Beyond first-cycle damage: Mechanistic drivers of fatigue crack nucleation in single crystals

作者：Zixu Guo, Xiaochong Lü, Guochen Peng, Daijun Hu, Dawei Huang, Xiaojun Yan, Fionn P.E. Dunne, Huajian Gao, Yong‐Wei Zhang, Wentao Yan, Yilun Xu · 发表于：Journal of the Mechanics and Physics of Solids · 年份：2025 · DOI：10.1016/j.jmps.2025.106393 · 被引用次数：17 · 研究领域：Fatigue and fracture mechanics、High-Velocity Impact and Material Behavior、High Temperature Alloys and Creep

The mechanistic driver for fatigue crack nucleation in metals has remained controversial for decades. To address this, an in-situ digital image correlation technique combined with multi-scale modeling approaches is employed to assess the predictive capabilities of various fatigue indicator parameters (FIPs) for the microcrack nucleation in single crystals. While conventional stress- and strain-based FIPs show limited correlations with observed fatigue cracking sites, energy-based metrics, particularly dissipative energy density (DED) and stored energy density (SED), exhibit significant spatial alignment with nucleation locations. Compared with DED, SED is a more indicative and unambiguous indicator, owing to the incorporation of geometrically necessary dislocations (GNDs). We experimentally reveal a previously unrecognized cyclic-loading effect in low-cycle fatigue: competing strain growth across slip traces generates additional troughs in GND density and corresponding SED peaks, whereas this cyclic-loading effect is absent in high-cycle fatigue. By elucidating the critical role of GND-mediated damage localization, this work advances microstructure-sensitive fatigue damage prediction and provides a physics-based framework for more reliable fatigue life assessment in metallic systems.