the case of compressive loading, the temperature increases when the material is stressed in both cases of elastic as well as the elasto-plastic segment. This paper discusses the slope of the temperature response with respect to strain induced in the material and the effect of loading rate on the temperature measurements for the monotonic tensile and compressive loading. Comparison between the thermo-elastic slopes revealed that the thermo-elastic slope for the tensile loading is steeper than the slope from the compressive loading due to surface area contraction during the tensile loading and vice-versa. Experiments conducted at various loading rates ranging from 0.75 to 10 mm/min reveals that as the loading rate increases, temperature of the material increases.

Commentary by Dr. Valentin Fuster
2009;():189-198. doi:10.1115/IMECE2009-10802.

The fatigue crack propagation behavior of magnesium single crystal was analyzed using molecular dynamics simulation. The inter-atomic potential used in this investigation is Embedded Atom Method (EAM) potentials. The studies of the influences of crystal orientation and strain rate were perfomred using CC (center crack) and EC (edge crack) specimen. For CC specimen, the periodic boundary conditions were assigned in the x and z direction, while for EC specimen, only z direction was allowed periodic boundary conditions. In order to study the orientation dependence of fatigue crack growth mechanism, ten crystal orientations of initial crack, namely, orientation A-(12̄10) [101̄0], orientation B-(101̄0)[12̄10], orientation C-(101̄0)[0001], orientation D-(12̄10)[0001], orientation E-(0001)[101̄0], orientation F-(0001)[12̄10], orientation G (101̄1)[1̄012], orientation H (101̄1)[12̄10], orientation I (101̄2)[101̄1], and orientaton J (101̄2)[12̄10] were analyzed and the simulation results reveal that the fatigue crack growth rate and the crack path vary significantly with the crystallographic orientations of initial crack. The growth rate of orientaton G is the highest and the resistance of fatigue crack growth of orientation B is the highest. A CC specimen was employed to demonstrate the fatigue damage caused by pyramidal slip band under increased maximum strain cyclic loading in the specimen of orientation E. The analysis of the influences of strain rate was carried out on the orientation C, D, F, and G and the results revealed that the growth rate of fatigue crack decreasing with increasig strain rate. Fatigue growth rate can be expressed by da/dN = cΔCTOD, where the constant c was determined by the present atomistic simulations. The values of the constant c are large and vary widely from on orientation to another.

Commentary by Dr. Valentin Fuster
2009;():199-208. doi:10.1115/IMECE2009-12896.

Friction-Stir-Welding (FSW) has been adopted as a major process for welding Aluminum aerospace structures. AA-2195 is one of the new generations Aluminum alloy (Al-Li) that has been used on the new super lightweight external tank of the space shuttle. The Lockheed Martin Space Systems (LMSS), Michaud Operations in New Orleans is continuously pursuing FSW technologies in its efforts to advance fabrication of the external tanks of the space shuttle. The future launch vehicles which will have to be reusable, mandates the structure to have good fatigue properties, which prompts an investigation into the fatigue behavior of the friction-stir-welded aerospace structures. The butt-joint specimens of Al-2195 are fatigue tested according to ASTM-E647. The effect of Stress ratios, Corrosion-Preventive-Compound (CPC), and periodic Overloading on fatigue life is investigated. Scanning Electron Microscopy (SEM) is used to examine the failure surfaces and examine the different modes of crack propagation i.e. tensile, shear, and brittle modes. It is found that fatigue life increases with the increase in stress ratio, the fatigue life increases from 30–38% with the use of CPC, the fatigue life increases 8–12 times with periodic overloading; crack closure phenomenon dominates the fatigue facture. Numerical Analysis using FEA has also been used to model fatigue life prediction scheme for these structures, the interface element technique with critical bonding strength criterion for formation of the new surfaces has been used to model crack propagation. The fatigue life predictions made using this method are within the acceptable ranges of 10–20% of the experimental fatigue life. This method overcomes the limitation of the traditional node-release scheme and closely follows the physics of crack propagation.

Commentary by Dr. Valentin Fuster
2009;():209-216. doi:10.1115/IMECE2009-11289.

Novel polypyrrole-polylactide blends were fabricated and characterized using compression molding, salt leaching, and in situ polymerization. Open-porous polylactide samples were fabricated using compression molding and salt leaching techniques with varying salt-to-polymer mass ratios of 3:1, 6:1, and 9:1. The samples then underwent in situ polymerization of pyrrole and iron (III) chloride to obtain a uniform coating of polypyrrole. Characterization of these novel composites comprised of their physical, mechanical, and electrical properties. With increasing salt-to-polymer mass ratio, it was found that the relative density decreased, the open porosity increased while pore size and pore density generally remained independent. The polypyrrole coating did not have a significant effect on the structure of the pore network. Microscopic polypyrrole nodules were observed to be uniformly coated on the surface and sub-surface of the composites. The compressive modulus decreased with increasing salt-to-polymer mass ratios. In addition, the modulus of the coated 3:1 salt-to-polymer mass ratio sample was twice the value obtained for the uncoated sample while the modulus values for the 6:1 and 9:1 samples did not significantly change. The conductivity increased as the salt-to-polymer mass ratio increased. The relationships observed between the structure and resulting properties provided the basis for future development and characterization of these novel porous composites.

Commentary by Dr. Valentin Fuster
2009;():217-224. doi:10.1115/IMECE2009-11314.

This paper investigates the processing and its effects and the effect of multiwall carbon nanotube (MWNT) composition on the thermal, electrical and mechanical properties of polylactide (PLA)-MWNT composites. The composite films were prepared by a solvent casting process using two solvents, chloroform and 1,4-dioxane. The dispersion of the MWNTs in PLA was examined using a scanning electron microscope and was found to be more improved when 1,4-dioxane was used as the solvent as compared to chloroform. The thermal characteristics of the composites were examined on Differential Scanning Calorimetry and Thermo-gravimetric Analysis. Composites prepared using 1,4-dioxane had greater improvements in composite decomposition temperature, glass transition temperature and displayed faster crystallization kinetics. The mechanical properties of the composites were tested in uniaxial tension. Composites prepared using chloroform had a lower modulus than composites prepared using 1,4-dioxane. The electrical AC conductivity of the composites was measured over a broad frequency spectrum. Composites prepared using 1,4-dioxane displayed electrical percolation at 0.5 wt.% MWNT in PLA while percolation was absent in 0.5 wt.% MWNT composites prepared using chloroform.

Commentary by Dr. Valentin Fuster
2009;():227-234. doi:10.1115/IMECE2009-11411.

As the shape memory material Nitinol (55% Nickel – 45% Titanium alloy) emerges to find more and more applications in engineered products, understanding the effects of material processing becomes increasingly important. Its mechanical behavior is highly non-linear and is strongly dependent on alloy composition, heat treatment history and mechanical work. Published Nitinol literature is almost exclusively related to processing and testing of thin wall, very small diameter tubing and wire devices, usually exhibiting superelastic characteristics. In strain-controlled tension-compression testing of pseudoelastic Nitinol shape memory wires, compression recovery forces were found to be markedly higher than tension forces. However, most experimental studies of the thermomechanical behavior of Nitinol (NiTi) to date have been conducted in uniaxial tension on wire devices. There is a dearth of information in the literature regarding the compression recovery of solid blocks of Nitinol. Questions exist on whether or not solid, “bulk” Nitinol products when deformed in compression will exhibit shape recovery characteristics? The potential for shape recovery of compressed solid blocks of Nitinol products, which could have large stress-strain outputs, can enable the design of novel devices in many industries. The motivation for this research is to provide the first characterization of the shape recovery effects of “bulk” Nitinol material under compressive deformation modes versus the often practiced and well understood tensile loading of wire and thin wall tubing.

Topics: Compression , Shapes , Tension
Commentary by Dr. Valentin Fuster
2009;():235-242. doi:10.1115/IMECE2009-11509.

The competition on the international markets pushes manufacturers towards shorter design cycles and decreasing manufacturing times and costs for their products. This trend generates a demand for smart, flexible and faster machining systems, easy to set up and configure, which are able to drastically reduce machining time and improve the final accuracy. This paper rises from these considerations evaluating the possible application of multifunction materials in machine tool (MT) design and building. These solutions can provide a fundamental impact on functionality and reliability of a manufacturing system. In particular, use of innovative materials in today’s technology continues to grow steadily. Numerous reasons for this growth include light weight, superior insulating abilities, energy absorbing performance, excellent strength/weight ratio and low cost. This paper aims to investigate a possible application of multifunction materials in realisation of structure components for Machine Tools. There are many aspects that affect the machining accuracy and the cutting conditions of a high performance MT. The most important issues are related to the static, dynamic, mechatronic and thermal behavior of the machines. In particular, a strict requirement that a machine tool has to fulfill in order to drastically reduce operating time while improving the final accuracy is the thermal stability. This paper shows a complete study and testing validation on prototypes (plates and beam) based on sandwiches with core made of metal foam (open and closed cells) materials impregnated by a PCM (Phase Material Change) wax. Metal foams represent a class of materials with low density and novel physical, mechanical, thermal, electrical and acoustic proprieties. They offer potential for lightweight structures, for energy absorption and thermal management. PCMs are latent heat storage materials that absorb heat keeping constant the temperature of a machine component in a defined time range. The authors have designed, realized and tested the prototypes developing thermal trials, and then evaluating the comparison between experimental data and simulative analysis (FEM). The trials consisted to process the prototypes at a variation of temperature in order to assess the PCM proprieties to absorb heat and maintain thermal stability in a defined time range. The paper shows also a simulative study on PCM material behavior and their application in MT design supported by experimental trials and data analysis. The significant advantages and perspectives that can be obtained in applying of these MT structures complete the developed study.

Commentary by Dr. Valentin Fuster
2009;():243-245. doi:10.1115/IMECE2009-11805.

Recent advancements in the field of nano-technology focused attention on developing materials with new and useful characteristics. In particular, there is interest in designing nanocomposite thermites for combustion synthesis applications. The composite material consists of nano-scale particles that are in nearly atomic scale proximity but constrained from reaction until triggered. Once initiated, the reaction will become self-sustaining and a new intermetallic alloy product will be produced. An example of this type of reaction is between Ni and Al such that a nickel-aluminide alloy is produced (Eq. (1) [1].

Commentary by Dr. Valentin Fuster
2009;():247-250. doi:10.1115/IMECE2009-11849.

The P-type perovskite oxides La1−x Srx CoO3 (x∼0.05) are a promising group of complex oxide thermoelectric materials. The thermal electric properties of these complexes are expected to increase significantly when their dimension was reduced to nano scale. In this project, the La1-x Srx CoO3 (x∼0.05) nanofibers, with diameters in the range of ∼30–80 nm, were prepared by the electrospinning process. Various substrates such as aluminum foil, silicon dioxide, and a specially designed tester were used to collect and anneal the nanofibers. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were conducted to characterize these thermoelectric nanofibers. Finally, a thermoelectric property tester device was developed and used to measure the voltage output of the nanofibers due to the Seebeck effect. The detected signal was at the mV level and the Seebeck coefficient was positive.

Commentary by Dr. Valentin Fuster
2009;():251-257. doi:10.1115/IMECE2009-11886.

In this paper, we present a multiple mode sensing methodology to detect active corrosion in aluminum structure utilizing the broadband piezoelectric wafer active sensors. This method uses ultrasonic Lamb wave complemented with the electromechanical impedance measurement to detect, quantify, and localize the corrosion progression in plate-like structures. The ultimate objective of this research is to develop in-situ multimode sensing system for the monitoring and prediction of critical aerospace structures that can be used during in-service period, recording and monitoring the changes over time. The test experiments were conducted on an aluminum plate installed with a five sensor network using 7-mm piezoelectric wafer active sensors. The corrosion was emulated as material loss of an area of 50mm 38mm on the other surface of the plate. Detection of corrosion and its growth was first conducted using the Lamb wave method in pitch-catch mode. The corroded area resulted in a thickness loss on the Lamb wave propagation and caused the amplitude and phase changes in the structural responses. The experimental data was first evaluated by the statistics-based damage indicator using root mean square deviation. Though the damage indicator is able to detect the presence of the corrosion and identify the corrosion location quantitatively, it failed in giving the right indication of corrosion development. A more corrosion signal processing based method, the cross time-frequency analysis, was proposed and used to analyze the phase characteristics of the data set. This cross time-frequency analysis was found more reliable and precise for detecting the corrosion progression compared with the damage indicator method.

Commentary by Dr. Valentin Fuster
2009;():259-267. doi:10.1115/IMECE2009-12861.

A hybrid material consisting of an interpenetrating phase composite of aluminum foam and thermoplastic polymer was made and tested for its basic tensile mechanical properties. The material was made by injection molding a polymer (two polypropylenes and an acetal were used) through a Duocell aluminum foam (10% relative density and 10, 20 and 40 pores per inch linear densities). The material is referred to as an Aluminum Foam Polymer Composite (AFPC) and involves the aluminum foam and the polymer occupying the same volume. The continuous, interconnected morphologies of the two phases (aluminum foam and polymer) sets this type of material apart from regular composites. The AFPC exhibited an increase in stiffness, a reduction in strength and less ductility than the parent polymer. A basic mathematical model and a discussion of the physics were used to shed some light on the behavior of this material.

Commentary by Dr. Valentin Fuster
2009;():269-275. doi:10.1115/IMECE2009-12899.

The formation of the spinel of magnetite and chrome oxide, is a very complex process, especially with the scale removal effect in flowing lead bismuth eutectic (LBE) nuclear coolant. This paper studied the formation and the protection of the spinel of magnetite and chrome oxide on stainless steel, in different environments at a mesoscopic level. The role of the alloying element has been analyzed. The formation of the spinel of magnetite and chrome oxide and the scale removal effect are simulated using a stochastic cellular automaton method. The protection of this spinel layer to the structural materials has been analyzed.

Commentary by Dr. Valentin Fuster
2009;():277-287. doi:10.1115/IMECE2009-13302.

This paper reports the dependency of specific heat and ballistic thermal conductance on geometry and size in freestanding isotropic non-metallic crystalline nanowires and nanotubes having varying wall thicknesses and outer diameters. The analysis is performed using real dispersion relations found by numerically solving the Pochhammer-Chree frequency equation of a tube. The frequency equation is derived from the 3D cylindrical elastic wave model with stress free boundary conditions on both the inner and outer wall surfaces. Dimensional dependencies are distinctly noticeable and vary with specimen geometry and temperature. Trends in dimensional transition points are seen by varying the ratio of inner to outer nanotube radius (γ) for a 5 nm fixed outer diameter. With increasing γ, heat capacity and ballistic thermal conductance is shown to collapse onto that of a solid nanowire. Additionally, thermal properties of thick-walled nanotubes (γ = 0.5) having diameters of 5 nm, 10 nm, 15 nm, and 20 nm, are also investigated in this study. Increasing the diameter of a nanotube with a fixed γ is shown to have a similar mechanistic effect as fixing the outer diameter and thinning the tube wall.

Commentary by Dr. Valentin Fuster
2009;():289-292. doi:10.1115/IMECE2009-10570.

Powder metallurgy and liquid metallurgy techniques were used to fabricate Mg reinforced with different volume fraction of nano-size MgO particles. A higher volume fraction of MgO particles could be added into the Mg matrix when the liquid metallurgy technique was used. Microstructural analysis was carried out to examine the distribution of the nanoparticles in the Mg matrix when different processing routes were chosen. Individual particles together with sparsely distributed agglomerations could be discerned in the Mg matrix for both processing routes. Mechanical properties results revealed that a more substantial improvement in macrohardness and tensile properties could be achieved by using the liquid metallurgy route where a higher amount of nano-size MgO particles could be incorporated.

Commentary by Dr. Valentin Fuster
2009;():293-300. doi:10.1115/IMECE2009-11459.

In this study, three kinds of carbon nanofiber sheets were made through a high-pressure filtration system: pure carbon nanofiber, carbon nanofiber with polyhedral oligomeric silsequioxane (PCNS) and carbon nanofiber with Cloisite Na+ clay (CCNS). Then these sheets were incorporated onto the surface of glass fiber reinforced polyester composites through resin transfer molding process. The samples were analyzed with scanning electron microscopy (SEM), thermal gravimetric analyses (TGA). The fire retardant performance of the laminates was evaluated with cone calorimeter test at an external radiated heat flux of 50kw/m2 . The results of laminates with PCNS indicated that the fire performance was impaired when comparing with the case of pure carbon nanofiber paper. However, in the case of CCNS, the primary results showed a pronounced improvement of the fire performance was observed. The possible mechanism was also discussed in the present study.

Commentary by Dr. Valentin Fuster
2009;():301-306. doi:10.1115/IMECE2009-10534.

In this paper, the effects of low-velocity impact on the E-Glass Epoxy woven composite laminates under tensile preload are presented. Due to the low-velocity impact loading, laminate suffers an extensive internal damage such as delaminations and the damage on the back face. The effect of preload can significantly change the impact behavior and progressive damage mechanics. Therefore the study of impact damage susceptibility of these woven composite laminates under tensile preload (corresponding to tensile strain) is increasingly important. While considerable experimental and analytical studies have been made on the low velocity impact phenomenon, very little work is reported in the area of effect of preloads on the damage mechanics for E-Glass Epoxy woven composite laminates subjected to low velocity impact. A detailed finite element mosaic model was developed using Virtual Proving Ground (VPG) software. Dynamic analysis was performed using LSDYNA® finite element software. A plate consisting of 10 layers of E-Glass/EPON 862-W (10EG) was modeled using three dimensional orthotropic elastic brick elements. Preload boundary conditions were simulated using in-plane displacement for three different incremental values (0.08% strain, 0.16% strain and 0.24% strain) representing realistic assembly conditions. The simulation results were compared for their maximum load carrying capacity. It was observed that with increase in preload, laminate looses its maximum load carrying capacity.

Commentary by Dr. Valentin Fuster
2009;():307-312. doi:10.1115/IMECE2009-10637.

The paper addresses a challenging problem of developing technology for heat exchanger tubes embedded in ceramic composite matrix. Functionally graded composite tubes, made using physical vapor deposition (PVD) process, are required to have diffusion barrier layers, withstand high temperature, and be impermeable to hydrogen. The work addresses mathematical modeling of the deposition of metallic vapors from multiple targets on a cylindrical substrate to simulate the PVD process in manufacturing such tubes. Materials used for the deposition are Molybdenum and Niobium because they have shown good formability, strength, toughness and ductility over a wide range of temperatures. Commercially available software FLUENT was used to model the process. Prediction of condensation of vapors from metal ingots occurs in varying proportion along the circumference of the tube, resulting in submicron layers of different materials of varying thicknesses being ingrained into each other. Results are presented for patterns of materials showing continuously changing relative concentration of deposited metals over a stationary and rotating cylindrical substrate.

Topics: Vapors , Metals
Commentary by Dr. Valentin Fuster
2009;():313-321. doi:10.1115/IMECE2009-10914.

This study dealt with the effect of hybridization of jute fiber and glass fiber on the mechanical properties of fiber reinforced thermoplastics injection moldings. In the glass/jute hybrid materials the weight fraction of glass fiber was fixed at 10wt% and that of jute fiber was varied from 5wt% to 30wt%. Dumbbell-shaped specimens were prepared by injection molding, and the static tensile tests were performed with acoustic emission (AE) monitoring. AE monitoring was conducted to understand the fracture behaviors of glass/jute hybrid materials. By adding the glass fiber to jute fiber reinforced plastics the tensile strength was improved. However, too much content of jute fiber could not achieve the improvement of strength because the uniform distribution of glass fiber was restricted by too much bulky jute fiber. After tensile test the fiber distribution on the fracture surface was observed. Based on the fiber distribution of jute fiber and glass fiber the strength prediction was attempted by introducing the rule of mixture.

Topics: Glass
Commentary by Dr. Valentin Fuster
2009;():323-334. doi:10.1115/IMECE2009-11599.

The goal of this work is to develop and investigate the properties of a new type of multifunctional composite which is based on multi-walled carbon nanotubes (MWCNT). The composite was prepared from a paper like MWCNT film which was sandwiched between two adhesive layers. Both two point probe and four point probe methods were used to test its mechanical strain sensing properties. The Young’s modulus and shear modulus of MWCNT film composite were acquired by the nanoindentation test and direct shear test. A free vibration test was also performed to investigate its structural damping properties. A new model/configuration for sandwich structural vibration control was then proposed based on the MWCNT experiments results. In this new configuration, a cantilever beam covered with MWCNT composite on the top and one layer of shape memory alloy (SMA) on the bottom was used to illustrate this concept. The MWCNT composite simultaneously serves as free layer damping and strain sensor, and the SMA acts as actuator. Simple on-off controller was designed for controlling the temperature of the SMA so as to control the SMA recovery stress as input and the system stiffness. Both free and forced vibrations were analyzed. Simulation work showed that this new configuration for sandwich structural vibration control was successful especially for low frequency system.

Commentary by Dr. Valentin Fuster
2009;():335-339. doi:10.1115/IMECE2009-11632.

Carbon nanofiber (CNF) papers, when incorporated onto the surface of glass fiber reinforced polyester composites, were known to enhance the fire-retarding capability by decreasing the peak heat release rate (PHRR) and slowing down the mass loss. In this experimental study, attempts were made to understand the thermal degradation mechanisms of the composites and nanocomposites. The temperature distribution within the composite substrate should be determined because the degradation rate is related to the temperature. The composite was prepared through vacuum-assisted resin transfer molding (VARTM) process. Samples of glass-polyester resin composites were investigated. Thermal conductivity data was calculated from embedded thermocouples on the composite for real-time temperature measurement. Mass loss data was collected using thermal gravimetric analysis on resin and CNF paper samples. These results should help to further understand the depth and degree of the degradation and provide an understanding of thermal properties in composites.

Commentary by Dr. Valentin Fuster
2009;():341-350. doi:10.1115/IMECE2009-11706.

Thermal barrier coatings (TBCs) have been utilized for more than four decades to increase the efficiency and durability of aircraft engines as well as land based gas turbines. Though the function of the thin TBC layer is heat insulation, it is critically important for it to maintain adherence in service. In this paper, we address some fundamental aspects of TBC debonding failure in electron beam physical vapor deposition (EB-PVD) TBC systems that had been considered in a previous study. We demonstrate that the energy release rate formulation for EB-PVD TBC systems based on as-processed conditions and a thin thermally grown oxide (TGO) layer overestimates the energy release rate for exposed TBC systems having thicker TGO layers. A modified formulation is given, applicable to exposed TBC systems. A finite element contact and fracture model is used to validate the formulation as well as study crack mode mixity. Mode II interfacial cracking is shown to be dominant for practical TGO thicknesses seen in exposed EB-PVD TBC systems.

Commentary by Dr. Valentin Fuster
2009;():351-358. doi:10.1115/IMECE2009-12188.

Electrospinning is regarded as an efficient process to form sub-micron and nano level fibers consistently in a simple laboratory scale setup. The process has excellent potential for scalability and for the structural applications of integrated electrospun fibers in polymer hybrid composites. In our on going work, the mechanical characterization of these hybrid composites with integrated electrospun fibers revealed significant variations based on the sintering temperature and the morphology of the formed electrospun fibers. The morphology (in particular, the fiber diameter) depends on the process parameters of the electrospinning process. This paper investigates the influence of two electrospinning parameters namely: Distance between spinneret and collector plate and voltage. Four voltage levels were selected varying from 15KV to 18 KV in the increments of 1KV. The spinneret to the collector plate distance was varied from 70 mm to 100 mm in 10 mm increments. Thus, a total 16 combinations of these parameters were studied keeping other parameters constant. The objective is to find the optimal voltage and distance combinations that produce smallest electrospun nano fiber diameters consistently. From each voltage-distance combination, the diameter of the deposited fibers was sampled at 50 different points using the morphological image data obtained with a scanning electron microscope (SEM). The analysis of experimental data indicated four favorable voltage-distance combinations that give smallest diameter size of electrospun nano fibers consistently. These four set of parameters were, 15KV and 70 mm; 15KV and 100 mm; 18 KV and 70 mm; and 18KV and 100 mm. The least diameter of fiber was observed and measured for a voltage distance combination of 18KV and 70 mm. The least diameter observed for these parameters can be attributed to the higher applied voltage resulting into higher bending instability causing the reduction in diameter of fibers. Another reason for reduction in fiber diameter is, when the distance between spinneret and collector is increased there is more space for elongation of fibers. With more increase in length of fiber, there is higher reduction in diameter of electrospun fibers. To correlate these process variations of electrospinning to the morphological properties of electrospun fibers, design of experiments study was carried out. It has been attempted here to investigate if there is any correlationship between the morphological property of electrospun fibers and properties of two phase composite. These investigations will provide an insight on the relationship between the process parameters — morphology — and the associated characterized macroscopic properties of the formed composites. Results from the stochastic modeling for variations in the fiber diameter due to the variations in the voltage and the distance correlate well to the ARMA (6,5) stochastic model. Greens functions for the model were derived and showed the stability of the electrospinning process.

Commentary by Dr. Valentin Fuster
2009;():359-364. doi:10.1115/IMECE2009-12204.

In this paper, nonlinear radial and hoop thermoelastic stress analysis of rotating disk made of functionally graded material (FGM) with variable thickness is carried out by using the finite element method. In this method, one-dimensional second order elements with three nodes have been used. The geometrical and boundary conditions are in the shape of nonexistence of the pressure (zero radial stress) in both external and internal layers and zero displacement at the internal layer of rotating disk. Furthermore, it’s assumed that heat distribution is as second order curve while material properties such as elasticity modulus, Poisson’s ratio and thermal expansion coefficient vary by using a power law versus radius of the disk and also vary with the temperature. In a numerical example, the displacements and stresses for various powers (N) and the angular velocities have been calculated in according to the radius. It’s obvious that by increasing the values of the power (N) and the angular velocity, the value of displacements and stresses will be increased consequently. Finally, the effect of varying the thickness and the dependency and in-dependency of the material properties on the temperature has been considered.

Commentary by Dr. Valentin Fuster

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