Effect of loading frequency on fatigue crack growth between a submicron-thick film and a substrate

Abstract

The crack growth along the interface between a submicron-thick film (Cu) and a substrate (Si) under fatigue is experimentally investigated at the load-frequencies of 0.1 Hz and 1 Hz in a laboratory environment (45 ± 5% RH). A modified four-point bend specimen, which has only one interface crack to facilitate the control of crack growth, is used for the tests. The results reveal that the clear interface crack between Cu and Si grows under the cyclic load. The crack growth rate per cycle, da/ dN, is governed by the stress intensity factor range, ΔKi, at each frequency and the sigmoidal relationship consisting of three stages are observed in the da/dN - ΔKi curve; the threshold, the stable growth and the critical growth. da/dN greatly increases as the frequency decreases in the stable growth region. The crack growth rate per time, da/dt, shows a good correlation with the maximum stress intensity factor, Kimax, independently of the loading frequency. This indicates that the environmental effect due to humidity in air plays a dominant role on the crack growth.