This study deals with the durability tests of a new copper plated electrode process for self-sensing or self-healing Carbon Fiber Reinforced Plastic (CFRP) composites. The self-sensing or self-healing CFRP composites adopt carbon fibers as sensors or actuators. The electrical contacts at the electrodes have a significant effect on the self-sensing or self-healing ability. This research proposes a new electric copper plated process for fabricating reliable electrodes. Using single-ply specimens, electrical contact resistances after cyclic loading are measured. The cyclic loading test is performed to investigate the long term durability of these new electrodes. The new copper plated electrode was found to have high durability after cyclic loading and is appropriate for the practical self-sensing or self-healing CFRP composites.

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The interface stress distributions in composite cylinders of steel (solid cylinder) and epoxy (hollow cylinder) under push-off loads are analyzed using axisymmetrical theory of elasticity as a three-body contact problem. In the numerical calculations, the effects of Young’s modulus and the diameter of solid cylinder on the interface stress distribution are examined. In addition, the effects of the diameter of supported hollow cylinder and the stress distribution due to the applied push-off loads are also examined. It is found that the normal stress at the interfaces increases as Young’s modulus of solid cylinder decreases, the diameter of solid cylinder and the diameter of supported hollow cylinder increase. It is also found that the shear stress at the interfaces increases as the diameter of supported hollow cylinder increases, Young’s modulus and the diameter of solid cylinder decrease. Singular stresses occur at the edges of the interfaces. A valid method for estimating the singularity is proposed and the discussion is made. Using the interfaces stresses obtained from the numerical analysis and analogous tests, the push-off strength of composite cylinders is estimated. The experiments to measure composite cylinders strength are carried out. It is seen that a rupture initiates at the lower edge of the interface area when the push-off loads are applied to the upper end of solid cylinder. For verification of the present analysis of the interface stress distributions, finite-element method (FEM) is also carried out. The numerical results of the interface stress distributions and the strength are in fairly good agreement with the experimental results and the FEM results. The axisymmetrical theory of elasticity is more rational compared to the shear lag theory in examining the stress singularity and considering the normal stress and shear stress at the interfaces at the same time. Finally, as an example, it is observed that the weight of composite cylinders is lighter by 48.1% than that of the structure with the same of steel material for obtaining the same strength.

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This paper discusses the reliability assessment of advanced structures such as micro/nano structures, electronics packaging for modern electronic devices, high temperature structures such as nuclear power plants, rocket engines for space application. Characterization of advanced materials includes free-standing electrodeposited nano-crystalline nickel thin film, polysilicon, and piezoelectric thin film for MEMS/nano structures. Lead-free solders under pseudo-power cyclic thermal loading, impact loading and mechanical bending loading were evaluated for reliability assessment of the advanced electronic packaging. Reliability assessment of Cu/SnAg double bump structures was performed for the 150µm pitch flip chip electronic packaging application. The 316L austenitic stainless steel for high-temperature components application such as in the primary side of liquid metal cooled fast breeder reactor (LMFBR) was tested under various temperatures where dynamic strain ageing occurs. The effects of dynamic strain ageing on the tensile behavior and fatigue behavior of 316L stainless steel have been identified.

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Magnetostrictive materials have been widely used in sensors, actuators and transducers for decades. However, their applications are limited by the nonlinear response to both the prestress and the environment temperature. In that case, systematical study on magneto-thermo-mechanical behaviors of magnetostrictive materials is needed. In this paper, a new magneto-thermo-mechanical experimental apparatus is developed by adding circulating oil bath system to our magneto-mechanical device. Magnetization and magnetostriction processes of Terfenol-D under different temperatures and prestresses are investigated. Strong magneto-thermo-mechanical coupling of giant magnetostrictive materials is shown and discussed. Magnetization process is depressed with the increase of both prestress and temperature, while low-field magnetization and magnetostriction are not sensitive to temperature. The results are of importance to theoretical analysis and industrial applications.

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This paper deals with the mechanism of electrical resistance change observed after delamination cracking of a thick Carbon Fiber Reinforced Polymer (CFRP) laminate. In a previous paper, the current shut-off caused by the delamination crack increased the electrical resistance for a thin laminate, and the effect of piezoresistance caused by the residual strain relief was small compared with the shut-off effect. For the thick CFRP, a dent is made because of the high indentation compression load at the loading point. The present paper measures the effect of the dent experimentally and estimates the electrical resistance increases caused by the shut-off effect and piezoresistance effect using Finite Element Method (FEM) analyses. The estimates are compared with the experimental results of the thick CFRP laminate. As a result, it is established that the effect of the dent (which causes a decrease of electrical resistance) is larger than the effect of the shut-off (which causes an increase of electrical resistance) for the thick CFRP laminate.

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There have been several attempts to solve Hertz equation for curved surface contact problem. One application of Hertzian contact problem is to determine the contact properties between wheel and rail. It is important to understand the contact between wheel and rail so that excessive wear can be avoided and train accidents can be minimized. In this work, an attempt has been made to solve Hertzian contact for small radius of curvature using a simple newly invented formula. A finite element modeling was also performed to observe the variations of maximum contact stress in rail with respect to the change rail radius of curvature. The invented formula was to modify the formula of Fischer et.al especially for the major and minor axis so that a more accurate result was obtained in determining the contact dimensions and maximum contact pressure.

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The contribution deals with the CFD (Computer Fluid Dynamics) thermal analysis of the electromotor frame performed with the aim to reach the better cooling ability of the electromotor cooling system. The first step before the optimization of cooling properties is to create the computer model which describes well the thermal processes in the motor and uses possibly highest number of simplifications leading to the shorter solution times. One possible approach how such a model can be created is described in this contribution. The mechanical and electrical components producing the heat during the operation of the electromotor are substituted by the heat fluxes applied on the walls of electromotor frame. The method how to locate places where the appropriate heat flux should be applied is presented. The approach is based of the iterative process whereas the surface temperatures of the electromotor frame are calculated via finite volume method for certain heat flux distribution and results are compared with values obtained by measurements via thermovision camera and thermoelements. The process is finished after the surface temperature corresponding to the real state is reached. This adjusted model is then expected to be used in the optimization process leading directly to the required reduction of the motor surface temperature and mass.

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The contribution presents the cooling rib optimization on the two numerical models with the aim to show the influence of used model symmetry geometry on the design optimization problem properties. The parameters of used computational models (the models differ in used symmetry conditions) and the application of boundary conditions are presented. The optimization is based on FEM (Final Elements Method) structural thermal analysis and is done by ANSYS Workbench v11 software package. The obtained results show the necessity to take into account the authentic rib space arrangement in model simulations of optimization problem.

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Asphalt mixture is described as an elastic and viscous material. Hooke’s law and the Bailey-Norton formulation are respectively used to characterize its elastic and viscous behaviors. A numerical algorithm frame is constructed to analyze nonlinear and time dependent deformation behavior of asphalt mixture. The model parameters are determined by the uniaxial compressive creep experiments and the algorithm is validated by comparison between the numerical results and the rutting experiments. The algorithm is used to analyze rutting deformations in different types of asphalt mixture specimens under cycled wheel loads. Some preliminary studies on effects of aggregate gradation on the rutting deformation in asphalt mixture samples are conducted. Finally, some conclusions are given.

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This paper discusses the optimum pore arrangements on the porous low-k dielectrics through Genetic Algorithm (GA) and U^* analyses. Higher performance large scale integration (LSI) requires lower dielectric constant to decrease line-to-line capacitance. Recently, porous low-k dielectrics are introduced for low-k dielectrics because of its ultra lower dielectric constant. However, their poor mechanical strength causes fractures of porous low-k dielectrics during Chemical Mechanical Polishing (CMP) process. Therefore, it is important to develop porous low-k dielectrics that have low dielectric constant and high mechanical strength. To make optimum pore arrangements, GA was introduced and porous structures in the dielectrics were made. Also, the obtained results were evaluated by the index U^*. The index U^* expresses a degree of load transfer or dielectric force transfer. Through those analyses, the pore arrangements with low dielectric constant and high stiffness were proposed. The obtained results showed that pores were aggregated and arranged obliquely. This is because these structures have an advantage to transfer the load and hinder the dielectric force transfer efficiently.

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The bolted joint is a common assembling method for carbon fiber reinforced plastic (CFRP) members. However, cracks or plastic deformation can occur around bolt holes of CFRP members even when employing low fastening forces. As a result, CFRP failure occurs around bolt holes because of bearing forces, and the strength of a CFRP joint is reduced. To address this problem, we change the configurations of washers and insert a thin sheet having a high friction coefficient between CFRP members. In friction coefficient measurements, the insertion of sandpaper was found to be the most suitable method for increasing friction forces at the interface between CFRP members. Three-dimensional finite element method analyses were conducted to investigate the effect of washer configurations in terms of the maximum allowable fastening force and the joint strength. From these analyses, the cone washer was found to be the most effective design for increasing the joint strength. In the full model analyses, the failure strengths of proposed CFRP bolted joints were higher than those of normal CFRP bolted joints. The verification tests for the proposed joint were conducted according to ASTM D5961. It was observed that the load at failure for the proposed bolted joint was about 45 % greater than that for the conventional joint.

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AZ91 magnesium alloy in different heat treatment conditions was impacted by GCr15 steel projectile (2 km/s, power gun) and 2017 Al alloy projectile (3 km/s, two-stage light gas gun). Deformed bands, plastic flow and a wealth of cracks were observed near the crater in as-cast magnesium alloy impacted by GCr15 steel projectile, while for the solution treated alloy, both deformed and transformed bands were observed accompanied by fewer cracks near the crater. Upon higher velocity impact using two-stage light gas gun, many cracks and severe deformed areas containing a number of elongated grains were observed near the crater for both hot-forged and solution-treated targets, while fewer adiabatic shear bands could be found. Most of these shear bands were located at the end of cracks. The strain hardening at different zones under the crater was also investigated.

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Influence of heat aging on fatigue crack growth properties of vulcanized natural rubber used in engine mount applications were studied based on fracture mechanics approach. Heat aging of the pure shear specimens was carried out at 70°C and 100°C for a period ranging from 24h to 168h. The tearing energy at various tensile strains was calculated from the stress-strain curves obtained from the static tests of the specimens. Fatigue crack growth rate was calculated from the cyclic tests of the specimens at constant displacement conditions and results were presented as a function of tearing energy. The crack growth rate at a given tearing energy was higher for specimens aged at 100°C and increased with the increase in aging period. The crack growth rate was not much affected for the specimens aged at 70°C. Also, the effect of heat aging on molecular mobility was studied by measuring spin-spin relaxation time T₂ using pulsed Nuclear Magnetic Resonance (NMR).

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In this study, we examine the variation in residual stresses in polymer matrix composites with cyclic changes in hygrothermal environments by measuring the axial stresses in the fiber of single-carbon fiber/epoxy resin model composites using Raman microspectroscopy. To change the temperature and water absorption in the specimens separately and simultaneously, the specimens were (1) heated and cooled at atmospheric environment, (2) immersed in water and dried at room temperature, and (3) immersed in hot water (80°C) and cooled to room temperature in water and then dried. All specimens were thus restored to their initial states and then evaluated. In the cases of (1) and (2), the fiber stresses reverted to almost the same as their initial states, but in the case of (3) the axial stress after hygrothermal cyclic change was more compressive compared to the initial state. The differences among the results of the three cases are discussed based on the fiber stresses at elevated temperature, which were evaluated by Raman microspectroscopic measurement performed at temperatures ranging from room temperature to those above the glass-transition temperature of the epoxy matrix resin.

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The objective of the study is to construct a sensor fusion system for tool-condition monitoring (TCM) that will lead to a more efficient and economical drill usage. Drill-wear monitoring has an important attribute in the automatic machining processes as it can help preventing the damage of tools and workpieces, and optimizing the drill usage. This study presents the architectures of a multi-layer feed-forward neural network with Levenberg-Marquardt training algorithm based on sensor fusion for the monitoring of drill-wear condition. The input features to the neural networks were extracted from acoustic emission (AE), vibration and current signals using the wavelet packet transform (WPT) analysis. Training and testing were performed at a moderate range of cutting conditions in the dry drilling of steel plates. The results indicated that the supervised neural networks were effective for drill-wear monitoring and the output of the neural networks can be directly utilized for the planning of tool life management.

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The extrusion strengthening process and mechanism of a CuW80/Cu solid contact material, which was sintered and infiltrated prepared by powder metallurgy, were investigated. Moreover, the numerical simulation of extrusion process of the CuW80/Cu solid contact material was carried out by means of a finite element method. The results show that the hardness of the tail Cu in the CuW80/Cu solid contact material was improved significantly after extrusion, which is greatly dependent on the squeezing location and deformation of the tail Cu. It indicates that the farther from the CuW80/Cu interface or the closer to the surface of sample is, the higher hardness of the tail Cu after extrusion has. By a finite element method, the numerical simulation is successfully used to analyze the stress and strain field distribution as well their changes in extrusion process of the CuW80/Cu solid contact material. The equivalent plastic strain simulation coincides well with the results of micro-hardness tests, which can provide a theoretical basis for extrusion strengthening of the tail Cu in the CuW80 / Cu solid contact material.

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Nanoindentation tests were conducted for polyimide (PI) coating / Si substrate specimens and the energy release rates were evaluated as the interfacial strength. The energy release rate due to coating delamination was obtained from the load-displacement curve by the method proposed by Omiya et al. Three specimens that have different thickness and another kind of specimen which is the same as the thinnest coating but with an additional layer were prepared. The dependencies on the coating thickness and delamination propagation rate were investigated. The interfacial strength of the only thinnest coating case is underestimated, since small scale yielding conditions were not satisfied. The value of the interfacial strength between PI coating and Si substrate increases with increasing of the delamination propagation rate. The value becomes constant when the delamination propagation rate exceeds around 7.0×10^-3 mm/s. By considering the unloading curve, the corrected evaluation method for interfacial strength was proposed. The interfacial strength evaluated by the corrected method converge for all specimens cases.

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In this study, a numerical method for the identification of the Young's modulus of linear elastic coated materials from continuous indentation test is first presented. The identification is based on an inverse analysis where the minimization of a cost functional is performed by a gradient descent algorithm. The main result is the computation of cost function gradient by using a direct differentiation technique, resulting in a time-saving method compared to the widely used finite difference method. The validity and illustration of this approach is shown through several numerical examples. The second part of this article is dedicated to the identification of elasto-plastic thin films Young's modulus. A new method is proposed, where the inverse analysis relies only on finite element computations for elastic materials.

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In order to develop a brain spatula or a brain retractor made of a shape memory alloy (SMA), the bending characteristics of the brain spatula of TiNi SMA made by the precision casting were discussed based on the tensile deformation properties of the existing copper and the TiNi rolled-SMA. The fatigue properties of both materials were also investigated by the plane-bending fatigue test. The results obtained can be summarized as follows. (1) The modulus of elasticity and the yield stress for the cast and rolled SMAs are lower than those for the copper. Therefore, the conventional rolled-SMA spatula and the new cast-SMA spatula can be bent easily compared to the existing copper-brain spatula. (2) With respect to the alternating- and pulsating-plane bending fatigue, the fatigue life of both the copper and the SMAs in the region of low-cycle fatigue is expressed by a power function of the maximum bending strain. The fatigue life of the conventional rolled SMA and the new cast SMA is longer than that of the existing copper. The fatigue life of the new cast and rolled SMAs in the pulsating-plane bending is longer than that in the alternating-plane bending. (3) The above mentioned characteristics of the SMA-brain spatula obtained in this study can be substantially applied to the development not only for the brain spatula but also for other retractors and instruments used in other surgery operations.

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Fatigue strengths of polypropylene composite materials reinforced by 20wt% talc and 20wt% glass fiber were not improved for plate specimens made from manufactured pallets by using newly developed waste plastics recycling apparatus. On the contrary fatigue strengths of polypropylene composite materials reinforced by 25wt% Talc and 20wt% GF were improved for plate specimens made from injection molding machine. It can be concluded from fracture surface observations that fatigue strength of polypropylene composite materials reinforced by filler materials such as talc and glass fiber can be improved by controlling the manufacturing process to obtain the tight interface between polypropylene and reinforced materials such as talc and glass fiber.

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Hydrogen concentration absorbed into material increases in long-term operation of hydrogen utilization machines. In this study, the effect of absorbed hydrogen on fretting fatigue strength was examined when the surface hydrogen concentration was sufficiently high. The concentration of absorbed hydrogen was changed by changing hydrogen charge time. The test material was pre-strained austenitic stainless steel SUS304. Hydrogen concentration at specimen surface was about 60ppm. Fretting fatigue strength was decreased and had a lower limit with increase of the hydrogen charge time. The amount of reduction of fretting fatigue limit due to hydrogen was 42% of fretting fatigue limit of uncharged specimen tested in air. In hydrogen gas, local adhesion between contacting surfaces occurred, and many small cracks emanated from both tips of the adhered part. These small cracks are one of the causes of the reduction of fretting fatigue limit.

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The effects of hydrogen on fatigue crack propagation behavior of short fatigue crack and crack closure behavior were studied using low alloy steel SCM440H. Fatigue crack propagation test using specimen which has a 50µm deep pre-crack was conducted at a frequency of 28Hz in air, vacuum and hydrogen gas. Hydrogen pre-charge was done by cathodic polarization method. The concentration of absorbed hydrogen was 0.83 ppm in hydrogen charged specimen and 0.06 ppm in uncharged specimen. The fatigue crack propagation rate of uncharged material was dependent on environments. The acceleration of fatigue crack propagation rate by absorbed hydrogen was about 2 to 5 times irrespective of environment. As a consequence, the fatigue crack propagation rate of hydrogen pre-charged material tested in air was the highest. The crack opening stress was higher in hydrogen gas and in vacuum compared with that in air. Fatigue crack propagation rate was summarized in two independent bands when plotted against effective stress intensity factor range. This means that the effects of environment (vacuum, air and hydrogen) and stress ratio (R = -1, 0, 0.6) could be explained by crack closure phenomenon. However, the acceleration of crack propagation by absorbed hydrogen could not be explained only by crack closure phenomenon.

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The behavior of fatigue cracks which propagated at some representative areas in the friction stir welded joint of aluminum alloy, AA6063-T5, was studied at both room temperature (RT) and 200°C. The experimental results showed that the fatigue crack propagation (FCP) rates were significantly different depending on the crack propagating area. The test temperature also affected the FCP rates remarkably. In all cases, the FCP rates in the weldment were higher than those in the parent metal. The difference could not be reasonably interpreted only from mechanical point of view in which the crack closure behavior was taken into account. Furthermore, the non-uniform distribution of hardness had insignificant effect on FCP rates. This study found that the microstructural inhomogeneity played more essential role in FCP behavior of FSW.

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Based upon understanding the effects of CSD and HIP processing on the mechanical properties and microstructure of the TiAl alloy, three point bending fatigue tests were carried out under load control at room temperature, and fatigue crack growth process and fatigue thresholds of the Ti-48Al-2Mn-2Nb alloys by CSD and HIP were investigated. The results show that the mean stress inducing fatigue crack initiation from notch tip and the stress intensity factor for the CSD TiAl samples are 346 MPa and 9.60 MPa·m^1/2, respectively, while 307 MPa and 8.67 MPa·m^1/2 for the HIP TiAl samples, correspondingly. The CSD TiAl samples show better fatigue crack growth resistance and higher fatigue threshold than that of the HIP TiAl samples. It indicates clearly that the lamellar structure has a better resistance to fatigue crack growth than that of duplex structure. The fatigue crack growth process and mechanism for the CSD and the HIP samples are discussed.

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Nylon 6 clay hybrid (NCH) is a nanocomposite of nylon 6 matrix reinforced with clay called Montmorillonite. It has characteristics of high strength, high stiffness and low gas permeability due to the dispersed Montmorillonite in nylon 6 matrix by the nanometer unit. However, methods of design and life evaluation have not been established because few studies on creep have been done. In this study, we conducted the tensile creep tests for 200 hours at room temperature using a servo-hydraulic testing machine. The creep viscoelasticity in nylon 6 clay hybrid has been analyzed and predicted by using the Burgers model and Findley power law. Both models can accurately express the creep viscoelasticity in the polymers. The simulating parameters and creep strain of each unit in Burgers model illustrated the influence of clay on the creep viscoelasticity. The creep strain predicted by the Burgers model is higher than that by the Findley power law.

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