Shape memory alloys (SMA) exhibit superelastic behaviors and shape memory effects accompanied by austenite and martensite transformations. Computational tool is useful to design SMA-based devices efficiently. Brinson's one-dimensional constitutive modeling for SMA is extended to take into account the asymmetric tensile and compressive stress-strain behavior and applied to the finite element analysis of simple SMA devices in this paper. The superelastic behaviors of a bar subjected to tension as well as a supported beam subjected to four-point bending are analyzed under the assumption of small deformation. The calculated results for the beam agree well with the experimental results in the literature.

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The use of shape memory alloys has been growing in recent years. It is expected that computational tool will be used more widely in the design of SMA-based devices. In this paper, Brinson's one-dimensional constitutive modeling for SMA is extended to take into account torsional behavior. The incremental finite element method is formulated by the total Lagrangian approach for finite deformation problems. The superelastic behavior of a bar under torsion is analyzed and the calculated results are compared with the experimental results. A helical spring is also analyzed to show the validity of the present computational procedure in actual design of SMA actuators.

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This paper presents a dual reciprocity boundary element method (DRBEM) applied to the transient heat conduction problem of functionally graded materials. The functionally graded material can be modeled as an inhomogeneous one where the thermal conductivity is a continuous function of coordinates. The integral equation formulation employs the fundamental solution of Laplace equation for homogeneous materials, and hence from the inhomogeneous part of the governing differential equation a domain integral arises in the boundary integral equation. This domain integral is transformed into boundary integrals by using a new set of radial basis functions. Furthermore, time derivative is approximated by the time-stepping method, and the domain integral also appears from this approximation. The domain integral concerning the "pseudo" initial condition at each time step is also transformed into boundary integral via the same dual reciprocity method. The details of the proposed DRBEM are presented, and a computer code is developed for two dimensional problems. Through comparison of the results obtained by the computer code with the result of collocation method, the usefulness of the present DRBEM is demonstrated.

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Mechanical properties and deformation mechanisms of nanopolycrystalline (NPC) materials under tensile test are studied by using molecular dynamics. An embedded atom mehod (EAM by Mishin, et al. 1999) and an effective medium theory (EMT by Jacobsen, et al. 1987) are adopted as the interatomic potentials of Al to investigate the influence of stacking fault energy (SFE) on the phenomena, for the typical difference of them is that the latter underestimates the SFE of Al. Simulations using 3 different models are carried out to study the dependence of grain size under different strain rate conditions. For all cases, the dependency of maximum stress on grain size can be expressed as an inverse Hall-Petch relation. This tendency is considered and may be directly explained by volume effect of grain boundary (GB). Both crystal slips and GB slidings are observed, but the GB sliding is predominant in small grain model. The most crystal slip is motion of perfect dislocation in the EAM potential cases, but in the EMT potential cases the most crystal slip is caused by motion of Shockley's partial dislocation. Because the EMT potential underestimates the SFE, the core length of the extended dislocation is comparable to the grain size and there remains a lot of stacking fault in grains. During the unique deformation process by partial dislocation movement, a strange rotation of grain is also observed. It is to say that the deformation mechanism of NPC materials is strongly influenced by the SFE. As another interesting deformation mechanism, the grain switching process is observed. In the macroscopic viewpoint, this is quite similar to the switching mechanism proposed by Ashby and Verrall (1973). But, there is a significant difference; in the present study both the GB migration and sliding are predominant but Ashby and Verrall's model is based on diffusion contrarily.

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In this paper, the two types of the reliability-based design of a laminated composite plate subject to in-plane loads are formulated in terms of lamination parameters to improve the calculation efficiency. One is the reliability-maximized design of the constant-thickness plate. The other is the thickness-minimized design under the reliability constraint. The first ply failure (FPF) criterion is adopted as the plate failure, so that the laminated plate system is modeled as a series system consisting of each ply failure. The ply reliability is evaluated by the first order reliability method (FORM), where the material properties and applied loads are treated as random variables. Then, the system reliability is approximated by Ditlevsens bounds. Through numerical calculations, it is demonstrated that the reliability is distributed smoothly in the lamination parameter space and that a quick convergence is achieved in the reliability-based optimization.

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Rotating bending fatigue tests were carried out for 18% Ni maraging steel in order to investigate the influence of reversion austenite on notch sensitivity of maraging steel. Fatigue strength was increased by formation of reversion austenite. The increase in the fatigue strength was large near the fatigue limit. In the range of notch radius ρ larger than 0.05 mm, fatigue limit was determined by the limit for crack initiation in the material without reversion austenite, whereas a non-propagating crack was observed in only the notched specimen of ρ=0.05 mm in the material formed reversion austenite. These were caused by suppressions of the crack initiation and its early propagation due to formation of reversion austenite. However, the influence of reversion austenite on notch sensitivity was very small.

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In this study, high temperature fatigue crack propagation test of the engineering plastic material was carried out in order to clarify the effect of loading rate on the fatigue crack propagation property at the high temperature environment above Tg. Then, failure mechanism and loading rate dependence were evaluated. (1) The resistance against the crack propagation at 30 Hz that was high loading rate was more excellent than that at 10 Hz and 3 Hz which was low-loading rate. And, the resistance against the crack propagation at 10 Hz was equivalent to that at 3 Hz. (2) The resistance against the crack propagation of R 1 material remarkably decreased in comparison with that of virgin material. However, the resistance against the crack propagation of R 3 material was almost equal to that of R 1 material. (3) From the fractography using SEM the fracture surface at high loading rate was a brritle form, and the effect by the fatigue was big. In the meantime, that at low loading rate was a ductile form, and it seemed to overlap fatigue and creep. The viscoelastic effect of the matrix seems to remarkably appear in the fracture surface at low loading rate. (4) It was proven that the process zone dimension and the reinforced fiber length influenced the difference between fatigue crack proagation mechanism at the high loading rate and that at the low loading rate.

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In this paper, to verify the applicability of the viscoplastic constitutive model, which was previously proposed by the authors, to the viscoplastic deformation at the high temperatures, a series of tests such as cyclic tension-compression loading with the constant strain amplitude under the constant strain rate and creep tests are carried out at the high temperatures by using oxygen-free copper (OFC). A cyclic tension-compression tests under variations of temperature is also conducted. The experimental results show that the temperature history does not affect stress-strain relations under cyclic tension-compression loading regardless of variations of temperature. Using the material constants determined by the cyclic tension-compression test at isothermal condition, creep and cyclic deformations under variations of temperature can be well simulated by the viscoplastic model.

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Depending on casting methods, aluminum alloy cylinder heads differ greatly in quality and local strength as well as overall strength. Obviously, casting methods largely affect the durability of a cylinder head. Therefore, in order to precisely evaluate the durability of a newly-designed cylinder head by CAE, it is necessary to introduce a new method with the effects of a casting method taken into account. In our research, a method has been devised to be used in CAE in such processes from engineering to manufacturing for evaluation, More specifically, by using the method, metallurgical microstructure of cast aluminum alloy is analyzed by dividing cylinder head into such domains as lower deck, middle and upper deck parts for mechanical properties and a casting defect of porosity. The domain profile information on mechanical properties and porosity has helped us improve accuracy in the structural analysis.

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In the previous paper, we presented an axisymmetric solution for the stresses and displacements in an elastic thick plate containing an oblate spheroidal inclusion under axisymmetric bending around the z axis normal to the surface of the thick plate. In the present paper, we studied an asymmetric solution for an elastic thick plate containing an oblate spheroidal inclusion under transverse bending. Numerical results are given for different values of size, aspect ratio and stiffness ratio. The stress distributions around inclusion are shown graphically, and are compared with the axisymmetric results.

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It is desired to obtain the material properties in a wide range of strain rates and strain to be used for numerical simulations of car crushing, high speed forming and others. To conduct dynamic material testing, adapting suitable specimen size and shape for each testing strain rate is important to obtain the results with good accuracy and interchangeability for a wide range of strain rates. Any standard for the specimen size and shape, however, is not yet established except quasistatic testing. In this study, the upper limit of the gauge length of the test piece, to keep the testing error under a few percent, for the dynamic tensile testing in the strain-rate range from 10² to 10⁴ s^-1 were obtained through a series of numerical simulations.

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In recent years, an increasing interest has been paid to the accurate measurement of stress-strain relations of materials for wide range of strain rates which are needed to formulate the constitutive equations of rate-sensitive materials precisely. The Hopkinson Pressure Bar system is widely used for this purpose. However, the device should be long enough to prevent the immediate reflection of stress waves from the ends of the input and output bars. The newly developed Sensing Block (SB) system, which consists of a small sensing projection and a relatively large mass block, is expected to be used widely for many materials. In this paper, the bounds of application of the SB method for measuring dynamic load was examined numerically. The relation between the size of sensing projection and the rising time of applied load was cleared to satisfy some criterions on the accuracy for each model. The results ensure the sufficient accuracy for measuring dynamic load under the obtained conditions.

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A new impact testing machine was proposed, which was possible for various two stage impact loading tests of tension and torsion. Especially, the testing machine can realize the impact loading and inverse loading in order to examine the Bauschinnger effect at high strain rates. This machine is based on SHPB method, and has two clamp devices that are released in the time lag of 100 μs by connecting the two clamps to a rod. Using the testing machine, some efficiency tests were done. The results showed that the rise time of the impact load is about 50 μs and the present machine is valid as an impact testing machine. Moreover, some impact experiments were conducted with short aluminum specimens. It was confirmed that the Bauschinnger effect appeared under the impact loading as same as the static loading.

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An X-ray analytical microscope (XAM) has been applied to evaluate environmental degradation of FRP. In the XAM examination, a parallel beam geometry has been used with a 10 micrometer and a 100 micrometer diameter X-ray guide tube and a high-purity silicon X-ray detector. The X-Y scanning stage, which has a 100 mm of travel distance, allows us to examine samples in the air. Therefore large sections or several samples can be examined simultaneously. Using the XAM, the area of interest can be analyzed and the compositional image of the sample is obtained. The sample is FRP immersed in an acid solution. The penetration of the acid into the sample was analyzed after the immersion by the XAM. It has been indicated that the XAM technique is particularly useful for the analysis of the elemental distribution in an organic matrix such as FRP.

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The compressive deformation properties of polyurethane-shape memory polymer foam depending on time were investigated experimentally. The results obtained are summarized as follows. (1) The compressive deformation of the foam initiates at a certain local part and progresses from that part. During the unloading process, the shape recovery starts from the part which is deformed at the end of the loading process. (2) Creep deformation is large if the initial deformation is small. Both creep strain and creep recovery strain are large at temperatures below the glass transition temperature T_g. (3) Relaxed stress after a certain time is proportional to initial stress. The ratio of stress relaxation is large below T_g but is small above T_g. (4) The amount of stress relaxation is large if strain rate is high during the loading process. (5) If large strain is applied, followed by keeping the stress constant above T_g, irrecoverable strain appears. If large strain is kept constant above T_g, stress almost relaxes and the strain is fixed.

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The experiment was conducted on the compact normal and shear (CNS) specimen made of acrylic resin subjected to various kinds of mixed-mode loading. The 2-D hybrid method proposed by Nishioka et al. was employed to evaluate the 2-D stress field from displacement data obtained by the experiment. Moreover, the 3-D hybrid method was applied to evaluate the 3-D stress field from displacement data obtained by the experiment. Also, a 3-D finite element analysis was conducted on the same specimen as the experiment. An embedded speckle photography can estimate stress intensity factors of mixed mode. The 3-D hybrid method can evaluate the stress field inside the specimen from displacement data at the free surface taken in easy measurement by speckle photography.

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This paper describes a newly developed arrayed multi-coil probe for the testing of steam generator tubes by eddy current testing. Owing to the multi-coil arrangement, it is possible to detect cracks in the whole round of the tube without rotation. Geometry of the probe was decided with the help of numerical simulation, which leads to high detectability of the probe. The signals of this probe were predicted by the edge based finite element method, and comparison between experimental and numerical results showed good agreement. Furthermore, this probe is expected to be convenient to reconstruct the crack shape from its C-scan image.

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