The mechanical strength properties of ceramic/metal substrates exposed to cyclic thermal loadings were studied in order to discuss the effects of the number of thermal loadings on the residual strength of the substrates. First, thermal stress analysis was performed using the finite element method for an examination of the thermal stress behaviors during the cyclic thermal loading processes. Next, test samples of Cu/AIN substrates, including brazing filler metals of AgCuTi, were prepared by brazing in a vacuum furnace. Thirdly, thermal cycling tests with cycle numbers of 25,50 and 100 were conducted on the test samples. Finally, four-point bending tests were conducted on the thermally-loaded samples to evaluate residual strength. The results showed that residual strength increased after 25 thermal cycles. In contrast, thermal cycling with 25-100 cycles resulted in a reduction of residual strength. These behaviors were discussed in terms of residual stress relaxation and a mechanism for the microscopic damage of sintered materials with polycrystalline structures.

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Experiments on crack initiation and propagation along the Cu/Si interface in multilayered films (Si/Cu/SiN) with different thicknesses of the Cu layer (20 and 200 nm) have been conducted by using a nano-cantilever and millimeter-sized four-point bend specimens. To examine the applicability of cohesive zone model (CZM) criterion for interfacial delamination along the Cu/Si interface in nanoscale stress concentration, an exponential type of CZM is utilized to simulate the observed delamination processes using the finite element method. After the CZM parameters for the Cu/Si interface are calibrated by an experiment, interface cracking in other experiments is predicted with obtained CZM parameters. This indicates that the CZM criterion is universally applicable for describing cracking along the interface regardless of specimen dimensions and film thickness which include the differences in plastic behavior and residual stress. The CZM criterion can also predict interfacial cracking along Cu/Si interfaces with different stress singularities.

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In this study, the enriched finite element method is applied to compute the intensity of singularity for dissimilar material joints with 2-real singularities. Different mesh types and different size of the enriched region are applied to improve an accuracy of the results. It is shown that the results from applied the enriched FEM to the 3-material junction is agreed with those using a conventional FEM. In addition, numerical error is reduced by changing mesh types from linear to quadratic elements.

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We have developed an evaluating method of plastic Poisson's ratio as a function of equivalent plastic strain (PS) for polymer materials. The PS is used to simulate permanent volumetric deformation due to void extension and plays an important role in simulating mechanical properties of crazing behavior which appears in uniaxial or biaxial tension state. Unfortunately stress-strain relation (SS) strongly depends on PS, which makes the evaluations of PS and SS data difficult. In this paper we have proposed a self-consistent equation of true stress for uniaxial / biaxial stress state. We can successfully separate the evaluations of PS and SS by introducing the equation into the processes, and the problem has been solved. Hence this method enables us to build an application that automatically evaluates PS and SS with some optimization techniques such as GA.

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A rapidly bifurcating crack in PMMA is photographed by high-speed holographic microscopy at about 5 s after bifurcation. Crack speed is 612m/s. Crack opening displacement, COD, is measured along two branch cracks as well as the mother crack. The COD of the mother crack is approximately proportional to the square root of the distance r from the crack tip. The COD of one of the two branch cracks is roughly proportional to √r, but not about the other branch crack. This is thought to be caused by the three-dimensional structure of the branch crack. Stress intensity factors and energy release rates of each of the two branch cracks are obtained from the CODs of the two branch cracks. Stress intensity factor and energy release rate of the whole bifurcated crack are obtained from the COD of the mother crack. The energy release rate of one of the two branch crack is about half of the entire energy release rate of the bifurcated crack.

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Crack opening displacement, COD, and stress intensity factor, K_I, of bifurcated cracks are studied experimentally, and are compared with theoretical prediction based on the linear elastic fracture mechanics. The COD of the mother crack and the COD of two branch cracks of a bifurcated crack are measured by Moire interferometry. The COD of the mother crack gives the stress intensity factor, K_IM, that relates to the total energy release rate of the bifurcated crack. On the other hand, the COD of a branch crack gives the stress intensity factor, K_IB, of the branch crack of the bifurcated crack, which K_IB relates to the energy release rate of each branch crack. The measurements say that the value of K_IB approaches to 1/√2 times as large as K_IM in the vicinity of the tips of the branch cracks. This experimental result is in agreement with the theoretical prediction based on the linear elastic fracture mechanics.

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Since majority of phenomena which occur around us are coupled ones, the necessity for coupled analysis is well-known. In many computational mechanics studies, however, the coupled effect is disregarded because of the difficulty to consider it in a numerical computation. In other words, the coupled analyses are much complicated as compared with the non-coupled ones. We have employed the EFMM for this class of problems as this method has various advantages, for example, analysis accuracy improves sharply as compared with the FEM. In the present paper, we aim at conducting efficient coupled analysis, which does not use a middle-point node by using the present method.

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