Random fatigue crack growth in aluminum alloys

Abstract

Multi-crack panel type aluminum specimens were tested under constant amplitude loading, constant amplitude with superimposed overloads loading and random variable amplitude load history. A numerical procedure of real-time generation of a truncated and condensed random load history corresponding to a given power spectral density was developed. The cracks growing in the same multi-crack specimen had close fatigue crack life both under constant amplitude loading and random load history. The crack growth rate exponent of the Paris law had small variation and was treated as a constant value. The C-coefficient variation did not exceed 4% under constant amplitude loading and 3% under random load history. The crack growth rate exponent in 2024-T3 aluminum specimens under constant amplitude loading was equal to 3.76, whereas under random load history it decreased to 2.03. This decrease is due to greater retardation effect of the overloads in the random loads ensemble when all the loads proportionally increase with growing cracks.