The mechanical characteristic of shape memory alloys (SMAs) is generally discussed, classifying it into the superelasticity and the shape memory effect. In the present study, the three-dimensional finite element method previously developed for the superelastic behavior of SMA devices by the authors has been extended to the geometrically nonlinear analysis and applied to the analysis on the shape memory effect of a SMA bar, a SMA column and a SMA honeycomb core structure. The calculated results are qualitatively reasonable and have corresponded well in part with the experimental results in the literatures. Better identifications of the material constants and the initial imperfections are necessary in order to increase the accuracy of the calculated solutions.

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Topology optimization has been successfully used in many industries, such as mechanical industries, but it often encounters numerical problems such as grayscale representations of obtained composites. A type of structural optimization method using the level set theory for boundary expressions has been proposed, in which the outlines of target structures are implicitly represented using the level set function, and optimal configurations are obtained by updating this function based on the optimal criteria. However, this method has a drawback that it does not allow topological changes that either introducing a hole in the material domain. To overcome the above two problems, this paper proposes a new topology optimization method incorporating level set boundary expressions based on the concept of the phase field method, and we apply it to the minimum mean compliance problem. First, a structural optimization problem is formulated based on a boundary expression using the level set function. Next, a time evolution equation for updating the level set function is formulated based on the concept of the phase field method, and the minimum mean compliance problem is formulated using the level set boundary expression. An optimization algorithm for the topology optimization incorporating the level set boundary expression based on the concept of the phase field method is derived. Finally, several examples are provided to confirm the usefulness of the proposed structural optimization method.

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A parameter U^*, which is independent of stress and strain, has been introduced by the authors for expressing load transfer and load paths in a given structure. The conventional U^* is defined by the energy caused by displacement at the loading point. Since it is necessary to constrain an arbitrary point during the estimation of U^*, the value of U^* cannot be calculated for a point under distributed displacement. Hence, to overcome this difficulty, a new parameter U^<**> has been developed in our study. The parameter U^<**> is defined by the complementary energy caused by force at the loading point. A mathematical formulation with complementary energy and stiffness matrices is demonstrated, which can be used for rapid and efficient computation of U^<**>. The parameter U^<**> is used for expressing load transfer in the case of a reinforced rectangular plate under the condition of out-of-plane distributed loading.

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A simplified identification method using a thermo-elastic boundary element method is proposed to estimate residual stress distribution due to butt-welds of a plate. The proposed method can identify residual stress distributions by a few measurement data, which are measured by a nondestructive (or destructive) method. It is generally known that residual stresses produced along welding lines are difficult to measure by X-ray diffraction method. However, identification of the location of the largest residual stress value is very important. The proposed methods can identify the inherent strain distribution from the measurement data near the welding lines by X-ray diffraction method, and the distribution of the residual stress and its largest value along the welding line can be calculated from the inherent strain in butt-welding plate. The validity of the proposed method is demonstrated in this paper by numerical simulations. The applicability and the effectiveness of the method are confirmed by numerical examples with and without random measurement errors.

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In this paper, a theoretical analysis for predicting the mechanical properties of lattice structures under compressive loading is proposed, and verified by comparing the analytical predictions with FEM results. This theory for estimating E^* is based on the classical beam theory, and the one for estimating σ^*_<pl> reflects the stress state for each lattice structure. It is found that the BCC structure is a bending-domminated structure, and the BCCZ structure is a compressing-dominated structure, and the f_2BCC structure is a mixed loading-dominated (stretching and bending-dominated) structure. Also, the results obtained by this theory agree well with the FEM results.

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In this paper, the elastoplastic bending collapse of square tube with partition plates subected to statically pure bending is studied by using finite element method (FEM). The roles of partition plates in the bending are investigated. In the case of square tube without partition plate, there are two types of collapse modes in the bending. The first type is a collapse mode due to buckling at the compression side. The second type is a collapse mode due to flattenig of the cross section. It is found that these collapse modes change by adding partition plates. Due to an existence of the partition plates, the collapse is controlled all by the buckling of the partition plate. There are also two types of collapse modes. The former is caused by the buckling of the compression side, and the latter is caused by the flattening of the cross section. The former is superior in energy absorption, and the latter is superior in flexural rigidity.

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Honeycomb panel is widely used as flooring or wall material in various structure, e.g., buildings, aircraft, train and so on due to high stiffness and lightness at present. Honeycomb panel, however, has a disadvantage that adhesive used to glue honeycomb core and top plate may burn by fire. On the other hand truss core panel has equivalent stiffness as honeycomb panel and is expected to be an alternative to honeycomb panel as it is safer for fire. To replace honeycomb panel with truss core panel, it is necessary to investigate the stiffness of truss core panel for bending, shear, compression and so on. Here is chosen the bending case with a three point bending model of truss core panel. Four cases of analysis with/without work hardening effect and thickness change using two types of shell formulation is performed. These cases are compared with an equivalent honeycomb model. The study showed the effect of work hardening is very important to assess bending stiffness of truss core panel. And it is also observed that the use of suitable shell formulation is necessary to obtain reliable result. In addition, the truss core panel shows comparable bending stiffness with conventional honeycomb panel.

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Precipitation strengthening is one of the effective techniques to design highly strengthened alloys. Up till now, many researchers have attempted to develop a concept that describes the strengthening effect of precipitates, and however, that contains a lot of assumptions, such as that the shape of dislocation is straight and the width of dislocation core is ignored. Recently, 3-D atom probe experiments have found the formation of γ-precipitates in γ' phases in nickel-based superalloy. Also, tensile tests have revealed that the γ-precipitates have an influence on the precipitation strengthening. In this paper, the interaction between a spherical γ-precipitate and a super-dislocation, which is a pair of two perfect dislocations, is investigated using an atomistic-continuum hybrid method. The strengthening due to the γ-precipitates is decomposed into two different strengthening mechanisms, such as stacking-fault and coherency strengthening mechanisms. We successfully simulated the interaction between the dislocation and the γ-precipitate, and focused on the role of the flexibility of dislocation and the dislocation core in the strengthening mechanism. Finally we propose an equation for the coherency strengthening based on an idea of stacking fault width in the dislocation core. The equation provides an excellent evaluation of improvements of the material strength by the strengthening mechanism.

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Functionally graded (FG) type electromagnetic (EM) wave absorbers have been proposed for the improvement in absorption performance and material strength. In this paper, we investigate coupling effects on the performance of the FG type EM wave absorbers for plate under high power injection and transient thermal stresses in the absorption systems. The coupling effects of electromagnetic field and temperature field are analyzed by weak-coupling method based on the iterative use of the analytical solutions for each field. The thermal stress field is also analyzed for a thin plate with arbitrary nonhomogeneous properties and temperature dependences. Numerical calculations are carried out for the FG type EM wave absorbers composed of epoxy resin matrix and conductive titanium oxide particles. The absorption characteristics and the magnitude of temperatures and thermal stresses are quantitatively evaluated. The effects of irradiation power and material composition distribution on the absorption characteristics and temperature distribution are then discussed. The significance of the coupling effects and the thermal stress analysis is revealed. In addition, a possibility of material design on the FG type absorber suitable for the absorption of EM wave and reduction of thermal stress is suggested.

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Recently, spark plasma sintering (SPS) known as a novel sintering technology has been used for fabricating ceramics, functionally graded materials (FGM) and composites. SPS can consolidate powders at lower sintering temperature and for shorter sintering duration compared to conventional sintering methods, such as hot-pressing or HIP (Hot Isostatic Pressing). Mechanical properties (three-point bending strength, Young's modulus and compressive strength) and biocompatibility of HAp/β-TCP FGM sintered by SPS were investigated. The FGMs were sintered at a temperature of 1073K and at a pressure of 44.6 or 66.9MPa. The FGMs compacts had higher three-point bending strength, Young's modulus and compressive strength than β-TCP. Natural bone formed on the surface of the FGM in the HAp-rich area and replacement for bone in the β-TCP-rich area. These results show that the HAp/β-TCP FGM sintered by SPS had high strength, excellent biocompatibility and controllability for graded bio-reaction.

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In this paper, stress intensity factors for a two-dimensional interfacial crack under polynomial distribution of stress are considered on the idea of the body force method. In this analysis, unknown body force densities are approximated by the products of the fundamental densities and power series; here the fundamental densities are chosen to express singular stress fields due to an interface crack exactly. The stress intensity factors of a 2D interfacial crack under polynomial distribution of stress are expressed as formulars for the reader's convenience with varying the polynomial exponent n.

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This paper investigates the thermoelectromechanical interaction among multi parallel cracks in a piezoelectric material under a uniform heat flow and a uniform mechanical load far away from the crack region. The crack faces are supposed to be insulated thermally and electrically. By using the Fourier transform, the thermal and electromechanical problems are reduced to systems of singular integral equations, respectively. The singular integral equations are solved numerically by using the Gauss-Jacobi integration formula. Numerical calculations are carried out, and detailed results are presented to illustrate the influence of the thermoelectromechanical interaction on the stress and electric displacement intensity factors. The temperature-stress distributions are also presented. From numerical results, we can find that the normalized stress and electric displacement intensity factors are under the great influence of the crack spacing and the unmber of cracks. Especially, the influence of the thermoelectromechanical interaction on the fracture behavior is complicated when the crack spacing becomes small.

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Transparent EPDM composite crosslinked by peroxide with no fillers was exposed to hydrogen gas at a maximum pressure of 10MPa, and then the behavior of blister initiation and growth in the composite after decompression was observed by an optical microscope. The critical pressure where no blisters initiated P_<H,cr> was 1-2MPa, while micrometer-sized blisters initiated in the composite at P_H>1-2MPa. It is considered that these blisters initiated due to stress concentration of micrometer-sized bubbles under an inner pressure II formed by supersaturated hydrogen molecules after decompression; then the energy release rate-tearing energy, T-of these bubbles was calculated theoretically or by FEM. Parallel to the calculation, static crack growth tests were conducted, and the threshold tearing energy for the static crack T_<S,th> was experimentally obtained. From the criterion expressed by T>T_<S,th>, the inner pressure at blister initiation II_F was estimated and then was compared with P_<H,cr>. Consequently, II_F&ap;P_<H,cr>, i.e., the critical pressure where no blisters initiated was successfully estimated in terms of fracture mechanics.

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Double-cup (DC) specimens of spot welded joint are newly produced for high strength steel sheets (HSS), and fatigue tests are conducted under three kinds of loading directions (shear, tension and mixed mode) for steel sheets with tensile strength ranging from 270MPa (mild steel) to 980MPa. The fatigue strength is degraded as the load component in the tensile direction increases. The HSSes show higher fatigue strength than the mild steel under the shear loading, whereas the fatigue strength of the JIS tensile-shear (TS) specimen is almost equal regardless of the steel grade. The deformation behavior and the stress state are investigated for the DC and TS specimens by finite element analysis. In the TS specimen, the spot weld rotates and it is subjected to the mixed mode loading. Moreover, the tensile stress of the HSS is higher than that of the mild steel under the identical load because the smaller plastic deformation takes place in the HSS. In the DC specimen, on the other hand, rotation of the spot weld is smaller due to deformation restraint around the spot weld and the stress state is close to pure shear, which may lead to the fair evaluation of the effects of the steel grade.

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Fatigue tests on carburized rotating bending specimens and carburized gears were carried out. The carburized rotating bending specimens had an oxidized layer. The fatigue tests were respectively carried out on the tooth of the gears with an oxidized layer and on the tooth of the gears without an oxidized layer. The fatigue crack was initiated from an oxidized layer on the specimens and gears with the oxidized layer. The oxidized layer played the role of a precrack. By considering the oxidized layer as a crack, an equation for estimating the fatigue strength of carburized steels with the oxidized layer was proposed. The parameters in this equation were the depth of the oxidized layer, surface hardness, and mean stress including residual stress. The fatigue crack was initiated from the surface of the tooth of the gears without the oxidized layer. The equation for estimating the fatigue strength of the carburized steels without the oxidized layer was also proposed. The parameters of this equation were surface hardness and mean stress including residual stress. Prediction accuracy was verified from these test results and other data. The fatigue strength of the specimens was estimated to be within 20% of the exprimental value, and the faigue strength of the gears was within 30%. Therefore, the prediction accuracy of the fatigue strength of the specimens was good.

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Delamination of a beam made from functionally graded material (FGM) is analyzed on the basis of classical beam theory. It is assumed that Young's modulus and the coefficient of thermal expansion vary continuously along the thickness direction, and the beam is subjected to the temperature distribution which also varies along the thickness direction. A general expression for the energy release rate of an edge delamination is derived based on so-called "cut and paste procedure". The analysis is then extended to an internal delamination that is parallel to the beam axis. It is shown that the analysis of the deflection of the beam is reduced to the solution of a nonlinear equation for axial forces acting in the beams above and below the delamination. The analyses are applied to a model FGM beam assumed by Erdogan, F. and Chiu, Tz-C [J. Thermal Stresses, Vol. 26, pp. 497-523 (2003)]. It is shown that both the deflection and the energy release rate compare well with those obtained by Erdogan and Chin based on finite element method.

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The creep damage condition of components under elevated temperature is a requirement to guarantee safe life extension and continued operation. Destructive and/or non-destructive assessments are regularly applied to assess the remaining life of components during service. Uniaxial creep specimens have been traditionally employed for conventional tests to examine a series of high temperature creep properties. However the ability to remove these relatively large uniaxial specimens is limited due to the required size of the specimens with respect to the component dimensions. To overcome this shortcoming, small element testing techniques such as miniature creep (MC) and small punch creep (SPC) tests have recently been proposed to investigate creep properties. However their application is limited as there is no established standard for the testing procedures and subsequent data evaluation. In order to aid the standardization of the SPC test method, this paper investigated the deformation and fracture of interrupted SPC tests. Results showed that the creep deformation in the SPC test could be classified into three conventional stages. Firstly, the crack of about 1mm in the diameter developed on the outer surface of the disc specimen at the end of the primary creep stage. Secondly, during secondary creep, circumferential cracking progressed in the through-thickness direction by about 0.1mm. Thirdly, the tertiary creep region was extremely short and only appeared just before final fracture and failure. The result showed that the ratio of load in the SPC test to stress in the uniaxial creep proposed past was smaller than the experiment value. This result was due to the early crack formation in the disc specimen and the shear type crack development.

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In this paper, the effect of magnetic field on fretting wear under gross slip was investigated in ranging number of cycles from 10^2 to 10^5 under the Hertz-type contact of steel ball to steel plate. The amount of fretting wear volume was evaluated by wear occurring on the surface of the steel plate with and without magnetic field. The experimental results show that the wear region spreads under the magnetic field and the worn volume is increased resulting from accumulation of the wear particles near contact tracks under the magnetic field. It is concluded that the wear particle trapped along the contact annulus increases the worn volume by abrasive and/or pile up action under magnetic field.

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To detect damage at possible stage is important in aerospace and other mechanical engineering industries. Damages in a structure change its dynamic behavior such as natural frequencies, damping and mode shapes. Vibration analysis of a beam is made to estimate the mode shape from measuring strain response under impulse loads. The analysis is illustrative of the validity of the mode shape from experimental strain response of a beam. As an experimental validation, cantilever beams with damage are tested. The damage is modeled as a notch. Continuous wavelet transform is applied to the mode shape which is estimated by strain response under impulse loads. Position of the damage is shown as a negative peak of the wavelet transform. The identified positions of damage are very close to the actual positions of damage except for existing damage near free edge of the beam.

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For residual life assessments of high-temperature parts of boilers, there are problems with accuracy in the late stages of service life, including Type IV damage. During our recent testing, it became clear that the cumulative strain on the surface has a high correlation to the burst life, but, we could not find a microminiature strain gage capable of making highly accurate measurements of strain. We developed the world's first microminiature slide capacitance-type high-temperature strain gage (φ3mm, 600℃ capable, accuracy within ±0.02% [±200μS], and strain range of at least 3%), and developed an on-line monitoring system at the same time. We created residual life assessment software that applied omega method and the Monkman-Grant method; achieved accuracy of approximately ±30%, which is three times that of conventional structural, ultrasonic, and other residual life assessment techniques (30-year history); and succeeded in the development of a revolutionary technique that enables highly accurate, constant observation.

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