Due to a strain-induced martensitic transformation (SIMT), a strength, a ductility and a toughness of the TRIP steel are enhanced. Recently, a low-alloyed high strength steel based on the TRIP steel is under development and its application to an impact absorption member is being investigated. Therefore, an evaluation of an energy absorption characteristic of the TRIP steels is quite essential. An experimental approach provides us the SIMT behavior under only static deformation since it is difficult to capture a moment of the phase evolution and temperature rise for the impact deformation. Thus, a computational approach with an appropriate constitutive model for TRIP steel can be powerful for its evaluation. Here, the impact compressive deformation behavior of TRIP steel is experimentally studied by the split Hopkinson pressure bar (SHPB) method at room temperature. Then, a finite element equation with the constitutive model for the TRIP steel proposed in the past is derived from a rate form of the principle of virtual work based on an implicit time integration scheme. After the results between the computation and the experiment for an impact compression are compared to confirm an validity of the computation, an impact deformation behavior under tensile deformation at a various temperature are evaluated.

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In this paper, an equivalent elastic modulus of unsymmetrical hexagonal honeycomb is studied by using numerical results of FEM. The force is applied in such a direction parallel to one of the cell walls. A rotation of a unit around the joint point of three cell walls is necessary to simulate a deformation of honeycomb exactly, because of anisotropy of the unsymmetrical honeycomb. The deformation of honeycomb consists of two kinds of deformations: one is a deformation inside the unit, which is caused by the bending, stretching and shearing of cell walls and the rigid rotation of inside unit, and the other is relative displacement among units. The equivalent elastic modulus is determined from the relative deformation among units Also, the accuracy of the equivalent elastic modulus obtained in this method is found to be very high in comparison with the numerical results because of considering bending, stretching and shearing deformation of cell walls.

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A loss factor of a polymeric material which influences its vibration damping capacity strongly is high in value nearby its glass transition temperature. Therefore, when the constituents of a polymer-based composite material are various in their glass transition temperatures, the magnitude of the macroscopic loss factor of such a composite may be expected to be high within wider range in temperature. In the present study, a shape memory polymer (SMP) particle/SMP matrix is used as a sample material and its macroscopic complex modulus and loss factor are derived explicitly by using the equivalent inclusion method combined with the Mori-Tanaka's theorem. Consequently, for the case of a five mode type of distribution of the glass transition temperature of particle whose aspect ratios is 0.01, the value of the macroscopic loss factor becomes higher than that of the monolithic SMP and it becomes constant within the temperature range from 30℃ to 70℃.

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To help with the effort to increase the rate of surface coverage of vacuum insulation panels (VIPs), which provide high insulation efficiency, we have quantitatively investigated the relationship between the increase in thermal conductivity against the strain generated when VIPs with multiple film layers were bent. We used the results by using a commercial structural software to develop a method for predicting the amount of strain in VIPs constructed of multiple film layers when they are bent. Testing demonstrated that it can predict the amount of strain to within〜3.1% for various VIP shapes and molding methods. This high level of accuracy will help increase the rate of surface coverage and thus help in the effort to conserve energy in various fields.

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Numerical model for simulation of magnetoelastic interactions in polycrystalline ferromagnets is proposed. In ferromagnetic materials, individual grain is divided into many magnetic domains. In the demagnetized state, domains magnetized parallel to one of the easy axes are randomly distributed. When magnetic field or stress is applied, domain walls move and rotation magnetization starts to occur. In this study, change in the total volume of domains of each direction is calculated for every grain. Volume exchange between domains is assumed to be proportional to the difference of internal energy. The constant of proportionality is decided from the magnetization curve. Rotation magnetization is also introduced to the simulation. Magnetization direction of the most preferable domains is rotated so as to minimize the sum of internal energy. Results are compared with the experimental results, showing that stress dependence of magnetic properties can be predicted and that the effect of heat treatment can be explained by only two parameters.

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In order to develop a brain spatula or a brain retractor made of shape memory alloy (SMA), the mechanical characteristics of copper and TiNi SMA used for the brain spatula were compared based on the tensile deformation properties, and the dimensions of the SMA-brain spatula were discussed. The fatigue properties of both materials were investigated by the alternating-plane bending test. The results obtained can be summarized as follows. (1) Based on the yield stress and modulus of elasticity of copper and SMA, the bending deformation properties of the SMA-brain spatula were estimated by assuming the condition to use the brain spatula as bending of a cantilever. With respect to the SMA-brain spatula for the same length and width as the copper one, if the thickness of the SMA-brain spatula is 1.33 times as large as that of the copper one, the SMA-brain spatula can be easily bent by small force and can hold the necessary shape of an opened part of the brain. (2) With respect to the alternating-plane bending fatigue, the fatigue life of both copper and SMA in the region of low-cycle fatigue is expressed by a power function of maximum bending strain. The fatigue life of the SMA is longer than that of the copper by 100 times. (3) The above-mentioned properties of the SMA obtained in this study can be applied to the development not only for the brain spatula but also for other retractors and instruments used in other surgery operations.

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Spinning process and pretension treatment are used for Al-Alloy composite tanks. The spinning process develops coarsened grains and the pretension treatment shears precipitation particles. These changes of material properties is considered to affect the fatigue characteristics of age-hardened metals, such as Al-alloy 6061-T6. In this study, the effect of the prestrain and grain size on fatigue crack growth characteristic of age-hardened Al-alloy 6061-T6 was investigated. Fatigue tests were performed with a rotating bending fatigue test machine. The specimen with an artificial hole were prepared to observe mode I fatigue crack. Coarse-grained plain specimens were used for observation of mode II fatigue crack. Mode I fatigue crack growth rates were decelerated a little by the pretension in the stable crack growth region. But in the case of mode II fatigue crack, the crack growth rates of prestrained specimens became about ten times faster than those of the non-prestrained specimens. The observation of the fatigue process showed that the slip bands due to prestrain accelerate the mode II crack growth. The specimens taken from a real high pressure tank showed similar crack growth characteristics.

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In this study, the effect of pre-fatigue on the impact tensile properties of the laser welded butt joint between three kinds of steel plates, an ordinary steel for vehicles and two high strength steels with the tensile strength level of 590 and 980MPa, were investigated by split Hopkinson bar apparatus. For comparison, quasi-static tensile tests were also performed to examine the effect of strain rate on their strength and elongation. It was found that the effect of pre-fatigue on the tensile strength of welded joints is small. However, the elongation or fracture strain of 980-590 joint specimen subjected to low cycle pre-fatigue was much smaller than that of virgin (not pre-fatigued) joint specimen. These results were observed in both static and impact tensile tests. It was also found that a pre-fatigue parameter, newly introduced here, is useful to indicate a danger of pre-fatigue.

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The Weld Overlay has been used in several countries as an effective method to repair the stress corrosion cracks in nuclear power plant piping. However, the method to evaluate the plastic collapse stress for the pipe repaired with Weld Overlay has not been proposed and the limit load criterion for single uniform material has been used to design its structure by now. In this paper, the equations to evaluate the plastic collapse moment for the pipe repaired with Weld Overlay have been derived considering two layer materials. Moreover, several numerical examples are given to show the validity of Weld Overlay. The equations given in this paper are simple to use like the limit load criterion showed in present standards such as JSME Rules on Fitness-for-Service for Nuclear Power Plants or ASME Boiler and Pressure Vessel Code Section XI, and they can not only be used to evaluate the fracture of the pipe, but also be applied to design the weld structure.

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When a flaw is detected in a stainless steel pipe during in-service inspection, the limit load criterion given in the codes such as JSME Rules on Fitness-for-Service for Nuclear Power Plants or ASME Boiler and Pressure Vessel Code Section XI can be applied to evaluate the integrity of the pipe. However, in the present codes, the limit load criterion is only provided for the case of a flaw with the uniform depth, although many flaws with complicated shape such as stress corrosion cracking have been actually detected in a pipe. In this paper, a limit load estimation methd is proposed considering a circumferential surface flaw with arbitrary shape, in orer to make it possible to evaluate the integrity of the pipe for general case. The plastic collapse moment and stress are obtained by dividing the surface flaw into several segmented sub-flaws. Using this method, good agreement is observed between the numerical solution and reported experimental results. Several numerical examples are also given to show the validity of this method. Finally, it can be seen that the number of the segmented sub-flaws for the semi-elliptical surface flaw is sufficient to be three from engineering judgment.

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In this study, a simple method to determine the complex stress intensity factor of interface crack problem in dissimilar materials is proposed by using the proportional method. This method is based on the fact that the singular stress field near the crack tip is proportional to r^<-0.5> and is controlled by the stress values at the crack tip node calculated by the finite element method. In the present method, the stress intensity factors of interface crack in dissimilar materials are evaluated from the ratio of crack-tip-stress values between a given and a reference problems. A single interface crack in an infinite bi-material plate subjected to tension and shear loads is selected as the reference problem in this study. The accuracy of the present analysis is verified by the comparing the present results with the results obtained by other researches. The calculation shows that the present method gives easily the accurate numerical results for the interface crack problems in dissimilar materials.

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A new method to evaluate damage state of the material containing spherical voids randomly was proposed by using the damage tensor and equivalent net stress in this paper. Tensile, torsional and tesile/tortional biaxial tests were performed the polymeric specimen containing expanded polystyrene which was regarded as three-dimensional ideal model. Then major axial strain was measured by performing image processing to a photograph of specimen, and these were compared with the equivalent net stress calculated based on voronoi tessellation. It was found that the fracture point of the specimen after tensile test was corresponding to the region of the highest equivalent net stress. In addition, major axial strain tended to increase in the region of the high net equivalent stress under conditions of monotonic loading with tension, torque and biavial, suggesting that damage state of porous materials was quantitatively estimated through the present method.

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Tests of pure titanium sheet (JIS # 1, 0.5mm thick) subject to biaxial stress were carried out in order to elucidate the anisotropic plastic deformation behavior for linear stress paths. Contours of plastic work and the directions of plastic strain rates at different levels of plastic work were observed in the first, second and fourth quadrants of stress space. Since the maximum equivalent strain obtainable using cruciform specimens is limited to 0.005, combined tension-internal pressure tests were carried out in order to achieve a maximum equivalent plastic strain of 0.085. These tests used tubular specimens made with a single lot of test material. Additionally, in-plane tension-compression tests were performed to observe the strength differential for the lot of pure titanium sheet between tension and compression. Using the observed data, the applicability of conventional anisotropic yield functions, such as Hill's quadratic function, the Yld 2000-2d function and Cazacu's function, to the accurate prediction of the plastic deformation behavior of the pure titanium is discussed. The measured work contours and the directions of plastic strain rates were in fair agreement with those calculated using the Yld 2000-2d and Cazacu's yield function. However, the differential work hardening behavior of the pure titanium sheet could not be accurately reproduced using these functions.

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Tensile behavior of two commercially available TRIP aided dual phase steels was studied by means of in situ time of flight neutron diffraction. The deformation was characterized by three stresses, P1, P2 and P3; plastic flow starts in the ferrite matrix at P1 and the deformation induced martensitic transformation and the plastic deformation in austenite occur respectively at P2 and P3, which are determined from neutron diffraction results. Work-hardening and a tensile strength versus uniform elongation balance are controlled by adjusting these three stresses.

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For guaranty of quality of the non-based adhesive sheet, one kind of adhesive used in flat panel display (FPD), damage of adhesive in a laminate process should be controlled to evaluate the interface strength. Standard examinations are not suitable for evaluating the interfacial strength because measured the peel force F includes other influences of peeling. In this paper, we developed Multi Axes-driven Peel method (MAP) to measure the peel force F from 30 to 180 degrees of the peel angle. The delamination energy and the energy dissipation were evaluated considering energy balance in steady state. This delamination energy dependency on the peel angle was discussed to observe the peel front. Then peel force in a laminate process can be obtained by the Y-type peeling test. The prediction of peel force in the Y-peel test using the delamination energy and energy dissipation measured by MAP were in good agreement with the experimental result.

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Brittle fracture behavior of a light cure composite resin was studied using a high-speed extensometer. The single-edge-notched tensile specimens were fractured with a special loading jig so that it could split and fly away after the fracture. The load and displacement diagram, i.e. the external work applied to the specimen was partitioned into three parts: the elastic energy left in the fractured specimen, the nonelastic energy due to viscoplastic deformation and the fracture energy for creating new surfaces. These energies were then determined and correlated with the fracture load. Energy release rates were also evaluated, and the results were discussed.

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This paper deals with a multi-objective optimization problem of crushing energy absorption of basic box-type column structures. This paper has tried to show the influence of dimensions of polygon, thicknesses of outer wall and inside diaphragms to the absorbing behaviors and the crushing peak force by the CAE simulation using LS-DYNA. Then, this design problem is formulated as a multi-objective design optimization problem considering the maximization of total absorbing energy by crushing of column, and the minimization of crushing force peak during energy absorption. The response surface approximation technique is adopted to get the Pareto optimum with small numbers of CAE simulation of crushing. The suggested formulation is applied to solve the box-type shell structures with diaphragm and hexagonal-type shell structures with diaphragm. Finally, it is found that the shell structures with diaphragm, which connects the center of cross section and midpoint of each edge of side wall, show better energy absorbing performance in comparison with the structures with diaphragm connecting the center of cross section and the apexes of side walls.

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The simulation of the head subjected to a lateral rotational impact was conducted to understand the mechanism of the diffuse axonal injury (DAI). It is known that the diffuse axonal injiury frequently occurs in motor vehicle accidents. Gennarelli et al. proposed that DAI occurs while ahead is subjected to rather a lateral rotational impact than an anterior-posterior or oblique impact. The obtained result shows that the higher stress occurred in deep area of brain near the leading edge of a falx cerebri and tentorium cerebelli. It was confirmed that the greater stress areas of the brain matched the fact that DAI often involve the injury in a corpus callosum and a brain stem. Moreover, the localization of brain function in the higher stress areas corresponds to the residual disability in DAI. We expect that the injury in a brain stem and cerebral limbic system is the essential of DAI.

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