Strength of resistance spot welded lap joint is a very interesting task. JIS prescribes tensile shear test and cross tension test as a realistic environment in combined load. Then, a lot of strength prediction equations have been proposed. And these features are in the use of a threshold value based on the base material strength as a fracture condition. The relational expression between the cross tension strength and the opening angle deals only with the influence of the opening angle on the axial force acting geometrically on the base metal. But it explains the experimental results well. The strength of resistance spot welded lap joint in combined load is known to exhibit dependence of load angle. But it is not clear whether the cause is only the geometric influence as shown by the past equations or the fracture mechanism change depend on the load angle. In this study, we examined how much dependence of load angle can be explained by macro geometric factors using a material dynamics model, before studying the micro fracture mechanism depend on the load angle in the vicinity of the crack initiation part of the nugget. As a result, we were able to explain the dependence of load angle with the macro model.

Blood vessel exhibits a complicated microstructure depending on the anatomical portion, which enables the realization of its proper mechanical function. In particular, tunica media plays crucial roles in mediating the structural and functional properties of blood vessels. However, the microstructural analysis with quantitative methodology has not been established. In this study, the quantitative analysis of collagen fibers and elastin fibers in tunica media was achieved by combination of a selective staining technique using fluorescent dyes and birefringence measurement with polarized microscopy. The present method quantitatively unveiled the microstructural difference between thoracic aorta and caudal artery. Both types of vessels were comprised of collagen fibers and elastin fibers running along the circumferential direction of tunica media. Interestingly, the degree of preferential orientation of these fibers was markedly increased in thoracic aorta, suggesting that the anisotropic microstructure of vessel varies depending on the anatomical site.

We studied the fabrication of a TiO₂/SiO₂ composite coating on Ti. At a temperature above 1100 K with oxygen partial pressure, a self-organized coating of rutile phase TiO₂ is formed on a Ti substrate. The thick TiO₂ coating (> 10 m) had a “piecrust-like” multilayer structure, which comprise TiO₂ monolayers and gaps. A composite coating containing SiO₂ was fabricated via a sol-gel method in vacuum to improve the exfoliation strength of the brittle, porous TiO₂ coating. Cross-sectional SEM images revealed sufficient amounts of SiO₂ in the gaps between the TiO₂ monolayers in the TiO₂/SiO₂ composite coating, even at the interface between the oxide coating and the substrate. Exfoliation stress of the composite coating was up to 10–15 times higher than for the self-organized TiO₂ coating alone, and the composite coating’s failure mode was interfacial compared with cohesive for the self-organized TiO₂ coating.

Mater. Trans. 57（2016） 2008-2014に掲載

本研究の背景をより正確にするため，実験方法，結果，考察の一部を修正し，文献の追加および順番を変更，Fig. 12を追加した．

The solidification processes for Sn-2Ag alloy and Sn-2Ag-0.6Zn alloy have been directly observed in-situ using time-resolved X-ray imaging at SPring-8. In case of low cooling rate, the solidification condition is in coupled zone, the primary (β-Sn) has been overgrown by the eutectic structure. In case of other cooling conditions, the solidification of primary (β-Sn) dendrites and interdendritic eutectic structure have been observed. The dendrite tip radii have been characterized. It was found that the dendrite tip radius decreased as the growth velocity increased. The tip radius in Sn-2Ag-0.6Zn alloy is found to be smaller than that in Sn-2Ag alloy, when the growth velocity is the same. The values of tip radius agreed well with the previous results which were obtained using the unidirectional solidification and quenching technique.