The effect of mean stress on fatigue crack propagation in half-inch (12.7 mm) thick specimens of aluminium alloys of high and low fracture toughness

Abstract

Experiments have been made to investigate the effect of mean stress on fatigue crack propagation in 1 2 in. (12.7 mm) thick specimens of six aluminium alloys of high and low fracture toughness. The results are presented in terms of the stress intensity factor range, ΔK and the R value where R is the ratio of minimum to maximum stress. It was found that increasing R had little effect on the fatigue crack propagation rate for the alloy of very high fracture toughness ( L64) but that for the other alloys the rate increased rapidly with increasing R at high values of ΔK. A simple law is proposed relating the fatigue crack propagation rate to ΔK, the R value and the fracture toughness of the material.