Photoelasticity is a non-contact and full-field type method of experimental stress analysis. It does not provide individual stress components directly. In this study, a new technique of stress separation is developed, in which this problem is divided into the following three: (1) determination of the difference of the principle stresses based on isochromatic data, (2) estimation of unknown boundary values from the difference of the principal stresses, and (3) computation of individual stress components inside the body based on the estimated boundary values. Problem (1) is solved by using the isochromatic fringe images obtained at incremental loading steps. Fourier transform method and direct method are applied to determine the difference of the principal stresses. Problems (2) and (3) are formulated and solved by BEM. A nonlinear optimization method is employed to solve problem (2) since the relation between the unknown boundary value and the difference of the principal stresses is nonlinear. The effectiveness of this technique is verified through numerical simulation and experimental data analysis.

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New hybrid and parallel genetic algorithms, GAs, are proposed in this paper in order to improve the convergence of structural optimization. A fully stressed design method, FSD, and a GA were incorporated in the hybrid GA. In the parallel GA, the 'island model' was applied to reduce computing time. Stress analyses were carried out with a commercial FEM code to obtain the optimum solution with high reliability even in a complex model. As a result of the axi-symmetric shell model, the optimum solution by using the proposed hybrid GA was 50% lighter than that by using the simple GA. Furthermore, the computing time using the parallel GA with 10 processors was reduced by up to 1/7 of that with one processor. These methods were used to optimize the thickness of the 3-dimensional shell model of a CRT. As a result, the weight of the optimum model was 25% lighter than that of the reference model.

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In this paper a boundary integral equation method is developed for the analysis of the large deflections of a shallow arch. The formulation employs the fundamental solution of the beamcolumn problem and this approach creates not only boundary integrals but also domain integrals as well owing to the presence of nonlinear term. This domain integral terms are evaluated as 'external force' and resultant algebraic equations for boundary values are solved by iteration method. Successive equilibrium paths corresponding to each loading are traced by arc-length method. Some numerical examples are presented to show the usefulness of the present method.

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This paper describes a hexahedral mesh generation technique for a geometric model's shape changes, using a pre-change model's mesh. First this system compares a pre-change geometric model with a post-change geometric model. The changing section obtained in the comparison is used to generate a new mesh. The system then generates a hexahedral mesh of a post-change model automatically by combining the mesh of a pre-change model with the mesh of the changing section. The advantages of this technique are (1) a hexahedral mesh with the same high quality as the a pre-change model's mesh can be generated and (2) the time required for generating hexahedral meshes can be decreased by about 80 percent compared with the conventional method.

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Recently, meshless method, which needs nodal data only as input data, is widely noticed of its significance. The authors have recently applied one of meshless methods, Free Mesh Method (abbreviatred hereafter by FMM), to the elastic-plastic large deformation problem. FMM proposed by Yagawa et al. has some similarities to the conventional FEM, where the tentative triangular element are created around the node. This paper describes the formulation and implementation for FMM in parallel computational environment using PVM (Parallel Virtual Machine) communication architecture designed for PC clusters. Funthermore, FMM can utilizes the remesh algorithm, since FMM is based on Node-by-Node concept. The present paper will confirm effects of remeshing algorithm to improve accuracy of numerical solutions as an example of largely deformed shear block.

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This paper presents a numerical solution to boundary shape optimization problems taking into account material non-linearity. The goal aimed in this paper is to minimize external work by varying a boundary shape under a volume constraint. Shape variation is described by using a one-parameter family of mappings defined in a domain where a continuum lies initially. The shape sensitivity is derived using the Lagrange multiplier method and the formula of the material derivative. A procedure to solve this problem using the traction method is presented, which one of the authors has proposed as an approach to solving domain optimization problems. The varidity of proposed method is verified by applying basic numerical examples and by comparing with results considering only linearity.

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The influence of artificial inclusions on tensile properties of iron-base sintered material with artificial inclusion is sudied experimentally and numerically. Stress and strain around inclusion have been examined by FEM. The microscopic observation of the initiation and growth of voids leading to macroscopic necking and subsequent ductile fracture has been carried out. The ultimate tensile strength depends on the interparticle spacing;which is function of volume fraction and particle size of inclusion. Initiation of a void at the interface between matrix and inclusion depends on the sort and size of inclusion. The onset of numerically predicted microscopic necking, internal necking, prior to the experimentally observed macrosoopic necking relates to the distance between inclusions which is depend on both of the volume fraction and grain size of inclusion.

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The mechanism of the occurrence of longitudinal surface cracks near slab corner has been investigated based on both the thermal stress analysis of solidifying shell in the continuous casting mold and experimental consideration. In the stress model, the coupling between thermal deformation of the shell and temperature distribution in the mold wall was taken into account. It is cleared that the conventional constant-tapered mold is insufficient to prevent the cracks. By applying a newly developed variable multi-tapered mold which was designed from the stress analysis, the high speed castings of 5 m/min have been put into practice without corner cracks.

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Elastic-plastic stress analysis of cracked fiber-reinforced plastic (FRP) was conducted by the finite element method. The inhomogeneous FRP was modeled as a two-dimensional laminated structure composed of elastic-perfectly plastic matrix material, orthotropic elastic fiber and homogeneous FRP. The size of the plastic zone near the tip of a mode II matrix crack was determined for an inhomogeneous composite and an unreinforced matrix material. Under the same value of the matrix stress intensity factor, K_IIm the length and the height of the crack-tip plastic zone obtained for an inhomogeneous composite are equal to those obtained for an unreinforced matrix material in the range of K_IIm≤0.2σ_Y√(πd_m) where σ_Y is the yield stress of the matrix material and d_m is the height of the matrix phase in the inhomogeneous FRP. On the other hand, for large K_IIm value, the plastic zone length obtained for an inhomogeneous FRP is larger than that for an unreinforced matrix material, but the plastic zone height is smaller. A simple method is proposed to estimate the length and the height of the plastic zone ahead of the tip of a mode II crack from the elastic stress distribution in the inhomogeneous FRP.

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The propagation path of cracks in continuous fiber-reinforced plastics (FRP) under remote mode I loading was studied. Two FRP models are used in the two-dimensional boundary element analysis:the inhomogeneous FRP model which has a laminated structure composed of matrix and fiber, and the three-layered FRP model in which a thin matrix layer is sandwiched between homogenized FRP plates. The matrix stress intensity factors and the non-singular T-stress, T_m, were calculated for a crack parallel to the fiber direction in a matrix layer of these models. When the residual stress in the matrix layer is negligible, T_m is negative for typical FRP composites. For long cracks, the absolute value of T_m for the inhomogeneous FRP model is larger than that for the three-layered FRP model, and the ratio of these values is independent of fiber properties. A crack is predicted to propagate along the centerline of the matrix layer of FRP composites without the matrix residual stress because of a negative T_m value and the sign of the mode II matrix stress intensity factor. The effects of the residual stress, the height of the cracked matrix layer, and the crack length on the crack propagation path were discussed on the basis of the results of the present analysis.

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The purpose of this study is to investigate the effect of morphology on the tensile properties and fracture properties of PC/ABS polymer alloy. From TEM observation the co-continuous phase structure is formed in PC/ABS (60/40) . PC and ABS form continuous and dispersed phase in PC/ABS (80/20), respectively. The yield stress, Possion's ratio and tensile strength follow the law of mixture. The Young's modulus in co-continuous morphology appears the maximum value. Wihle, the crack growth (extension) resistance in PC/ABS (80/20) is more excellent than other morphologies. On this samples, SEM observation shows pulling ABS dispersed phase out of the fractured surface. Furthermore, TEM observation appears that the boundaries of rubber particles underneath the fractured surface have irregular and jagged shape. The reason of its higher crack extension resistance, consequently, is the multiplied effect of release of tri-axial stress and energy consumption of damaged rubber particles.

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Fatigue crack growth test under constant amplitude loading was conducted on a grain-oriented 3% silicon iron using servo-hydraulic fatigue loading system. The configuration of specimen surface around fatigue crack tip was transferred to a thin replica film and examined by means of an atomic force microscope (AFM). Discrete slip lines which emanated from crack edges were observed clearly along the two preferred slip directions (±55°). It implies that two preferential slips operated to almost identical extent simultaneously and fatigue crack grew in mode I. The slip deformation during loading and unloading was observed successively and it was found that the operation of slips behind the fatigue crack tip resulted in crack closure and that at the crack tip brought about crack growth. The serface displacement during one cycle was measured quantitatively by using image processing technique. The pattern of the relationship between load and slip deformation was correlated well with that between load and crack tip opening displacement, CTOD, and the slipping distance near the crack tip corresponded to the ideal CTOD.

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The propagation behavior of small fatigue cracks was numerically simulated to evaluate the development of crack closure with crack growth. The effect of the interaction between crack-tip slip band and grain boundaries on plasticity-induced crack closure was analyzed under plane stress condition. The crack and slip bands were assumed to be coplanar. When the slip band crosses the grain boundary, the larger resistance of slip motion in the next grain induces a reduction in the crack opening displacement range and an increase in the crack opening stress. The distribution of the residual stretch was geometrically similar to the change of the maximum crack tip opening displacement with crack extension. The relation between the crack opening displacement range and the effective stress intensity range was nearly unique. When the slip band extends over many grains, the irregularity of crack opening displacement range and crack opening stress diminishes. The crack propagation life can be calculated as a function of the crack length and the stress level on the basis of the crack-tip opening displacement range.

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It is well known that the shot peening process is often used industrially for the purpose of improvement of the fatigue strength of many kinds of steels. Generally the surface of these steels subjected to this process is hardened and addition to it, the compressive residual stress is also induced on the surface layer. In this study, the fatigue tests of shot-peened steel SUS 304 were conducted using the rotating-bending fatigue test machine, and residual stresses were detected by X-ray stress measurement. And surface characteristics related to residual stress σ_R, hardness and microstructure are also investigated to clarify the influential factors on the bending fatigue strength of stainless steel SUS 304 by shot peening. As a result, the surface layer was hardened by the shot peening process and the strain-induced transformation was ascertained by X-ray analysis. And residual stresses were almost released at the initial time during fatigue cycles. Concerned about work hardening, it is also studied precisely. We found that the increments of hardness was attributed to both martensitic transformation and hardness of austenite itself, and then the bending fatigue strength of austenitic stainless steel with shot peening process was improved by twenty percents. Consequently, it is found that the increments of hardness by the shot peening are mainly due to hardness of austenite structure itself, and it affects the improvement of the fatigue strength of the shot peened austenite stainless steel.

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Thermal barrier coating process has been established in gas turbine and was used for some parts operating at elevated temperature. Thermal barrier coating was constructed with ceramics layer and bond layer as MCrAlY alloy (where M is Ni, Co or Fe). The mechanical properties such as ductility of CoNiCrAlY alloy change drastically with temperature. Then it is important to clarify the influence of temperature on low-cycle fatigue property of thermal barrier coated material. Low-cycle fatigue tests of thermal-barrier coated Ni-base superalloy were performed at room temperature, 773 K, 973 K and 1 088 K. From the experimental results, decrease in fatigue life of the thermal-barrier coated Ni-base superalloy was observed at room temperature as compared with that of the uncoated one. On the other hand, fatigue life of the coated one was increased as compared with that of the uncoated one at 1 088K. Difference in fatigue life between coated and uncoated material was explained by a crack initiation behavior, which was obtained by A. C. potential method and observation by optical microscope. The number of cycles to crack initiation of coated specimen is smaller than that of uncoated one at room temperature. On the other hand, crack initiation life of coated specimen is larger than that of uncoated one. If was discussed from the experimental results that crack initiation and fatigue life were affected by the ductility of the bond layer.

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As a series of studies to clarity the mechanism of crack initiation and propagation in rolling contact fatigue, the experimental method of caustics has been applied to disk-to-disk rolling contact fatigue tests. The cusp-like and round type caustic images were generated from the rolling contact point and the crack tip, respectively. Although the shape and size of the cusp-like image depending on the magnitude of applied load was constant, that of the round image was markedly changed with the relative position between the crack and the rolling contact point. The experimental caustic images have been simulated using a computer program developed by combining the theory of caustics with the theory of boundary element method. By comparing experimental caustic images with simulated ones, it is shown that the round type caustic image obtained in rolling contact is strongly affected by shear deformation of the crack.

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Dynamic fracture of PMMA was studied using a Cranz-Schardin high-speed camera. The single-edge-notched specimen was pin-loaded with special fixtures so that it could split and fly away after the fracture. The flying velocity was measured to estimate the elastic energy stored in the specimen. The nonelastic energy was also estimated from the visco-plastic deformation. The fracture energy was evaluated and correlated with the external work applied to the specimen.

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In this work, stress concentration factors (SCFs) K_t of a flat bar with double circular-arc notches or double V-shaped notches are considered on the basis of exact solutions new available for special cases and accurate numerical results. First, for the limitting cases of deep and shallow notches, the body force method is used to calculate the SCFs;then the formulas are obtained as K_td and K_ts. On the one hand, upon comparison of K_t and K_td it is found that K_t is nearly equal to K_td if the notch is deep or blunt. On the other hand, if the notch is sharp or shallow, K_t is mainly controlled by K_ts and the notch depth. The notch shape is classified into several groups according to the notch radius and depth;then, the least squares method is applied for calculation of K_t/K_td and K_t/K_ts. Finally, a set of convenient formulas useful for any shape of notch in a flat test specimen are proposed. The formulas yield SCFs with less than 1% error for any shape of notch.

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In this paper, the singular stress field around the edge point in a bonded strip subjected to thermal loading is analyzed by body force method. Based on the numerical results, the effect of the beam geometry and material combination on the stress intensity factors are investigated. It is found that the singular stress σ_θ caused by heating or cooling may be positive or negative, depending on material combinations. It is also found that there is not a unique relationship between the stress singularity factor K and the eigenvalue λ.

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Thermal distortion of a large deployable reflector, for use on board a satellite, was evaluated using an artificial environmental chamber. The large deployable reflector, which is 15 m in diameters, was developed based on a modular concept in which the structure consists of several basic modules about 5 m in diameter. Each basic module consists of a mesh surface, a cable network, and a truss structure. The mesh used for the reflector surface reduces the weight, and the cable network is formed so that the mesh surface is parabolic in shape. The truss structure maintains the length of cable and the form of the mesh surface.

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Cold upsetting of a circular cylinder is often used to evaluate the cold forgeability of metals. The index of the forgeability is the critical strain where a crack occurs on the expanding free surface of the upsetting cylinder. At the onset of surface cracking circumferential strain and compressive axial strain are represented with a linear relation having the gradient of about 0.5. On the other hand Kuhn⁽9) performed the upsetting of cylinders with a modified shape, and showed experimentally that the gradient of the linear relation was higher than 0.5. The modified shapes of a specimen are artificially pre-barreled by machining a taper or a flange on the cylinder. The purpose of the present investigation is to make the difference of the gradient clear between normal and modified specimens using numerical simulation. Occurrence of cracking is associated with the multiplicity of solution from a view point of the mechanics of plasiticity. In general, it would be believed that the multiplicity corresponds to plastic instability. But plastic instability does not necessarily cover all of the multiplicity, but load instability must be taken into consideration. To the evaluation of cracking in upsetting the criterion of load instability can be applied from the reason that co-existence of plastic and neutral solutions is possible at load instability. The mode of cracking must be consistent with deformation required on elasto-plastic boundary, and only two kinds of mode (mode P and O) are permitted. For cylinders with the modified shape only mode P is predicted. The predicted linear relation of critical strains in simulation is found to be in very good agreement with the relation of cracking obtained expermentally.

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The indentation crack length approach was adopted and further elaborated to evaluate residual stress and toughness of the brittle coatings:two kinds of glass coatings on steel. The influence of the residual stress on indentation cracking was examined in as-received coating condition and by in-situ superimposing a counteracting tensile stress. For purpose of providing reference toughness values stress-free pieces of separated coating material have also been examined. Thus results of the two complementary sets of experiments were assumed to prove self-consistently toughness and residual stress data of the coating. In particular, the in-situ bending of specimen in combination with the indentation test allowed us to vary deliberately the residual stress situation in glass coating. Thus experiments which utilized the combination of bending test and micro-indentation were introduced as a method to provide unambiguous information about residual compressive stress. Toughness and residual compressive stress of glass coatings used in this study were 0.46∼0.50 MPa·m^1/2 and 94∼111 MPa, respectively. Furthermore, a thermoelastic calculation of the residual compressive stress was performed and it is found that the value of residual compressive stress at coating surface of specimen was 90∼102 MPa.

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Measurements of inherent strain generated in a butt joint and a bead on plate have been made by the sequential removal of layers. It is shown from experiments that the distribution of inherent strain in a bead on plate is almost the same as one in a butt joint. The rise of average temperature, which is derived from similar law of themal conductivity and is calculated from welding coditions and plate sizes, isuseful for arranging the distribution of inherent strain. The plate length does not affect the distribution of inherent strain on the center plane of plate length, when the plate length is above one and half times as long as the width of welded plate.

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Mechanical performance of artificial hip joints has been improved by basic researches on various fields, but there are some cases where a reoperation is required within a few years. The inappropriate position of the installed socket is considered as a cause of reoperation. Appropriate installing of socket makes enough amount of contact area between the socket and the pelvis, so that the hip joint stays stably. Actually, the socket position is decided by means of a careful examination on medical scene. But there are hardly mechanical and numerical examinations, the surgeon's experience weighs heavily in the decision of socket position. We propose SSM (Swelling Sphere Method) to search an appropriate socket position based on the area. In order to evaluate effectiveness of SSM, first, we compared it with a general optimization method. Next, the SSM was applied to obtain the appropriate socket position for a geometric model of pelvis constructed from a series of CT photographs of a patient. Further, by using a finite element analysis, we found that the socket position has an equal aptitude to surgeon's decision from the mechanical point of view.

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