Modeling procedure for the damage-accumulation mode of fatigue crack growth: A case study on cold-rolled SUS430 sheet under cyclic pure shear stress

Abstract

Mechanical modeling for fatigue crack extension mechanisms can be categorized into three types: Plastic Deformation mode of Fatigue Crack Growth (PD-FCG), Damage Accumulation mode of Fatigue Crack Growth (DA-FCG), and Damage Accumulation mode of Fatigue Crack Propagation (DA-FCP). The modeling based on these mechanisms allow for more rational fatigue design than conventional fracture mechanics-based methods without considering the mechanism. However, although some mechanisms have been already proposed, such methods have been proposed only for PD-FCG. This study focuses on DA-FCG, which is influenced by microstructural effects. Fatigue tests were combined with digital image correlation (DIC) analysis to evaluate localized shear plastic strain. A parameter, $\overline{\Delta {\gamma }_{\mathrm{xy},DIC}}$, was introduced as the mechanical driving force for DA-FCG crack growth by averaging $\Delta {\gamma }_{\mathrm{xy}}$ over the plastic zone estimated via continuum mechanics. Furthermore, the Taylor factor M_τ of the shear load—a material index representing resistance to crack growth along shear-driven paths—was introduced. Moreover $\overline{\Delta {\gamma }_{\mathrm{xy},FEM}}$ obtained from EP-FEM and M_τ controlled $\overline{\Delta {\gamma }_{\mathrm{xy},DIC}}$ obtained from DIC were introduced. A correlation between Mτ and $\overline{\Delta {\gamma }_{\mathrm{xy},DIC}}$ was confirmed, indicating their relevance as material properties. Based on these findings, a method for predicting DA-FCG behavior using $\overline{\Delta {\gamma }_{\mathrm{xy},FEM}}$ and M_τ was proposed, offering a framework for microstructure-informed fatigue strength prediction.