Molecular dynamics simulations on the shape memory effect are carried out by using the EAM potential for Ni-Al alloy. As a preliminary calculation, the stable crystal structures are investigated, so that both bcc and martensite phases are obtained and the temperature-dependent transformation can occur. As a result, it is revealed that 60-70% Ni models show the martensite structure at low temperature, and bcc at high temperature, and the transformation temperature depends on the Ni content. In order to simulate the shape-memory behavior, a series of loading, unloading, heating, and cooling conditions is imposed for 68% Ni model. In the loading process, the model is deformed by the motion of variant boundaries, and a large deformation is observed. The deformation does not disappear even the model is unloaded. However, the model recovers the original shape when it bears the heat treatment process incorporating the phase transformation to bcc structure.

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As single crystal of lead zirconium titanate (PZT) is difficult to produce, all of its ferroelectric properties are not clarified perfectly. In this paper, the ferroelectric properties of PZT single crystal have been identified computationally from ones of PZT ceramic by steepest decent method and multiscale finite element modeling based on a crystallographic homogenization method. Crystallographic homogenization method enables us to predict macroscopic properties of ceramics considering microscopic in-homogeneous structure in an aggregation of crystal grains. Crystal morphology of PZT ceramic has been measured by SEM·EBSD technique, and it has been introduced to microscopic finite element model. Then, the ferroelectric properties of crystal grain were surveyed by steepest decent method to correspond its macroscopic ones to experimental values of PZT ceramic. The proposed computational procedure has been applied to barium titanate, and its validity has been proved by comparison of identified ferroelectric properties with already-known ones of single crystal. Finally, the identified ferroelectric properties such as elastic compliance, dielectric and piezoelectric constants were presented for PZT single crystal.

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The dynamic fracture problem of a functionally graded piezoelectric slab containing a crack perpendicular to the boundaries is considered. It is assumed that the electroelastic properties of the medium vary continuously in the thickness direction. Based on the integral transform techniques, the problem due to the in-plane mechanical impact loads is reduced to the solutions of a singular integral equation. An internal crack and an edge crack are examined. Numerical calculations are made for the variations of the dynamic stress intensity factors and the dynamic energy density factors versus time while the geometric parameters and the material nonhomogeneity are changed.

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In the packaging design of electronic devices, the reliability margins for each design specification have been reduced because of high-quality specifications. Therefore, at an early stage of design, it is important to analyze various design margins such as signal integrity, cooling characteristics and thermal fatigue life of solder joints for a number of design solutions, taking into consideration the element of uncertainty in the design. In this paper, the Response Surface Method (RSM), the First Order Reliability Method (FORM) and Structural Equation Modeling (SEM) were introduced in order to realize the reliability evaluation and optimization in the multidisciplinary design. This method was applied to the packaging design of CPU (Central Power Unit) module for the purpose of the validity verification.

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Fractal analysis has been widely used to characterize the fracture surface. If has been recognized that the local Hurst exponent, which is based on the concept of self-affine fractal, is useful to detect the transition point of fracture surface. For the calculation of the local Hurst exponent, a high resolution profile is needed. To measure the profile, however, much time and effort are needed. Therefore, it is difficult to calculate all profiles of fracture surface and evaluate the feature of fracture surface in detail. In this study, a new method to calculate the two-dimensional local Hurst exponent is proposed. It is realized to evaluate the feature of fracture surface by using the local Hurst exponent. To investigate the validity of the two-dimensional local Hurst exponent, the calculation was applied to the gray-scaled images in which the stretched zone was observed and the width of stretched zone (SZW_c) was measured. Consequently, SZW_c calculated by the two-dimensional local Hurst exponent and detected by the human observation have the good agreement. Therefore, it was found that the two-dimensional local Hurst exponent is useful to detect the transition point of fracture surface.

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This paper deals with the mutual interference of multiple two-dimensional surface cracks in a surface coating layered material under thermal stresses due to rolling contact with heat input. Contact loading is simulated as a contact pressure load with both the normal and shear components having parabolic distribution. In the present crack analysis, the surface cracks are replaced by the distributed edge dislocations, and the crack face friction is not considered. The problem is reduced to simultaneous singular integral equations for dislocation densities. The integral equations can be solved numerically by considering the nature of the singularities at the crack tips. The numerical results of the stress intensity factors showing the effects of the mutual interference of a pair of surface cracks are given for some tribological material coatings on a steel substrate. The effects of the frictional coefficient, the heat input strength, the crack length and the coating thickness upon the magnitude of the stress intensity factors and it's mutual interference are considered numerically.

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The fatigue limit diagram shows the allowable stress zone for constant amplitude fatigue loading. It was shown is this study that fretting fatigue failure occured in the case of variable amplitude loading condition even when every stress amplitude was kept below the fretting fatigue limit diagram. The reason why such a phenomenon occurred was examined using repeated two-step loading fretting fatigue test. The first step stress of the repeated two-step loading was chosen as R=-1 and the second step stress was with high mean stress. A non-propagating crack was formed by the first step stress even well below the fatigue limit. This crack functioned as a pre-crack for the second step stress with high mean stress. Consequently, fatigue failure did occur even when every stress was kept below the fretting fatigue limit diagram of constant amplitude. The fatigue limit diagram does not necessarily guarantee the safety in the case of variable amplitude loading.

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Fatigue behavior of welded joints was studied on a ferritic stainless steel, SUS 444. Plate specimens with weld zone located at the center of gauge section were used for fatigue strength evaluation and two types of CT specimens were employed for crack propagation tests. The fatigue strength of the welded specimens decreased remarkably compared with that of the base metal. Multiple cracks initiated at the toe of weld, then grew and coalesced, leading to final failure. In order to discuss causes of the reduction of fatigue strength in the welded specimens, additional fatigue tests were performed using the annealed specimens and the specimens whose reinforcement of weld was completely removed. The former specimens showed only a slight increase of fatigue strength compared with the welded specimens, while the latter specimens exhibited nearly the same fatigue strength as the base metal. Based on these results, it was concluded that the effect of residual stress was relatively small and thus the significant decrease of fatigue strength in the welded specimens was attributed to the stress concentration resulting from the geometry of the reinforcement of weld. Furthermore, it was found that the crack propagation resistance of HAZ (Heat Affected Zone) and weld metal was higher than that of the base metal due to higher crack closure level.

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This paper focused on configuration of matrix cracks for plain-woven CF/Epoxy composites under cyclic loading. Load-controlled fatigue tests were conducted under tension-tension cyclic loads at a stress ratio R of 0.1 and a frequency of 5 Hz in the laboratory condition. The number and the location of matrix cracks were observed for the damaged specimen by using an optical micro-scope. The modulus reduction ratio was continuously measured during fatigue tests. The experimental results showed that the configuration of matrix cracks was quantitatively estimated with the number of matrix cracks and statistical parameters (configurational coefficient and average distance between cracks). For parallel-sided specimens, the average distance between cracks became shorter with an increase of number of matrix cracks. It was found that the relationship between configurational coefficient and the modulus reduction ratio was linear.

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In this study, firstly, composites which consist of shape memory alloy (SMA) fiber and epoxy matrix are fabricated. Secondary, the distribution of unique performances in shape memory alloy composite (SMAC) such as creating of internal stress in matrix and deformation of composite are investigated by using photoelasticity and digital image correlation under thermo-loading process (heating-cooling process). Furthermore, temperature distribution on the surface of composite is investigated by using infrared radiation thermometry. The results are as follows; (1) Deformation of composite becomes large due to austenite transformation of fiber during heating. Local strain of composite has distribution along the longitudinal and transversal direction of specimen. Also, recovery of deformation appears during cooling. (2) Internal stress in matrix changes during heating. There exists distribution of internal stress along not only transversal direction but also longitudinal direction of specimen. Also, recovery of internal stress is observed during cooling. (3) The surface of composite has temperature distribution along the transversal direction of specimen. The surface temperature reaches at 45.0°C when temperature of fiber is 84.4°C.

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High-order Lamb waves of symmetric mode are applied to flaw detection in steel plates. In inspection of the plates, the lowest symmetric mode Lamb wave is preferable, because effect of the velocity dispersion, which distorts the waveform, is small in the low frequency region. However, for thick plates, the frequency should be lowered, and the wavelength becomes large, consequently. In this study, we suggest to make use of high-order Lamb wave at frequency of its maximum group velocity, in order to avoid the interference with the other modes. Electromagnetic acoustic transducers (EMATs), each of which consists of an electromagnet and a meander line coil, are designed for three modes of Lamb wave in 6 mm-thick steel plate, using theoretically obtained dispersion curves. Optimum magnetic field strength is investigated, ensuring that the wave generation and detection are based on the magnetostriction. Dispersion curves are measured by sweeping the excitation frequency, which reveals the optimum frequency. Echoes from drilled holes are detected and the flaw detectability of each mode is discussed.

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Structure of metallic hollow spheres (MHS structure) is one of ultra-light porous metals. The ultra-light structure to car parts has a possibility to reduce CO₂ emission because MHS structures can reduce the car weight without decreasing the rigidity and energy absorbing performance. In this research, to estimate the performance of MHS structures, deformation behaviour of single MHS and the structure are examined by uniaxial compression test and bending test. In the compression test, plateau stress appears for the structure of low density. MHS diameter, shell thickness and carbon content have influences to the magnitude of plateau stress and the mechanical properties mainly depend on the density of the structure. In bending test, MHS structure fails in tension side with very low-tensile stress.

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The effect of mechanical alloying conditions on the characteristics of mechanically alloyed powder (MA powder) and its sintered alloys were investigated. The difference in sintering behavior between the MA powder and the elementally mixed powders by a V-blender (V-blended powder) and the microstructure and shape memory characteristics of the sintered alloys were also examined. The MA powder was fabricated by using a planetary ball mill and was sintered by a pulse-current pressure sintering equipment at various temperatures. The powder agglomerated and cold-welded and its particle size became larger with an increase in milling time. The mixture of Ti and Ni powders changed into an amorphous state by processing for 3.6 ks more than 500 rpm. The assintered alloy of the MA powder showed more homegeneous phase of TiNi than that of the V-blended powder produced in a same manner, however the former showed a lower density than the latter due to a larger particle size of its MA powder of before-sintering. The solution-treated alloy of MA powder showed more uniform microstructure of TiNi than that of the V-blended powder, and the relative density of the shape memory treated alloy was 100%. The shape memory treated alloy of MA powder showed good shape memory characteristics and 750 MPa in tensile strength.

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Slip deformation in symmetric type bi-crystal models subjected to tensile load is analyzed by a finite element crystal plasticity analysis code and accumulation of geometrically necessary dislocations (GNDs) is studied in detail. Uniform deformation was expected to take place because mutual constraint of crystal grains through the grain boundary plane does not occur in symmetric type bi-crystals, but, some results of the analysis show non-uniform deformation and the high density of GNDs accumulated in the form of band. Such kind of non-uniform deformation is observed regardless of the model size and the strain-hardening characteristics. Mechanism of non-uniform deformation and accumulation of GNDs in the form of band in the symmetric type hi-crystals is discussed from the viewpoint of the boundary condition and shape change of grains after slip deformation

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In this paper, initial stress measurement theory of micropolar elastic medium by stress release method is described. This measurement method uses the circular solid inclusion cell (SI-cell) as the strain sensor. And because of the SI-cell is regard as inclusion embedded in the micropolar elastic medium, measurement theory is derived by use of the solution of the elastic material with a inclusion problem through the correspondence principle between elasticity and couple stress elasticity. The characteristic of this measurement theory is that the radius of an over coring is finite. Several examples are shown by graphical representation and numerical results.

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Cyclic loading tests were conducted basically under completely reversed strain controlled conditions with a strain rate of 1.1×10²10⁴ and a strain amplitude of 0.1 at 25°C for polyethylene (PE), polypropylene (PP), polycarbonate (PC) and polyphenylen-ether (PPE). The experimental results show that stress-strain hysteresis loops of such solid polymers have a different shape than those of metallic materials. PE, PP and PC have a small acute angle between the tangents to the loading and unloading branches and PPE has a boomerang-like shape. The viscoplastic constitutive model based on overstress (VBO) has been shown to reproduce various experimental hysteresis loops of most metallic materials but the original model is not so flexible enough to represent these shapes of polymeric materials. This paper suggests a modification method, which enable the modeling of hysteresis loops with a cusp applying to simulate the cyclic motion behavior of PE in extensive experiments within the framework of the VBO model.

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In assuring the safety of a structure, it is important to evaluate the state of structural members non-destructively. Magneto-mechanical acoustic emission (MAE) is one of the non-destructive inspections. In the previous paper, we had studied MAE signals of a pure iron using displacement and shear sensors, for the detection of the longitudinal and shear components of the signals, which were analyzed with wavelet transform. From the analysis, the following things became clear : (1) the low frequency component (150 to 300 kHz) has strong displacement sensor response coincident with the rate of magnetic induction, suggesting magnetization via the discontinuous motion of domain walls. (2) the high frequency component (400 to 800 kHz) has strong shear sensor response and is observed near magnetic saturation, suggesting rotational magnetization effect. In this paper, the character of the detected MAE signals was discussed on the effect of the preferred orientation of the texture when the carbon steel specimens (0.23 wt% Carbon) deform plasticity. As the results, it was became clear that there is a close relation between the character and its preferred orientation

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Cavitation erosion and fatigue tests were cariied out for high polymer materials ; epoxy resin, polypropylene, high-density polyethylene and polyamide 66, and the relationship between cavitation erosion resistances and mechanical properties was examined. Resistance of cavitation erosion for high polymer materials is ranged between half and 30 times in comparison with that for carbon steels. Cavitation erosion for high polymer materials is caused by fatigue as well as metals. As high polymer materials have relatively small acoustic impedance, impact loads applied by collapse of bubbles becomes so small. Therefore, the resistance and incubation period of cavitation erosion for high polymer materials can be evaluated by strain energy in fatigue by taking account of impact energy due to collapse of bubbles.

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The dynamic compressive properties of starch-based biodegradable plastics were measured using a split Hopkinson pressure bar (SHPB) method. The relationship between the stress and the particle velocity for starch-based biodegradable plastics is determined by the impedance match method by means of a SHPB over the particle velocity range of up to 13.0 m/s. In addition, dynamic stress-strain curves of starch-based biodegradable plastics were measured over a wide range of strain rates from 10^-5 s^-1 to 10⁴ s^-1, using a quasi-static compression testing machine and a SHPB method. Young's modulus and flow stress are dependent upon the strain rate. Empirical equations for 7% flow stress are derived for the strain rates from 10^-5 s^-1 to 10⁰s^-1 and from 10³ s^-1 to 10⁴ s^-1. It is also found that the attenuation of stress waves is quite large and is also dependent upon the strain rate

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The problem of determing of stresses and displacements of an elastic half space subjected to a concentrated force acting at a point of the plane surface is called Boussinesq's problem. This paper deals with Boussinesq's problems of an elastic half space with an elastic spherical inclusion. We use a body force distribution method for the stress concentration problem. For this purpose, we apply the Green's functions for axisymmetric body force problems of an elastic half space and the fundamental solution for axisymmetric body force problems of elasticity. The problem is formulated by an integral equation with unknown functions corresponding to the intensities of distributed body forces. Stress distributions around the inclusion are shown by numerical calculations and influences of elastic moduli on the stresses are also investigated.

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This paper describes the design scheme of the three-dimensional structures based on the concept of the cellular automata simulation. The structural optimization in the present method is performed according to the local rule. The penelty function is defined from two objective functions and the constraint condition. Minimization of the penalty function with respect to the design parameter leads to the local rule. The derved rule is applied to the design of the three-dimensional structure applied to a single load and the schemes to reduce the computational cost are discussed.

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In this paper, we describe the generation of an inflatable reflector. The reflector is generated by applying pressure to a membrane surface. The in-plane force of the radius direction is also applied to the surrounding boundary of the membrane. The exact differential equations to describe the deformation of the membrane are introduced. The deformed shape of the membrane is obtained by numerical calculation. Furthermore, the deformed shape that was calculated is compared with a parabola shape. The standard deviation of shape is introduced to compare the shapes. Finally, the effect of the in-plane force in the radius direction to generating the inflatable reflector is discussed.

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An anisotropic inelastic constitutive model of cortical bone was formulated to predict deformation and failure behavior in traffic accidents or falling by utilizing the framework of viscoplasticity and damage mechanics. The model can represent characteristic features of cortical bone, such as anisotropic elastic coefficients with strain rate dependency, viscoplasticity with strength anisotropy as well as strength asymmetry of tension and compression. The damage evolution equation also enables us to predict bone failure with rate dependency. Experimental data of uniaxial compressive or tensile loading tests of human cortical bone at various strain rates were used to validate the proposed model. Predicted stress-strain curves and failure points agreed well with those of experimental data at wide range of strain rates. This shows the present model can be used to predict bone failure in various impact simulations of traffic accidents or falling.

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