Ni-NiO composites with different NiO contents were fabricated by a conventional PM method. Nickel oxide particles, which were selected as dispersoids, were embedded in nickel matrix. Tensile tests were conducted on the composites containing up to 9 weight percent of NiO at room temperature. Typical tensile properties, such as yield strength, tensile strength and elongation, of the composites were evaluated. Yield stress of the composites monotonically increased with increase of the NiO content. In contrast, both tensile strength and elongation decreased with increasing NiO content. Variations in the tensile strength of the composites were explained on the basis of the nature and amount of dispersoids and their interaction with nickel matrix. The decrease in the tensile strength was related to its density change. In addition, the relationship between tensile strength and NiO content was well described by Eudier's equation. Decreases in both tensile strength and elongation were caused by propagation of grain boundary cracks initiated from decohesion of dispersoid/matrix interface.

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Computational prediction of load carrying capacity of notched [90/+45/-45/0] ns CFRP laminates is made to verify the method proposed previously by the authors. In the damage developed ahead of the notch tip of laminates, load is supported by the delaminated laminas which can be regarded as bridging fiber bundles. In the method, the damage is simplified to a fictitions crack on which fiber bundle bridging occurs, and the relationship between cohesive stress acting on the fictitious crack surface and crack opening displacement is statistically determined. It is computationally estimated that the load carrying capacity of the laminates tends to decrease with the decrease in the pull-out length of the fiber bundle. The tendency coincides with that obtained in the experiment Furthermore, the load carrying capacity is quantitatively predicted for various values of fiber volume fraction and critical stress which governs the delamination.

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In this study, a method of determining fiber orientation distribution in short fiber reinforced composites using image analysis is proposed. First, the composite is irradiated with parallel rays from several directions and then the areas of regions on planes of projection, which are exposed to the parallel rays, are measured. Using only this information, we evaluate the fiber orientation distribution. We applied this method to the determination of fiber orientation distribution of a short fiber reinforced composite. Consequently, the validity of this method is proven.

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In ductile metal particle-reinforced ceramic composites, the prevention of crack opening by the metal particles bridging the surface of the matrix crack is said to be the cause of toughening of such a composite. Since the radii of the particles in such a composite are considered to be varied, at the stage of modeling such a composite, the distribution of the radii of particles must be considered. Micromechanics is one of the powerful methods which can take the microstructure of the composite into consideration. In the present research, micromechanical analysis is performed of the metal particle-reinforced composite with crack-bridging particles of various radii, by both introducing the stereological concept to the micromechanical model and considering interfacial debonding between a particle and a matrix. The expressions of energy release rates for both a matrix crack and a debonding one, which include the terms expressed only by the probability density function of the distribution of the radii of particles, can be obtained.

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Recently integral large composite structures have been applied to many structures of vehicles because of their low cost and high reliability. However, since the structures are large and complicated, a fracture simulation system is required to assess the safety of inspected damages. In this study, the efficiency of a 2-dimensional FEM damage simulation for splitting, matrix cracking and nonlinear share deformation was examined as compared with the experimental results. To improve the analytical results, a fractal distribution model and a share bridging effect model were constructed based on the fracture micro-mechanisms of matrix cracking and splitting, and a damage simulation based on the models was developed. As a result, a simulation that considered the fracture micro-mechanism was found to be effective for damage estimation of FRP laminates.

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It is well known that ceramic matrix composites (CMC) exhibit improved fracture toughness which is necessary for heat-resistant structural ceramics. In the presence of a sharp defect, however, the CMC show nonlinear and nonelastic behavior yield many microcracks around a main crack tip. A conventional fracture toughness evaluation approach applied to many kinds of metal, therefore, cannot be directly applied to the CMC. Although several approches have been applied to the CMC, a simple approach applicable to a damage resistant design of the CMC structure has not been established. In this study, fabric SiC/SiC composites were used to evaluate the fracture toughness. Two types of specimens were tested and an evalation method of the fracture toughness was investigated experimentally. It is shown that the fracture resistance curve and the fracture toughness as a material property can be evaluated in terms of a stress intensity factor using an equivalent crack length calculated from a compliance regarding the origin of a load-deflection curve.

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In order to evaluate quantitatively the effect of inherent defects on the fatigue strength of aluminum casting alloys, a fatigue strength prediction by the √(area) parameter model was performed using the statistics of extreme values of defect size. Rotating-bending fatigue tests were carried out on AC4C aluminum alloys with three levels of defect size. It was found tha the fatigue strength decreased with increasing defect size and the prediction for the lower limits of fatigue strength of these aluminum alloys was successfully correlated with the results of experiment.

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To investigate the effect of the Si-phase on fatigue properties of Al-Si eutectic alloys in a long life fatigue range (N≤10⁷) and super long life fatigue range (N>10⁸), rotating-bending and tension-compression fatigue tests and FEM analysis were carried out. Fatigue test specimens were prepared from two materials produced by two processes: continuous casting and extrusion. The results obtained are as follows. In the case of continuous casting, all fatigue fractures were caused by shear-type cracks, resulting in shorter fatigue life. In the case of extrusion, the fatigue fracture origin in the long life fatigue range was in the Si-phase, while in the super long fatigue range it was in the matrix. The fatigue limit defined by the cycle N=10⁷ can be predicted using the √(area) parameter model, i.e. with two parameters, the maximum size of Si-phase √(area)_max and the Vickers hardness H_v of Al-marix, without the influence of the Si-phase. In the case of Al-Si alloy, a crack leading to fracture initiates even after 10⁸ cycles under very low stress. Thus, super long life fatigue behavior must be taken into account to both material and structural designs.

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Single-edge-notched specimens of a structural carbon steel and a low-alloy steel were fatigued under axial loading. The initiation and propagation behavior of short fatigue cracks emanating from a sharp notch was investigated. The resistance-curve (R-curve) method was used to predict the fatigue thresholds of notched members. The R curve was constructed in terms of the experimentally determined threshold value of the maximum stress intensity factor which was the sum of the threshold effective stress intensity range ΔK_effth and the opening stress intensity factor K_opth. The value of ΔK_effth was constant and the R curve was independent of crack length and notch geometry. The predicted values of the fatigue limit for crack initiation, the fatigue limit for fracture, and the nonpropagating crack length agreed well with the experimental results. The effect of the material property or Vickers hardness on the fatigue notch sensitivity was discussed on the basis of the R-curve method. A simplified method to determine the R curve using Vickers hardness or the tensile strength was proposed for design applications.

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Retardation behavior of fatigue crack growth due to crack surface soldering was investigated experimentally in a low-alloy steel. The flux-cored solder wires located within an initial notch were heated to above melting temperature. When a crack was opened by loading, liquid solder easily infiltrated up to the crack tip by a capillary phenomenon. By unloading subsequent to cooling to room tempeature, an artificial wedge was formed between the crack surfaces. This crack surface soldering has a preferable effect on fatigue crack growth control. When the crack-opening load during crack surface soldering is equal to the maximum load of fatigue cycling, the fatigue crack is arrested.

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The micro-mechanism of fracture in brittle material of PMMA is analysed by focusing the parabolic patterns formation process which can be observed on fractured surfaces at some crack velocity region. The initiation and extension of secondary cracks are studied by the use of a model proposed for the mechanism. The foci of parabolas which are the nuclei of the secondary cracks are examined in detail. The positions of foci from the main crack front are measured to obtain the average initiation stress. The size of the nucleus, which is defined as a smooth central part, is considered as the critical size for the unstable crack growth, from which the surface formation energy in the microscopic aspect is deduced. The parabolic patterns obtained in the simulation are in good coincidense with the observed patterns including the velocity effect on the configuration of patterns.

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Effects of a surface layer with chill structure, specimen thickness, shape of mold and powder lubrication in a sleeve on fracture mechanic characteristics were investigated for aluminum alloy die castings ADC12 with two different types of molds (flat and staircase shapes). The results are as follows. In the case of a flat mold, a decrease of thickness improves mechanical properties. A surface layer with chill structure has a substantial influence on mechanical properties, but little influence on fracture toughness. In the case of the staircase mold, the mechanical properties are the same as for the flat mold. On the other hand, the powder lubrication in the sleeve improves the fracture toughness and reduces the scatter in fracture toughness. There is little influence of both the surface layer with chill structure and the specimen orientation on the fatigue crack growth resistance, but with decrease of specimen thickness, the fatigue crack growth resistance decreases, especially in the region of near-threshold fatigue crack growth rate. In addition, the lubricating method has no effect on the fatigue crack growth resistance for the staircase-shapes die castings.

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A method is proposed for simplified nondestructive evaluation of multiple cracks by means of the d.c. potential drop technique for a subregion containing some cracks. The distribution of the potential drop for cracks, except for end cracks, in a subregion is measured and calculated by assuming values for the depths of the end cracks and by assuming arbitrary values for the depths of other cracks. The calculation is based on simplfied analysis of crack interactions. Modification of the depths of the other cracks is repeated until the difference between measured and calculated potential drops is minimized, where the depths of the end cracks are fixed. The analysis can be done in a short time using a personal computer. It is shown that the evaluated crack depth is in good agreement with the actual one.

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The caustic method is used to determine the stress intensity factor K_I. In the case of specimens with various thickness and different degrees of open notches, however, the caustic method gives an error in the evaluation of K_I. In this paper, the caustic method was studied for specimens with thicknesses from 2.0 to 7.7 mm and open notches from 0 to 90deg. for each thickness, providing 16 different combinations, under mode I loading. The results are summarized as follows. The transmitted caustic method is a useful technique to determine values of the stress intensity factor in these specimens. The conventional determination of K_I using the caustic method is valid for all of the above-mentioned combinations, when the initial curve radius γ₀ is larger than the minimum initial curve radius γ^min₀ obtained by this study. A linear relationship was found between γ^min₀ and the thicknesses for each notch opening. A method based on the distribution of three-dimensional stress field is proposed to expediently yield values of K_I using caustic method in the case of γ₀<γ^min₀.

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A solution to the second mixed boundary value problem for thin plate bending is derived under the following loading conditions: two components of the external force are applied on two parts of the boundary, and equivalent shearing forces and an angle of deflection in the y-direction are applied at the remaining two parts of the boundary which are straight. To obtain the solution, complex stress functions and a rational mapping function are used. The half-plane with surface and subsurface cracks under uniform bending moment has been considered as an example. The geometry of the body is symmetric about the crack line and is a doubly connected region. The distributions of stress and stress intensity factors are obtained and presented graphically.

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Magnetostriction curves of low-carbon steel were measured while applying a magnetic held, either parallel or perpendicular to the uniaxial applied stress. When ferromagnetic steels are magnetized, dimensional change occurs, which is called Magnetostriction. As the magnetic field strength increases, domain wall movement first occurs, causing an increase in magnetostriction, and followed by rotation of domain magnetization, which reduces magnetostriction. The magnetostriction then shows the maximum with the applied field for which the rotation of domain magnetization starts to occur. The maximum value indicates the amount of domain wall movement, which depends on the domain structure in the demagnetized state. The stress application also affects the domain structure through the magnetoelastic interaction. Considering the internal energy, it is predicted that the maximum magnetostriction parallel to the magnetic field increases when the field is either parallel to the compressive stress or perpendicular to the tensile stress. This is potentially useful for nondestructive stress measurement. In this study, the maximum magnetostriction was measured as a function of the applied stress for low-carbon steel, the result of which confirmed the above prediction.

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A technique to measure surface stress (strain) in non-magnetic material using the magnetostrictic effect of magnetic foil and film was developed. It is called the magnetic foil and film method. The foil is adhered and the film is sputtered or electroplated. In the present experiment, Ni is used. Apparent magnetic permeability μ_a of the foil and film is monitored by highly sensitive magnetic permeability meter. The measured μ_a decreases monotonically with increasing stress σ. It is concluded that the technique can be used for stress (strain) measurement in nonmagnetic materials. A rotating bending fatigue test showed also that cyclic stress causes the decrease ofμ_a of the foil. The method could also be used for cyclic stress measurement.

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This paper describes an efficient calculation method for elastoplastic analysis of three-dimensional large structures on a personal computer aided finite element method (FEM). The composition of stiffness matrix requires a long execution time on the FEM. Thus the following three methods are presented to decrease the execution time: (1) the copy process of the stiffness submatrices of congruent or similar figure element and/or block, (2) a triple-tandem-type substructuring method and (3) an improved method of (2) using both (1) and a parallel calculation process. (1) is effective for reducing the time required for elastic analysis. (2) effectively decreases the time for elastoplastic analysis. The parallel calculation process is carried out on several microcomputers, so-called transputers in order to decrease the time required for both elastic analysis and elastoplastic one. (1) and (2) are applicable to parallel calculation. (3) is the most effective method for decreasing the time for both elastic analysis and elastoplastic one. To verify the validity of (3), the FEM using (3) is applied to the elastoplastic analysis of a three-dimensional elastic structure under tension.

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We describe the calculation of mechanical properties of a solid using a molecular dynamics method. The thermal expansion coefficient and elastic constants of α-Fe are calculated using an empirical potential, that is, Johnson potential. The thermal expansion coefficient is calculated using a differential operation of the temperature dependence of the lattice constant obtained from the NPT ensemble molecular dynamics analysis. Reasonable agreement is found between the analytical results and measured data up to the phase transition temperature. The elastic constants are calculated from the stress-strain curves obtained from the NVT ensemble, the initial lattice constant of which is modified based on the result of the NPT ensemble. The analytical results agree reasonably well with the measured data up to an intermediate temperature.

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Using an elastic-plastic-viscoplastic constitutive equation, an equation relating stress wave speed, particle velocity and strain is derived. The derived equation is of the same form as that of the theory of the elastic-plastic stress wave (Karman's theory). However, contents of both equations are different because the former takes into account the viscoplastic strain and the latter does not. It is shown from numerical values for the derived equations that the stress wave speed decreases with increasing particle velocity and the stress wave speed corresponding to particle velocity increases with increasing strain rate. Also, it is shown that the propagation speed corresponding to particle velocity agrees qualitatively with the experimental results. Moreover, every equation of existing theories of the elastic-plastic, elastic-viscoplastic and longitudinal elastic stress waves is derived in consistent mathematical form from the theory of elastic-plastic-viscoplastic stress waves.

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In a bolted joint, failures usually initiate at the first root of the bolt thread. However, rupture around the bolt head is sometimes reported for a tap bolt because of high stresses produced by tightening torque applied to the bolt head. It is also well known that manufacturing errors of internal threads in a tapped hole are generally much larger than those of external threads. In this paper, mechanical behaviors of bolted joints in various clamping configurations are analyzed using FEM as an axisymmetric elastic contact problem, and the effects of nominal diameter, friction and pitch error upon stress concentrations are evaluated for through bolts, studs and tap bolts. In addition, the tightening process and strength of bottoming studs, which have seldom been studied despite of its good performance in preventing stress concentration at the runout of threads, are also investigated.

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A method for simulating the motion of grains in mushy-state forming of magnets is proposed on the basis of the distinct element method. The grains of the magnet are modelled to be a lot of elliptical elements, and the effect of the liquid phase on the motion of the grains is treated as viscous resistance to the movement. The motion of individual grains is obtained by solving the equations of motion for a mail time step under the action of elastic repulsive, frictional and viscous forces. Plastic deformation of a metallic capsule containing the magnet is calculated by the viscoplastic finite element method, and the obtained motion of the interface between the capsule and the magnet is used as a boundary condition in the distinct element simulation. Mushy-state plane-strain upsetting of a rare earth magnet contained in a steel capsule is chosen as an example of the simulation. The calculated degree of grain alignment is in good agreement with that obtained by a model experiment using acrylic grains, a plasticine capsule and Vaseline.

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Piezoelectric actuators can induce various amounts of strain upon being activated. Therefore, it is possible to reduce the stress concentrations under various external load conditions by distributing piezoelectric actuators in region expected to be subjected to high stress before external load application. In this study, we treat the optimal relaxation of stress concentrations in adaptive plates with holes using piezoelectric actuators Adaptive plate models are concerned with simple actuator/substrate systems in which the substrates are infinite isotropic plates with a circular hole, an elliptical hole or two circular holes of equal diameter, and actuators are bonded to the plate surfaces near the holes. To examine the performance of the adaptive plates, we calculate the optimal voltage that must be applied to each piezoelectric actuator to minimize the maximum stresses in the substrates under some external load conditions.

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This study is concerned with the thermal stress analysis of a butt adhesive joint which contains circular holes and fillers in the adhesive and is under non uniform temperature held. In the analysis, the adherends and fillers are assumed to be rigid and the adhesive is replaced with a finite strip containing holes and rigid fillers and the thermal stress distribution in the adhesive is analyzed using a two-dimensional theory of elasticity. The effects of size and location of circular holes and rigid fillers on the stress distributions at the interface and at the filler and hole peripheries are clarified by numerical calculations. For verification, photoelastic experiments were performed using an epoxide resin plate containing small holes and fillers, to model an adhesive in the joint. The analytical results were fairly consistent with the experimental ones.

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This paper is concerned with an analytical formulation and a numerical solution of the thermal stress and deformation for axisymmetrical shells of functionally graded material (FGM) subjected to thermal loading due to fluid. The temperature distribution through the thickness is assumed to be a curve of high order, and the temperature field in the shell is determined using the equations of heat conduction and heat transfer. The equations of equilibrium and the relations between the strains and displacements are derived from the Sanders elastic shell theory. The fundamental equations derived are numerically solved using the finite difference method. As numerical examples, functionally graded cylindrical shells composed of SUS304 and ZrO₂ subjected to thermal loads due to fluid are analyzed. Numerical computations are carried out for various compositional distribution profiles in FGM. The results show that the present method gives correct temperature distributions and that the temperature distributions, stress distributions and deformations vary significantly depending on these compositional distribution profiles.

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A structure with characteristics that are only slightly modified by any changes of external forces, boundary conditions, and productive errors has advantages from the engineering point of view. This kind of structure is called "robust structure". Robust structure problems are classified into the narrow sense and the broad sense. In this paper, dynamic robust structures in the broad sense are discussed. A design method of dynamic robust structures is proposed, which takes an eigenvalue as a reference function. The following three points are clarified from numerical examples of bar and plate structures. First, a dynamic robust structure can be designed when an eigenvalue is chosen as a reference function. Then a structure the mass of which is concentrated near the antinode of the vibration can gain the robustness. Finally, robust structures have advantages when the control system is designed since the optimum control gains have been only slightly affected in comparison with other designed structures.

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Thermoelectric power generation is an electric system used to directly translate a temperature difference to a potential difference based on the Seebeck effect. Although thermoelectric generation as a small power source in spacecraft has been developed mainly in the U.S., the generation system did not spread industrial power generation because of high manufacturing cost. We proposed a structural concept of a FGM (functionally gradient material) compliant pad to reduce the concentration of thermal stress between the thermoelectric cell and the wall of the heat exchanger for a SiGe thermoelectric conversion system as industrial power generation. This paper describes a graded compositional design of the compliant pad for reducing the residual stress caused by a sintering process. The graded compositional profile in Pd/Si₃N₄ and Si₃N₄/Cu graded interface was examined by a local approach method which was proposed in this study. As results, a concentration of residual thermal stress in the thermoelectric cell was reduced by an application of the compliant pad with Si₃N₄-rich FGM. Also, the application of FGM to compliant pad had no effect on temperature distribution in the module.

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A cantilever beam subjected to a tip load is widely used in machine elements, for example, the boom of a jib crane, an arm of an industrial robot, and an aircraft wing. In such elastic elements, a large deflection characteristic is observed without exceeding the elastic limit of the materials. This property is of both analytical and technological interest. It is necessary to analyze the large deflection behavior to achieve high reliability of the structural components. In this report, an elastica problem of a spring-hinged cantilever beam with an inclined concentrated load applied at free end is examined. Several analytical formulae are derived in terms of elliptic integrals for arc length, vertical and horizontal displacements, bending moment, curvature and bending stress. Moreover, a large flexural-bending test is performed on a thin PVC plate in order to assess the applicability of the theoretical solutions. Experimental data agree very well with the result of the large-deflection theory.

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In this paper, we propose a constitutive equation for cyclic viscoplasticity in which the viscoplastic potential function, the modified Prager-Ziegler kinematic hardening rule, and the Ramberg-Osgood law are incorporated. The applicability of the proposed constitutive equation to the deformation of 60Sn-40Pb solder alloys is Verified by a series of basic experiments, including a creep test and cyclic tension-compression test, which are performed at 303K, 323K and 343K. Moreover, fatigue tests are conducted at 303K, 323K and 343K to obtain the relation between the plastic strain work density per unit time and the number of cycles to fatigue failure. As a result, it is found that the fatigue failure of the 60Sn-40Pb solder can be successfully predicted using the plastic strain work density per unit time obtained from the simulation based on the constitutive equation.

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In this paper, a collision of an elastic sphere is analyzed by the indirect fictitious-boundary integral method with the time-dependent fundamental solution. As a result, the time variation of surface tractions and displacements in contact area are shown. Also, the maximum collision force and its acting duration are analyzed, and these results are compared with the quasistatic Hertz's solution in the elastic-contact theory.

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This paper describes a method for evaluating material properties of multilayered system from data obtained by indentation testing. The measurement information collected from the penetration force-depth curves are employed for identifying elastic moduli of thin films. The axisymmetric indentation problem is first analyzed on the basis of the three-dimensional axisymmetric elasticity theory. Then, an analysis of an elastic contact problem, in which an elastic axisymmetric indenter penetrates an elastic half-space coated with multilayered thin films, is presented. Next, an inverse procedure for determining Young's modulus, Poisson's ratio of thin films and radius of the contact area is described under the condition that the elastic moduli of the substrate and indenter, and thicknesses for layers are known. For an inverse analysis using the complex method, effective sampling of data obtained by penetrating indenters with various radii of curvature into the coated substrate is presented.

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A new method is proposed for evaluation of the temperature dependence of Young's modulus. Even if a material shows linear elasticity, the apparent stress-strain curve will be nonlinear when the measurement is carried out during heating. An optimization problem combined with finite element analysis is applied to the evaluation of the temperature dependence. The objective function of this problem to be minimized is the root mean square value of calculated stress which deviates from measured one, and the variable is the modulus as a function of temperature. It was found that the temperature dependence of a plastic material was well approximated by this method with a polynomial expression for the case of small temperature change. Although approximation was not so good for the case of large temperature change, this method is expected to work well with a better optimization process.

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A model of a surface-mounted gull-wing-leaded device was proposed for elastic-plastic-creep finite element analysis. Stresses and strains of a solder joint und ercyclic thermal loads were analyzed. Plastic strain and creep strain were calculated, even for the temperature-change domain. The results of cyclic hysteresis behaviors were compared with those analyzed based upon the conventional model in which both the dependence of temperature on the yield stress of the solder and creep behavior in loading and unloading temperature cycling were ignored. It has been found that it is essential to consider these factors. The effects of the parameters such as temperature increments, strain rate and dwell time on the analytical results of stress were also studied.

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To understand the ink How mechanism in mimeographing, the mechanics of fluid-saturated poroelastic solids is applied to analyze the elastic deformation of and the ink How through a screen/printing-master layer which is pressed from below by a press roller and subjected from above to hydrodynamic lubrication pressure induced between a printing drum and an ink roller by rotation. Special attention is placed on how the elastic nonlinearity, found in our experiment, of the layer affects the ink flow through it. The numerical calculation has shown that the nonlinearity influences to some extent on the ink out-flux history and to a greater extent on the ink volume transferred to a printing paper sheet; however, the conclusions obtained in the previous paper where the linear elasticity was assumed do not need to be changed.

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This paper is concerned with the exact solution of a coated half-space subjected to a point heat source which acts in the interior of the layer. The problem is formulated by Muki's method using Hankel transforms. We perform the inverse integrals involved analytically, and thus obtain a closed form solution, which is represented by the associated Legendre function of the first kind. Some considerations are given for stress singularities when the point heat source is located at the interface, and it is found that the shear stress becomes singular at the heat source point. From the present solution, some existing solutions of special cases can be derived.

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Two dimensional elastodynamic analysis is presented for the intensity evaluation of elastic wave backscattering from a gradient inhomogeneous layer. A linear inhomogeneous layer element (LILE) is a new fundamental element of the analysis. Stacking of LILEs can create an excellent analytical model of a gradient inhomogeneous layer. The method of developing the model has been interpreted. Application of the model has been demonstrated for the reflection and transmission problem of obliquely incident SH waves impinging on a gradient inhomogeneous layer. Their calculated intensity of reflection can be verified using the conservation law of energy. As a result, excellent adaptability of the model to an acoustic impedance variation shows that it is a viable analytical tool for such a difficult dynamic problem involving an inhomogeneous material.

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This paper deals with the connections between the local geometries of associated paths of stress and strain under plastic deformation. This is a classical topic; nevertheless, some practically important aspects remain to be investigated in depth. The studies of the mutual relations between these paths reported in the literature have been performed in plane deformation, where the shape of stress path on the (σ₁, σ₂) plane is compared with the strain path shape on the (ε₁, ε₂) plane. However, even though plane stress deformation is assumed, there exists an ε₃ component. Hence, the planar shape of strain path on the (ε₁, ε₂) plane does not show the real path shape, but is only the projection of the three-dimensional path to this plane. The strain in plastic deformation is always constraint on the deviatoric plane passing through the origin, and its shape correlates with the shape of deviatoric stress path. Therefore, the intrinsic correlation between strain and stress should be discussed on that plane, where Levy-Mises theory gives a very simple correspondence showing that the stress vector changes its angle with a rate equal to the curvature of the strain path. Taking into account the stress rate dependence in the constitutive equations used, the effect of this dependence on the shape correspondence between these paths is discussed.

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In an analysis of the deformation of rate-dependent sheet materials, the rate of change of strain rate is a significant factor, as well as the strain rate sensitivity m value. The extended theories of plastic instability combined with the rate of change of strain rate are presented, and reveal a significant role of accelerated strain rate on increasing instability strain in uniaxial and biaxial tension. This prediction was verified experimentally on three kinds of ductile sheet materials which indicate different rate dependencies. In order to arbitrarily change strain rate, a computer-controlled system was introduced into uniaxial tension tests and stretch flange forming tests. The effect of accelerated strain rate was recognized on the instability strain in the experimental results. By the comparison of the experimental results with calculated results, it was suggested that instability strain increases as work hardening during deformation increases with accelerating strain rate.

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By the use of a similar numerical method as that in the previous paper, the forming limit strain of bonded sheet metals is investigated, in which the FEM is applied and J2G (J₂-Gotoh's corner theory) is utilized as the plasticity constitutive equation. Bonded two-layer sheets and sheets bonded with dissimilar sheets on both surface planes are stretched in a plane-strain state, with various work-hardening exponent n-values and thicknesses of each layer. Processes of shear-band formation in such composite sheets are clearly illustrated. It is concluded that, in the bonded state, the higher limiting strain of one layer is reduced due to the lower limiting strain of the other layer and vice versa, and does not necessarily obey the rule of linear combination of the limiting strain of each layer weighted according thickness.

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The basic deformation properties of a polyurethane-series shape memory polymer film were investigated experimentally. The main results are summarized as follows. The modulus of elasticity below T_g is about 100 times larger than that above T_g. The loss tangent in the vicinity of T_g is about 0.6. In the case of cyclic deformation above T_g, yield stress decreases and irrecoverable strain increases with increasing number of cycles. The cyclic deformation properties vary significantly in the early cycles but vary only slightly afterwards. The strain obtained by loading at high temperature followed by unloading at low temperature is almost equal to the maximum strain. The residual strain does not vary under thermomechanical cycling, which indicates the shape fixity stability of the material under cyclic deformation. The rate of strain recovery by heating after several thermomechanical cycles is more than 95%.

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When an explosion occurs in chemical plants, the explosion pressure leads to collapse of pipes and equipment. Even if pipes are not destroyed immediately by the explosion pressure, the cumulative damage caused by the sequential explosion pressure will bring about collapse. Therefore, the disaster simulation program, which takes the cumulative damage into consideration, has been developed. In this program, three-dimensional explosion pressure applied to pipes can be calculated, and the equivalent stress acting on the connecting bolts of pipes can be analyzed. The cumulative damage is estimated by use of the obtained stress, Manson-Coffin's rule and Miner's rule. As an example, the cumulative damage over time for pipes in a model plant has been analyzed. As a result, it is shown that the proposed computer program is very useful for reliability evaluation and installation of pipes in chemical plants.

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