Effect of prestrain of fatigue crack initiation and propagation in SiCp/Al2024 composites
Akiniwa Yoshiaki; Tanaka Keisuke; Shimizu Kenichi; Hagiwara Takaaki
Abstract:The effect of prestrain on the fatigue crack initiation and propagation behavior of an aluminum alloy (2024-T6) reinforced with 20 volume percent of SiC particles was investigated. Cracks were mainly nucleated in the matrix by prestrain of about 0.32% strain. The X-ray diffraction method was used to measure the change of residual stress in the SiC particles and in the matrix before and after prestrain. The residual stress changed from -134 to -107MPa in the SiC phase and from 0.6 to -12MPa in the matrix phase. Fatigue tests were conducted using a specially designed servo hydraulic fatigue testing machine in a scanning electron microscope. The initiation and propagation behavior of small fatigue cracks in a smooth specimen was observed. Fatigue cracks were mainly nucleated from the matrix cracking and propagated in the matrix near the particles. When compared at the same maximum stress intensity factor, Kmax, the crack propagation rate, dc/dN, of the prestrained material was higher than that of the non prestrained material because of the damage near the interface. Key Words:fatigue, metal matrix composite, particle, SiC, prestrain, in situ observation