Role of Crack-Tip Residual Stresses in Stress Corrosion Behavior of Pre-stressing AA7020

Abstract

This paper analyzes stress corrosion cracking (SCC) of pre-cracked samples in the presence of compressive residual stresses generated in the vicinity of the crack tip during fatigue pre-cracking. Research focuses on the role of crack-tip residual stresses of compressive nature, generated by fatigue loading, in stress corrosion cracking of pre-cracked samples of medium high strength aluminum alloy 7020 subjected to localized anodic dissolution and hydrogen assisted cracking. Fatigue pre-cracking load on the samples generates compressive residual stresses in the vicinity of the crack tip which improve the stress corrosion behavior of the aluminum alloy by delaying either the metal dissolution or the hydrogen entry, thus increasing the fracture load in an aggressive environment. The rice model of the residual stress distribution in the vicinity of a crack tip may be used to explain these retardation effects by estimating the stress level and plastic zone size. Microscopically, compressive residual stress produces a transition topography between the fatigue pre-crack and the cleavage-like (unstable) fracture mode.