Hydrogen embrittlement cracking caused at a weld joint is considered to be dominated by hydrogen diffusion and concentration driven by thermal stress induced by heat transfer during cooling process. The gradient of hydrostatic stress component is considered to be a driven force of hydrogen transportation. However, this problem concerns the occurrence phenomenon during cooling process. Therefore, diffusion coefficient, yield stress and Young’s modulus are changed corresponding with temperature change. Especially, diffusion coefficient shows the space gradient corresponding with space gradient of temperature caused by heat transfer. This affects the diffusion equation of hydrogen as a driven force of hydrogen diffusion. Under these backgrounds, to clarify not only the effect of local thermal stress but also that of space gradient of diffusion coefficient on hydrogen release and trap, the hydrogen diffusion analysis based on our proposed α multiplication and FEM-FDM methods was conducted by introducing the terms of gradients of diffusion coefficient and temperature into the diffusion equation. The following results were obtained. The space gradient of diffusion coefficient was found to contribute the release of hydrogen from the site of stress concentration when the gradient of local hydrogen concentration takes the same sign as that of diffusion coefficient. Concerning the prevention of hydrogen embrittlement cracking at weld joint, these results show that not only Pre-Heat Treatment (PHT) which is a mechanical factor, but also the space gradient of diffusion coefficient which is a factor of material science was found to be one of effective factor of release of hydrogen from a site of stress concentration.

Solubility of CaS in molten CaCl₂–65 mol%LiCl eutectic salt was examined by sampling of CaS saturated salt and ICP analysis. The handling in dried environment and an adequate mass of melt were applied for reliable measurements, in addition to suppression of inclusion of CaS particles. The solubility limit was found to be 0.22 ± 0.05, and 0.31 ± 0.05 mol%CaS at 873 K and 973 K, respectively. This saturation value was less than 1.77 ± 0.1 mol%CaS in pure CaCl₂ at 1173 K.

The range of application of molecular dynamics (MD) simulations is rapidly expanding owing to the recent advance in high-performance computing. Since only the coordinate and velocity of atoms in the system are directly obtained from MD simulations, it is important to correctly understand how the coordinate and velocity of atoms are converted into thermodynamic and interfacial properties. Here, MD-based techniques for estimating the thermodynamic and interfacial properties of metallic materials are assessed by considering practical examples of the melting point of a pure metal, the solidus and liquidus compositions of a binary alloy, the grain boundary energy, the solid-liquid energy, and the kinetic coefficient.

The transparent indenter which can used as an optical objective were tested to obtained a spectra during the indentation. A special device which comprises the transparent indenter and actuator was developed and embedded into the Raman spectrometer. An indentation into the silicon sample was performed and phases that exist under the load and without it were identified.

A spinal cage is one of the primary spinal devices used for the treatment of spinal diseases such as lumbar spondylolisthesis. Since it is set in the intervertebral space that causes instability to promote the fusion of the adjacent vertebral bodies, it requires the early induction of healthy bones. For this reason, in most cases, an autogenous bone extracted from the patient’s ilium is implanted in the interior of the cage to stimulate bone formation. However, collecting autogenous bone involves secondary surgery and several clinical problems such as pain in the part from which it is collected. Additionally, the effect of the autogenous bone graft itself has not been sufficiently studied yet. Moreover, the mechanical functions of trabecular bones in a vertebral body are governed by the anisotropic structure of the trabeculae and the preferential orientation of the apatite/collagen in a trabecula with respect to the principal stress. Despite this fact, after the implantation of the cage, the mass of the bones is evaluated with soft X-ray photography, which does not guarantee an accurate measurement of bone functions. In this study, the effect of the autogenous bone graft on the spinal cage was verified based on structural anisotropy of trabecular bones and the preferential orientation of apatite/collagen in a trabecula using sheep. The autogenous bone graft demonstrated a significant effect on the increase of bone mass and anisotropy of the trabecular structure. However, compared to the trabecular anisotropy of normal parts, the anisotropy of the trabecular structure and apatite c-axis orientation of the parts with autogenous bone graft were considerably lower, indicating a minimal effect of the autogenous bone graft. Therefore, it was suggested that early stabilization of the spinal cage requires another strategy that rapidly forms the unique hierarchical anisotropic structure of trabecular bones.