Grain growth process of polycrystalline metals which comprises of grain boundary migration and rotation of crystal orientation has been clarified by employing Phase Field Method. The strain energy stored due to the plastic deformation of polycrystal is evaluated by the crystal plasticity theory and approximately introduced to the free energy. The effects of such factors as strain energy, misorientation between grains, and curvature of grain boundary on the grain growth process have been clarified. The large misorientation between grains causes dominant migration of grain boundary, while the small misorientation causes dominant rotation of crystal orientation. The larger the magnitude of strain energy yields the faster grain growth. The changing rate of the area of grain boundary is preserved during the grain growth process. The rate of grain boundary migration depends on misorientation, and is proportional to the curvature of grain boundary.

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Macro-scale anisotropic mechanical behavior of polycrystalline meals is characterized by incorporating the micro-scale constitutive model of single crystal plasticity into the two-scale modeling based on the mathematical homogenization theory. The two-scale simulations are conducted to characterize the macro-scale anisotropy induced by micro-scale plastic deformation of the polycrystalline aggreagate. In the simulations, the micro-scale representative volume element of a polycrystalline aggregate is uniformly loaded in one direction, unloaded to macroscopially zero stress in a certain stage of deformation and then re-loaded in the different directions. Then the effect of the intergranular and intragranular behaviors are examined by several ways of illustrations of plastic deformation process. In particular, we are concerned with the concentrations of accumulated plastic strain and effective stress in the neighborhood of grain boundaries. In addition, the principal slip directions in each loading state are shown to examine the effect of self and latent hardenig on the deformation-induced anisotropy.

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The information of impact force acting on composite structures is useful in assessment of their integrity. In this paper, an identification method of impact force acting on CFRP plates is presented. First, a relationship between a force history and the induced strain responses is formulated based on the finite element method. For identifying force location, two methods are presented in this paper. The first method uses an optimization procedure with a reciprocal relationship of strain responses. In the second method, minimizing an error between measured strain responses and analytical ones gives a true force location. The force history identification can be achieved by solving an inverse problem where a penalty on the force history is imposed. Finally, the present method is verified through numerical simulations using CFRP laminated square plates with embedded PZT piezoelectric sensors. According to the results of impact force identification, the validity of the present method is verified.

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The composite materials have been expanding their application field in aircraft industries taking the advantage of their excellent mechanical properties such as high specific stiffness and strength. At present, the composite materials are come to use not only as thin plate shells but also as thicker strength members. But the failure and fracture process and property of the composites are complicated comparing with usual metallic materials. This paper presents a method to monitor some mechanical behaviors and conditions at composite joint portions using a strain sensor embedded into fastener bolt. This method enables us to grasp the information related to the structural integrity at joint portions online. In this report, the basic principles of the measurement system are shown by numerical calculations for elementary models.

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In this paper, a new method of estimating welding residual stresses nondestructively is presented. From the strain changes on the surface due to the local change of Young modulus, distributions of eigenstrain are determined by the inverse analysis. Residual stresses are then evaluated by the elastic FEM analysis by using the eigenstrain as initial condition. Since the local change of Young modulus are due to temperature dependency by heating, we refered to the method as heating method. The method is used to estimate the residual stress distribution in a plate formed by joining two sections with a butt weld. The results show that the proposed method is robust, efficient and accurate. In this procedure, the simulated measured strains are generated by adding random error to the strain response form the solution of the direct solution, and the singular value decomposition method is used as a regularization method. The effects of number of sensors and their locations, the magnitude of measurement errors on the accuracy of estimations are investigated.

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This paper is concerned with the numerical treatment of one-spatial dimensional generalized piezothermoelastic wave propagations in piezoelectric plates subjected to thermo-electro-mechanical loadings. The governing equations are based on the coupled generalized theory of piezothermoelectricity along with the modified Fourier law. The governing equations are expressed by a set of first-order partial differential equations with particle velocity, stress, electric field intensity, heat flux and temperature as the unknown variables. The solutions are obtained numerically by the method of characteristics. The numerical calculations are carried out for PZT-4 and non-piezoelectric plates subjected to ramp-type surface heating and internal heat generation by the laser-pulse heating.

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The effects of scatter in bolt preloads of pipe flange connections with gaskets subjected to internal pressure are examined. The scatter in the bolt preloads tightened by a torque wrench was measured in the experiments. The contact gasket stress distributions at the interfaces of the pipe flange connections with the gaskets were calculated under the measured bolt preloads using elastoplastic finite element method (FEM) taking into account hysteresis and non-linearity in the stress-strain curves of the gaskets. The effects of the scatter in the bolt preloads on the gas leakage were also exmained using actual pipe flange connections. As the result a difference in an amount of measured gas leakage was found to be substantial between our study and PVRC (ASME) procedure. By using the calculated contact gasket stress distributions in the connections under the internal pressure and the results of the leakage tests, the sealing performance was evaluated. The effect of the scatter in the bolt preloads is found to be substantial on the leakage. It is found that the sealing performance is worse in the actual pipe flange connection than that evaluated by PVRC procedure. The tightening efficiency was proposed taking account the leakage due to the scatter in bolt preloads.

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This paper is concerned with an axial compressive experiment on carbon steel thin-walled square pipes with a square or rectangular hole in a short column range, supported with spherical seats. Consideration has been given to an empirical formula which is the combination of the analysis based on the energy method with the experimental result. The measurement reveals that this diagram is in good design data and is agreement with those obtained experimentally for a short column range. It was found that the buckling stress decreased as the opening ratio and the opening shape ratio increased. Breaking of these carbon steel square pipes occurred as the local buckling of the flat wall with a hole.

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Fatigue and fractures such as blades and discs, which originate in the centrifugal force caused in the rotor, become factors that often cause serious accidents. The enlargement of machine and structure improves the possibility that do the latency of minute cracks and inclusions in materials in manufacturing processes. Severe working conditions also promote the propagation of the crack while operating. Thus, it is very important for the improvement in the safety of materials to analyze the interference problem of inclusion and crack. In this study, an inclusion in the rotating disc and the interference problem of the crack were examined. The influence of the mechanical property of the inclusion and the distance to the crack tip was examined. The stress intensity factor was determined by using photoelasticity and the method of caustics. As a result, the stress intensity factor was decreased when Young's modulus of inclusion increased. Moreover, the stress intensity factor decreased as the distance from the crack tip to the inclusion boundary became longer. The stress intensity factor of the crack on the rotation center side increased more than the cracks on the circumference side of the inclusion.

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Recently, coating materials are widely used in the several fields. However, it is being taken up as a serious problem that the large-scale destruction of the structure will be occurred at the time when the damage of the coating film generates. In the previous report, the basic study on the efficiency of actively restoring the bending damage of the film by adopting the concept called smart material or smart structure was proposed, and the effectiveness was shown. However, the problems of improvement on the reactivity of the actuator and application of the flexible processor function were pointed out. In this paper, the smart structure body is reported that is constituted by the information from the added strain gauge as the sensor function and the applied neural network as the processor function. As the result, it was showed that the problems of the previous report could be improved.

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This paper describes the fatigue behaviour of high V-Cr-Ni cast irons with different micro-structures. Rotary bending fatigue tests have been performed using smooth specimens in laboratory air at ambient temperature in order to understand the role of microstructural variables in fatigue behaviour. The microstructure of the cast irons consisted of austenitic matrix microstructure, lamellar microstructure consisting of austenitic microstructure and V and Cr carbides, and isolated vanadium carbides (VC) dispersed within them. Although the area fraction of VC increased with increasing the amount of V and C addition, its dependence of fatigue strength was not observed. Instead, there existed a good correlation between fatigue limit and the constituent phases of the microstructure. Fatigue limit increased as the area fraction of the lamellar microstructure increased or the area fraction of the matrix microstructure decreased, indicating that the area fraction of lamellar microstructure was a most important microstructural variable controlling fatigue strength. Fatigue crack initiation was often related to VC, but dispersed VC was a microstructural parameter of secondary importance.

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In order to investigate the effect of stress concentration on high cycle fatigue strength of austenitic stainless with corrosion pits, rotating bending fatigue tests were carried out. In this study, two types of austenitic stainless steels were used. One is Type 316 NG which is using for nuclear power generation plant and another one is Type 304 TP which is using as a pipe of industrial plants. The fatigue tests were carried out using the notch specimen which has some artificial corrosion pits on the center part of the specimens. The fatigue strength at 10⁸ cycle of specimen having some artificial corrosion pits was much lower than that of specimen without pits and all fatigue cracks were generated from the pits. To evaluate the fatigue crack initiation property from the pits, stress concentration factor was estimated by its depth and its diameter which were measured using optical microscope. As that results, the values of stress concentration factor of pits were about estimated as values from 1.5 to 2.2. The fatigue crack initiation property from pits was explained by treating a stress concentration factor as fatigue strength reduction factor.

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Fatigue tests under two-step variable amplitude loading were conducted on a high carbon chromium steel, JIS SUJ 2, in order to clarify the crack initiation lives and the intrinsic fatigue limit in subsurface fracture. Particular attention was paid to the granular area around the non-metallic inclusion in fish-eye. The granular area does not appear in short life region at high stress levels, but appears in long life region at low stress levels. Using this property, low-high sequences with a different cycle ratio at low stress level were applied to shot-peened specimens. If the granular area is observed after testing, then it is assumed that the granular area is generated in the cycle ratio examined. It was found that subsurface crack nucleation took place at the early stage of fatigue life, i.e. 5% or so. Similar low-high sequence tests with 5×10⁸cycles and 10⁹cycles at low stress levels were performed. Provided that the granular area is not observed after testing, the low stress level applied could be an intrinsic fatigue limit for subsurface fracture. After testing for 5 x 10⁸ cycles, the granular area was observed at a low stress level of 800 MPa, but not at 750 MPa. After 10⁹cycles, the granular area was not seen at 650 MPa, but seen at 700 MPa. Therefore, it is concluded that the intrinsic fatigue limit would exist around 650 MPa in the present material.

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The effect on the low-temperature plasma treatment of PBO fiber and the interfacial strength properties between PBO fiber and epoxy resin was investigated. PBO fiber was modified by oxygen plasma treatment. The monofilament tensile test was carried out to investigate the existence of influence on the PBO fiber strength. The microdroplet test was performed to measure the interfacial shear strength. It was found from the experiments that the tensile strength of PBO fiber modified by plasma treatment was decreasing slightly in all the test specimens because the damage by the etching was confined to the skin layer. The interfacial shear strength between PBO fiber and epoxy resin was increased about 38.4% in comparison with non-treated PBO fiber. It became clear that it was because the carbonyl group and carboxyl group were introduced on the surface of PBO fiber from the result of XPS analysis.

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A temperature-insensitive damage evaluation parameter for composite laminates is proposed. Ultrasonic wave velocity is directly related to material stiffness, so that it is a quantitative parameter that gives information about the mechanical state of the material. However, ultrasonic velocities vary with temperature therefore environmental factors might cause non-negligible error in inspected results. In this work, the angular dependence of Lamb wave propagation, i.e., the acoustic anisotropy, is exclusively focused on and the change in the acoustic anisotropy is used as a damage evaluation parameter. It is experimentally confirmed that the acoustic anisotropy is significantly altered by matrix cracks formation although it is insensitive to temperature variation. It is also shown that the combination of different Lamb modes is a more promising method for predicting the effective stiffness of damaged laminates.

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Carbon fiber/epoxy unidirectional laminates exhibit low flexural strength in contrast to their high tensile strength. This is because the flexural failure is dominated by fiber microbuckling at the compression side during bending. For the same reason, the Charpy impact properties cannot be improved only by increasing the tensile strength of the fibers. This paper examined the effect of hybridization on the flexural impact properties of a PAN-based carbon fiber/epoxy unidirectional laminate strengthened with pitch-based, low modulus carbon fibers. PAN-based carbon fiber layers, with fiber modulus of 230 GPa, were used as the core, which was sandwiched by thin outer layers of pitch-based carbon fibers with a lower modulus of 55-155 GPa and a larger compressive failure strain than the PAN-based fibers. An instrumented Charpy impact test showed that the hybrid laminates had higher energy absorption than the monolithic PAN-based laminate. SEM fractographs indicated that the ratio of the tensile failure region in the failed surface increased with the increase in the content of pitch-based low modulus fibers in the hybrid laminates, from 20 percent in the monolithic PAN-based fiber laminate to a maximum of 54 percent in the hybrid laminates. The increased tensile failure region, with suppressed compressive failure, resulted in the higher impact performance of the hybrid laminates. The large compressive failure strain of the pitch-based low modulus fibers was inferred to have the effect of restraining fiber microbuckling at the compression side and improving the impact resistance of the PAN-based fiber composites.

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