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One way of addressing environmental problems is to increase the use of light-weight materials in automobiles, such as the multi-material structure, which improves fuel economy and reduces pollution. However, it is necessary to develop a welding technique to join carbon fibre-reinforced plastic to metals to achieve a multi-material structure. So, this paper aims to shorten the welding time and to clarify the fatigue fracture mechanism of shear type friction stir spot welding joint between aluminium alloy and CFRP experimentally and analytically. As a result, the static and fatigue strength of the joint improved as the welding time increased due to the increase of total joint area to increased resin melting.

With the rapid development of computer‐aided design/computer‐aided manufacturing (CAD/CAM) systems, the application of zirconia in removable partial dentures is expected to expand. Clasps composed of zirconia should improve esthetics without inducing the risk of metal allergy. The aim of this study was to examine the fatigue resistance of yttria‐stabilized tetragonal zirconia polycrystal (Y‐TZP) clasps for removable partial dentures. Yttria‐stabilized tetragonal zirconia polycrystal and cobalt‐chromium (Co‐Cr) alloy were prepared using CAD/CAM systems. Specimens were either of the semicircular type or of the flat type, with cross‐sectional areas of taper ratios of 0.50, 0.75, and 1.00. All specimens were tested using the cantilever test and the constant displacement fatigue test, and data were analyzed using ANOVA. During the cantilever test, the maximum displacement prior to fracture was greater than the required undercut, and the semicircular‐type specimen exhibited a higher fracture load than the flat type. None of the specimens displayed permanent deformation and showed almost the same degree of deformation after fatigue testing. A lower taper ratio was associated with lower average load values and greater displacement. Within the limitations of this study, it was possible to conclude that Y‐TZP provides the required undercut and adequate retentive force for removable partial denture clasps. Additionally, Y‐TZP and Co‐Cr alloy had almost the same degree of deformation even after the simulated lifespan of removable partial dentures.