Assessing notch fatigue performance of aluminium alloy AA2024-T4 after uni-axial and equi-biaxial tensile pre-straining: Experimental observations and predictive models

Abstract

This study delves into the effect of different tensile pre-straining (uni-axial and equi-biaxial pre-strain) modes on the notch fatigue performance of AA2024-T4. By conducting a series of fully reversed stress-controlled high cycle fatigue (HCF) experiments, pre-strained samples demonstrated notable improvements in HCF resistance, surpassing those without pre-strain. A stress-based fatigue life prediction approach, namely the theory of critical distance (TCD), is applied. We propose an experimentally validated physics-based method for predicting notch fatigue life in the HCF regime, utilising the cyclic plastic zone (CPZ) concept and TCD’s point method. The CPZ commonly plays a significant role in both crack initiation and propagation at the notch roots, thereby altering the stress in the vicinity under cyclic loading. However, TCD considers a linear-elastic stress field around the notch root for fatigue life calculation. The model successfully predicts HCF life based on experimental results and gives better prediction than the conventional TCD approach in terms of prediction accuracy, which falls within a range of ± 2 the experimental results for all the pre-strain conditions.