Damage evolution model under tension–compression axial loading using a nonlinear constitutive theory: A high-cycle fatigue study on cast AS7GU-T64 alloy

In this work, we performed extensive high-cycle fatigue testing of AS7GU-T64 cast aluminum alloy, which is primarily used as cylinder heads in automobiles, under load-controlled, axial tension–compression to understand its damage evolution. We begin with a small-strain finite deformation theory to derive a nonlinear constitutive relation. This relationship is shown to be a fourth-degree expression and not a general power series. The constitutive relations are then used to develop a damage metric, which captures the asymmetry in tension–compression responses. The metric measures the damage as a ratio of nonlinear to linear terms in a stress–strain behavior, signifying the deviation from linearity to nonlinearity. The cyclic loading–unloading response is measured through a least squares fit to the data. The measured fatigue data is demonstrated to very effectively capture the evolving damage prior to catastrophic fracture. Finally, we present the postfailure analysis of the fractured samples.