In order to establish a principle for suppressing the functional fatigue of shape memory alloys, we are investigating the geometrical condition of the martensite microstructure consisting only of the compatible interfaces, and the relationship between deviation from the geometric condition and the functional fatigue. We give an overview of the previous researches on how to understand the martensite microstructure based on the geometry of deformation, and the basic concepts to suppress the accumulation of dislocations upon cyclic actuation of shape memory alloys. Finally, we introduce the Triplet Condition (TC), a new condition of supercompatibility between martensitic variants, formulated by the authors and discuss the potential of TC for a design principle of durable shape memory alloy.
It is well known that light environment affects the mechanical properties of inorganic semiconductor materials, but still little is understood about the detailed mechanism. We before reported that single-crystalline zinc sulfide, an inorganic semiconductor material, exhibits significant plasticity in the dark. This finding has prompted us to investigate the effect of light environment on the dislocation behavior of inorganic semiconductor materials once again. On the other hand, in understanding the effects of light environment on dislocation behavior, it is difficult to obtain large, millimeter-sized crystals of advanced inorganic semiconductor materials to which conventional mechanical tests can be applied. Therefore, one of the main goals of our research project is to establish a method to understand dislocation behavior at the nanoscale by constructing a new nanoscale mechanical testing system that can be applied to thin substrates under controlled light environment. We have successfully constructed a new nanoindentation system (we call Photoindentation) in which light can be quantitatively applied below the indenter from two directions at the same time, and conducted creep tests in which a constant load is applied at or above the load at which dislocations occur (pop-in stress). In addition, care was taken to obtain statistically correct experimental results by conducting a great number of experiments. As a result, it was demonstrated that light has little effect on the nucleation of dislocations, while light has a strong effect on the glide motion of dislocations. In addition to these nanoscale experiments, macroscale experiments have been conducted in an effort to further understanding of light environment effects on dislocation behavior.
In this paper, a stress concentration around two holes of a 3D-printed material and stress intensity factors (SIFs) at straight crack tips of a rock are shown graphically as several practical calculation examples. The stress components and SIFs are calculated using the two-dimensional elastic theory. The elastic constitutive equation of materials has been used as isotropy or orthotropy in most previous analyses. Consequently, the mutual influence of the in-plane and out-of-plane shear problem has rarely been discussed. Therefore, at the first in this paper, the solutions that take into consideration the general constitutive equation with such mutual influence, are derived by the modified Lekhnitskii formulation. Next, numerical calculations for a 3D-printed polycarbonate plate subjected to uniform tension are performed in order to evaluate the mutual influence of anisotropy on the stress concentration for two circular holes. By changing the distance between the holes and angle formed by the stack and tensile directions, not only the effect of these parameters on the magnitude of out-of-plane shear stress but also the stress concentration factor for tension are clarified. Further, SIF for fracture mode I is calculated for a straight crack group in granite, and the mutual influence of SIF for fracture mode III is evaluated. As the results, it is found about SIF for fracture mode III that it becomes zero for enough crack spacing, whereas it is increasing continuously with increase of crack density.
In this study, unidirectional compression creep tests were performed on seven types of commercial optical glasses with different chemical compositions to investigate the effect of chemical composition or network structure on stress relaxation behavior. As a result of comparing stress relaxation rates obtained by dividing the shear relaxation modulus by the shear instantaneous modulus, they showed almost the same shape on the logarithmic time axis. In other words, it was clarified that the chemical composition has almost no effect on the stress relaxation behavior, at least in the glasses used in this study. On the other hand, it was confirmed that the difference in chemical composition affects the relaxation time, and the relaxation time of the chain structure glass tends to be delayed compared to that of the three-dimensional network structure glass. Furthermore, the activation energy of viscous flow obtained by approximating the shift factor also tended to be slightly lower in the chain structure glass.
In this study, the surface of industrial pure iron was treated with atmospheric-controlled induction heating fine particle peening (AIH-FPP) using mechanical coating (MC) particles of carbon/steel obtained by mixing carbon powder and fine steel particles using mechanical milling. The surface modification effect and the mechanism of its effect were examined and considered by analyzing of the treated surface. Results showed that a modified layer in which carbon elements were diffused was formed near the treated surface by the AIH-FPP treatment using MC particles. In addition, by examining the influence of the treatment conditions on the formation of the modified layer by the design of experiments, the treatment temperature showed the most significant influence among the treatment temperature, peening time, and gas flow rate. The higher the treatment temperature, the deeper the carbon diffused layer. In addition, when treated at ≥1273 K, the microstructure near the surface became pearlite, and Vickers hardness increased. The time required for carbon diffusion in the AIH-FPP carburizing process using MC particles of carbon/steel was approximately the same as that of a general carburizing treatment using a reactive gas. In the AIH-FPP carburizing process, carbon is considered to be transferred from the particles to the surface, and the grain boundaries and dislocations increased by fine particle preening (FPP) are used as channels to diffuse inside the specimen. This mechanism is entirely different from the conventional carburizing methods.
Steel corrosion in concrete structures adversely influences safety performance and durability. This study proposes a giant magnetoresistance (GMR) sensor-based eddy current nondestructive testing method to detect the decreasing steel area caused by corrosion under a 30 mm thick concrete cover. The 30 mm lift-off distance is a big challenge that many eddy current testing (ECT) methods can only perform with a lift-off distance of a few millimeters. As a primary step, artificial cutting flaws on the SPCC steel plate surfaces were used to simulate the material loss by corrosion. The GMR sensor-based eddy current detection probe succeeded in obtaining stable voltage data with a 30 mm lift-off distance by scanning perpendicular to the flaws, and the shape of the voltage amplitude with its gradient values was found to be effective in determining the flaw’s existence and position. The finite element simulation and experimental results verified the validity and feasibility of this method. Finally, the XY-direction scan was performed to provide 3D images to visualize the flaw location.