This study presents a simple interatomic bonding model for disordered A2 and B2 crystal structure. The model consists of an atom-like sphere and eight polar bars attached to its surface. Every bar has a polarity and can only attract a bar of the opposite polarity. Each bar is oriented from the surface of the sphere to a vertex of the cube, of which the sphere is placed in the center. A motif is defined as a combination of polarities on the eight bars, the total of which is 256 although a number of them are identical after rotation and/or inversion. Only 13 motifs classified by point groups are found to be unique by point symmetrical operations. In addition, an A2-like crystal structure is formed by connecting the bars between the models and filling the space. Four bonding patterns are found to configure the space of models with unique motifs according to symmetrical operations between the motifs of the center and neighbor atoms. Each crystal structure includes several kinds of point symmetry, and each shape memory binary alloy (SMBA) can be connected to the motifs on the atomic model via crystal structure and point symmetry. The results reveal the potential structure of the electron population distribution of each element in an SMBA that could be compared with ab initio calculations.

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This work presented new developments in the constitutive modeling of shape memory alloys (SMAs). As an increasing number of experimental results are being published, it is becoming increasingly difficult to describe complicated SMA behaviors using conventional models. To overcome the shortcomings of existing models, this research proposed two major improvements to the assumed phase transformation function. A more flexible function called logistic sigmoid function has been introduced into the phase transformation function. This improvement affords a better fit to the typical SMA stress-strain relationship. Moreover, a cyclic effect has been considered while developing the new model. The new model is proposed by connecting accumulated strain with the critical phase transformation constants of SMAs. Both improvements were first validated at the material level. Thereafter, structural level validation and application were conducted. Accuracy enhancement may be expected by adopting these new models in SMA-related simulations.

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Among many functional structures, the low shear stiffness type shape memory alloy (SMA) honeycomb structure is considered as an ideal candidate for actuator, sensor, and shape control devices. This work extends conventional SMA computational models with essential functions such as consideration of twinned martensite, support for plastic deformation, and enhancement for hysteresis behavior model. Using these improved models, we conducted numerical studies related to low shear stiffness type SMA honeycomb structures. Fundamental studies related to tensile and compressive loading behavior were conducted first, followed by simulation of the honeycomb core actuator considering simultaneous changes in temperature and stress level. In the field of simulation, this is the first comprehensive study related to SMA honeycomb structures. Both model validation and new discoveries could be expected from this work.

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A creviced bent beam (CBB) test was performed on Type 316L stainless steels with work-hardened surface layers in high-temperature water at 561 K. Growth process of the oxide films on the surface was investigated by cross-sectional transmission electron microscope observation. The oxide films were found to consist of an inner Cr-rich layer and an outer layer of Fe₃O₄ particles. The crystal structure of the inner layer changed from a face center cubic to a spinel-type with an increase in CBB test duration. The inner layers showed a cube-on-cube orientation relationship with adjacent austenite grains of the substrates.

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For the stabilization of insulation performance in resin-molded insulators, strong adhesion between the resin and metal is required. In this paper, the influence of surface roughness on the interfacial strength between the resin and metal was investigated. Test pieces were made by covering Cu and SUS cylinders, which had varying for surface roughness, with epoxy resin. The interfacial strength was evaluated with shearing tests on these test pieces. The effective adhesive surfaces of those cylinders were evaluated from surface observation with a laser microscope. The interfacial strength increased with surface roughness. The adhesion-strength index (µ+B), which was proposed in our previous paper, was calculated with the effective adhesive surface and the interfacial strength. The adhesion-strength index gave a constant value with various surface roughnesses for each metal.

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The analytical solution of an infinite plate with a circular hole is introduced for investigating algorithm errors in identification of material parameters instead of performing actual experiments. The simulated speckle image pairs, consisting of undeformed images and deformed images, are created from analytical function. Then, a new formulation of digital image correlation (DIC) based on optical flow and finite element methods is developed to estimate heterogeneous displacement fields from simulated speckle images. The compliance coefficients of testing materials are iteratively computed by comparing finite element strains to DIC strains. The isotropic and orthotropic models of material parameters are investigated for accuracy of the purposed algorithms. The interaction between algorithm errors is studied. The sources of errors are discussed and progressive improvement is suggested for these identification techniques.

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The changes in the microstructures associated with plastic deformation and strain/stress were measured using the strain scanning method with hard synchrotron radiation. Aluminum single crystals tensile-deformed along the <111> direction exhibit a macroscopically uniform multiple-slip without deformation bands. Plastic deformation has an insignificant effect on lattice spacing, and is likely responsible for the relatively uniform distribution of internal stress with a small absolute value. With regard to the crystallographic orientation, the rocking curves in the as-annealed sample differed with position, strongly suggesting that mosaic structures exist in a single crystal. In the 8% tensile-deformed sample, mosaic blocks are divided into smaller size. The increase in the number of mosaic blocks with deformation causes broadening the rocking curve and FWHM of the profile.

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The interaction between Euler buckling and Brazier instability in an orthotropic cylindrical tube was investigated. A simple closed-form interaction curve was obtained by using the principle of minimum potential energy including the 3D extended Brazier's 2D type cross-section ovalization and the potential energy of axial compression. The interaction curve consists of an Euler buckling load and a bending instability load, which slightly differs from Brazier's bending instability load. Hence, the differences between these bending instability loads were also investigated. The interaction curve was validated by comparing it with the finite element analysis results from the open literature, and it was confirmed that it gives good estimates.

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The energy absorbing ability of a crashworthy structure for a railway's rolling stock composed of welded aluminum alloys was evaluated numerically using finite element analysis (FEA). In the numerical simulation, two different material models were employed to characterize the base aluminum alloys and welding materials: one was a damage-mechanics model and the other a conventional plastic-mechanics model. The energy absorbing abilities of two different types of crashworthy structures were predicted using the FE simulations, and the numerical predictions were compared with experimental results obtained from quasi-static compression tests using mockups of these two crashworthy structures. The local phenomena (buckling and fractures) observed in the mockup tests, were also predicted numerically. The local fractures were accurately reproduced in the FE simulation employing the damage-mechanics model, while the buckling behaviors were predicted with substantial accuracy in both simulations. Comparison of the experimental results and the numerical predictions also revealed that the FE simulation applying the damage-mechanics model had an advantage in accurately predicting the energy absorption. The relationship between the local phenomena and the structural energy absorption is discussed.

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Our previous study has demonstrated that Ni and Ge microelements-added Sn1Ag0.5Cu0.07Ni0.01Ge (SACNG) solder showed a higher electromigration (EM) resistance than Sn1Ag0.5Cu (SAC) solder. However, it is not yet clear whether enhancing the EM resistance of SAC solder is taken by both of Ni and Ge microelements, or taken by single Ni or Ge microelement. This paper investigates the respective effect of single Ni and Ge microelements on the EM resistance of SAC solder. The EM resistances of Sn1Ag0.5Cu0.07Ni and Sn1Ag0.5Cu0.01Ge solders are experimentally compared via the morphological change, which is quantitatively investigated by measuring the ratio of the total EM-induced hillock volume to the time for current supply in a certain area in a sample. The experimental conditions are same as those used for SAC and SACNG solders in our previous study, and the result is analyzed together with the two reported solders mentioned above. It is concluded that single Ni and Ge microelements separately enhance the EM resistance of SAC solder, and adding of both Ni and Ge microelements together further enhances it. A possible mechanism is proposed to explain the investigated effects.

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