The continuum damage mechanics is extended to cover the self-repair process as well as the damage process. The repair variable and its evolution equation are newly introduced to consider the repair process. In the constitutive modeling, the equation of creep based on kinematic/isotropic hardening theory is extended to take the effect of damage into account. The evolution equation of a repair variable is proposed, based on Dyson's equation of creep cavity growth. The validity of the proposed modeling is illustrated through the simulations for the self-repair process of two kinds of steels damaged by creep.

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In order to clarify the influence of applied normal load, relative sliding speed, surface roughness and materials Young's modulus and their cross influence on friction coefficient an analytical model is developed based on experimental results for obtaining friction function using response surface methodology. The friction coefficient (CoF) with the variation of the factor levels are investigated experimentally on a micro-tribometer machine. The design is performed using response surface method (RSM). The coefficient of friction (CoF) with the variation of the factor levels are investigated experimentally on a micro-tribometer UMT-2 machine. The machine is used to measure the friction force, normal force and the CoF. The second order mathematical model, in terms of the factors, was developed for the coefficient of friction (CoF) using response surface methodology (RSM). The significance of these factors on the CoF has been established with the analysis of variance. It is found that the relative sliding speed, surface roughness, quadratic term of the load, quadratic term of the speed, the interaction between the materials Young's modulus and roughness are significant model terms. An attempt has also been made to optimize the coefficient of friction and to find a region of the factors space in which operating requirements of CoF are satisfied.

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BMC (Bulk Molding Compound) is composed of UP (Unsaturated Polyester) resin, glass fibers, and bagasse fibers which have been obtained after squeezing sugar cane. Our purpose is to use the bagasse fibers as reinforcement and filler in BMC to fabricate composites by injection molding and injection compression molding. The mechanical properties of injection molding composites were improved after adding the bagasse fibers. Observing the fracture surface of the tensile test specimen through SEM, we could notice the glass fibers were penetrated into the bagasse fibers longitudinally. Along with UP resin solidifying, the glass fibers were firmly fixed in the bagasse fibers and finally united with them. This phenomenon could bring on the same effect as the glass fibers length was prolonged, so that the adhesion interface between fiber and matrix resin became larger, which leads to the increase in the mechanical properties. Otherwise, it was observed that UP resin sufficiently permeated the bagasse fibers and solidified. This also contributes to enhancing the mechanical properties drastically.

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We investigate the effect of interface stress on nanoparticles embedded in films, within the framework of continuum and interface elasticity. The study is motivated by the idea that elastic interactions among three-dimensional strained nanoparticles can lead to size and spatial uniformity of islands, during the growth of multilayered superlattices. This presents a promising avenue in the quest of constructing self-organized nanostructures. Islands, adatom-clusters, and quantum dots can be modeled as inhomogeneities embedded in a heterogeneous film substrate. While the film (bulk) is modeled as linearly elastic and isotropic, interfaces are treated according to Gurtin's theory of linear interface elasticity. In order to illustrate the role of a mechanical load, the system is subjected to uniaxial tension, applied at the remote boundary of the substrate. The displacement potentials methodology, i.e. Papkovitch-Neuber, Boussinesq, and Dougall potentials, coupled with interface elasticity yield an analytical solution. The elastic field is expressed in terms of several sets of spherical and cylindrical harmonics. The study illustrates clearly that interface elasticity introduces a size-effect. In addition, local stresses are significantly affected by the size and position of the nanoparticles.

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The paper studies the influence of compatibilizer (polypropylene-graft-maleic anhydride, PP-g-MA) on morphology and mechanical properties of polypropylene/zinc oxide composites. Polypropylene (PP) and zinc oxide (ZnO) composites were prepared by melt mixing technique in a twin screw extruder. The Young's modulus and impact strength of the composites increased as ZnO loading increased, but the impact strength was decreased with the addition of the compatibilizer. The tensile strength of the composites before and after adding compatibilizer was almost the same with the pure PP. The dispersion of ZnO in the matrix polymer was investigated using scanning electron microscope (SEM). The results obtained show that the addition of a small of PP-g-MA compatibilizer during melt extrusion improved the dispersion of ZnO particles.

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The effect of oblique functional gradation to thermal stresses in the semi-infinite body is studied theoretically. The rigorous solution is derived by the use of the variable separation and the stress function method. The material properties are assumed to be exponential functions of the position along the functionally graded direction. Two types of boundary conditions are considered, one is the prescribed heat flux on the heating surface and the other is the prescribed temperature on the same surface. The numerical calculations are carried out for ZrO₂ /Ti-6Al-4V functionally graded materials (FGMs). The numerical results of temperature and thermal stresses are illustrated with figures for different values of an oblique angle. Numerical results for the prescribed temperature boundary condition show that the temperature curve leans to the ceramic-rich side and the compressive stress decreases with increasing the oblique angle when the oblique angle varies from 0° to 45°.

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Residual stress is generated in ceramic thermal barrier coatings (TBCs), which were sprayed by a plasma spray technology, due to the difference in coefficients of thermal expansion between the coating and the substrate. Previous experimental results obtained by the X-ray diffraction method indicated that the residual stress at the ceramic coating surface is tensile and could lead to TBC failure such as cracking and spalling of the ceramic coating. In this study, a numerical model that can predict the residual stress exactly is proposed by taking into account a thermal spray process. This numerical model is a layer-buildup model based on a shear-lag theory, and the residual stress contribution comes from two kinds of the following stress components: (1) quenching stress, which was generated in molten spray particles impinged onto the substrate, and (2) thermal stress, which was generated due to differences in thermal expansion between the deposited particle and the underlying substrate. It is shown herein that residual stress predicted by the proposed numerical model coincided with the experimental one obtained by the strain gage technique, with a good level of accuracy.

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The effects of crystal orientation (θ) on the structural strength of single crystal turbine vanes and blades calculated with the finite element method (FEM) are discussed in this paper. TMS-75, a 3^rd generation single-crystal Ni-base superalloy, is chosen as the model material for turbine vanes and blades. It became clear that, (1) the elastic constant matrix changes were equivalence for each of three coordinate due to the orientation variation (0° < θ < 90°), and the strength of the turbine vane and blade were strongly related to θ, and also depended on the load and model shape. (2) The strength dependence of the turbine vane on the crystal orientation was depended on coordinate plane: there are lower Mises stress in XY plane and maximum Mises stress in near the θ=45° at both YZ and ZX Planes. (3) In the case of a blade, the influence is similar to the vane on blade tip, but the converse holds for the blade root. It is clear that the creep rupture time can be extended, when the <100> crystallographic axes is the Y or X axis of the blade under higher rotation speed.

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The effects of 125°C holding time on static strength of package solder balls and the impact strength of package solder balls have been investigated for the BGA-IC package with Pb-free solder or Pb solder. Solder ball failure can be divided into ductile failure of solder balls and interface failure between a copper and inter-metallic compound. Results show that aging time increases the ductile strength of solder balls in a package and decreases the interface strength of the package. The impact strength of solder balls in a BGA package can be predicted from the static strength of the solder balls. The predicted impact strength of solder balls was compared with the actual impact strength of solder balls. It shows a good correlation.

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The bending strength and surface strength of thin silicon devices and structural optimization of the curved image sensor were investigated in order to achieve high quality and thin camera module with high reliability. A new surface strength test method was proposed and the effects of the stress relief treatment method, the dicing method and the thickness on the bending and surface strength were clarified through experiments. A three-dimensional large deformation finite element method (FEM) analysis was carried out to obtain the stress generated when curving the image sensor. It was made clear, judging from the measured and analyzed strength of the curved image sensor, that there were three failures modes caused by 1) bending stress at the periphery of the device, 2) surface stress at the center of the device and 3) buckling due to compressive stress at the periphery of the device. Structural optimization of the curved image sensor was carried out by the newly developed genetic algorithm and the information integration method. The optimum solution of the thickness of 51 μm, a curving radius of 20 mm, and a fracture rate of 2% was obtained for a high resolution image sensor.

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