Host: The Japan Society of Mechanical Engineers
Name : [in Japanese]
Date : November 02, 2019 - November 04, 2019
In recent years, MEMS technology has been used to develop various micro sensors and electronic devices.Nickel thin films have been mainly used as structural materials for MEMS devices made by the LIGA process. By reducing the crystal size of nickel thin films to the nanoscale, the fatigue strength of the thin film is improved. However, the fatigue strength may become more sensitive to stress concentration such as surface and internal defects and cracks. In this study, the influence of micro-notch shape on fatigue strength was studied using electrodeposited nickel thin films with nanocrystal grain (NCG) of 16.5 nm in grain size. NCG thin film has two types of micro notch-tip shapesintroduced by FIB processing. One issquare type with both corners at the notch tip (MN type) and the other is circular type with curvature at the tip (MNR type). Fatigue strength decreased with increasing notch depth. The fatigue strength decreased as the radius of curvature of the notch tip became sharper. The fatigue limit is controlled by the initiation of fatigue cracks. The effect of the notch shape on the fatigue limit of MNR type micro-notch specimens is predicted by the fictitious-crack model.
