DICを用いた電着ニッケル薄膜の疲労き裂進展に及ぼすき裂開閉口の影響

抄録

Two types of nickel thin films with grain sizes of 384nm(UFG : Ultra Fine Grain) and 17nm(NCG : Nano Crystalline Grain) were created by electrodeposition using a nickel sulfamate bath. Nickel thin film of 10μm thickness was adhered to a through elliptical hole in a base plate and was fatigued in accordance with the displacement constraint along the hole circumference in the base plate subjected to a cyclic stress. Commonly, a stress intensity factor range was increased with a crack propagation under a constant stress amplitude but was decreased toward the hole edge because of the difference in thickness between the film and the base plate in this ΔK-decreasing test method. As a result, the figure crack propagation rate da/dN, is higher for NCG than for UFG in the relationship between the da/dN and stress intensity factor range, ΔK. The crack opening stress was evaluated by DIC(Digital Image Correlation) method and effective stress intensity factor, ΔK_eff was estimated. Relationships between da/dN and ΔK_eff are almost equal UFG and NCG.