The study of fatigue behavior of countersunk fastener holes

摘要

In this paper,a series of fatigue tests have been carried out using reverse double dog bone specimens containing countersunk fastener holes. The material of specimen is aluminum alloy 7050. During fatigue tests,two types of block spectrum loads are used to obtain the relationship between the crack length and fatigue life. For two block spectrum loads that used,the max stresses are same and the stress ratios are 0.06 and 0.53 respectively. Fracture surfaces of the specimens are observed by optical microscope to disclose the mechanism of fatigue failure. Finite element method (FEM) is used to analyze the distribution of stresses around the countersunk holes of specimen when load applied. The results reveal that fatigue cracks always initiate at location where the max stress occurred at. The mechanism of crack initiation is that crack is induced by stress concentration. Crack initiation life is about 80% of total fatigue life of fastener holes. The fatigue life of fastener holes is monotone decreasing when applied load increase. But the dispersibility of fatigue life of fastener holes is not monotonic varying with increasing of applied load.