Fatigue damage mechanism of different single-crystal metallic nanowires in an induced single slip system: An atomistic molecular dynamics study

Metallic nanowires exhibit exceptional mechanical strength and elasticity compared to their bulk counterparts, arising from their high surface-to-volume ratio and limited dislocation activity. However, under cyclic loading, the mechanisms governing their fatigue behavior remain insufficiently understood. Using molecular dynamics simulations, we elucidated the atomistic origins of cyclic deformation and fatigue in aluminum (AlNW) and copper (CuNW) nanowires, characterized by perfect-dislocation slip and deformation twinning plasticity modes, respectively. Under cyclic loading, the AlNW failed after 45 cycles via dislocation slip, which promoted the progressive formation of damaging surface intrusions and extrusions. In contrast, CuNW accommodates a reversible cyclic deformation through twining/detwining process, which stabilizes the crystal structure, suppresses surface instability, and maintains consistent hysteresis behavior over 50 cycles. Quantitative analysis of stress–strain responses, hysteresis energy, and morphology evolution demonstrates a mechanistic correlation between plasticity mode, surface evolution, and fatigue resistance. These findings demonstrate that the dominant deformation pathway dictates fatigue performance at the nanoscale, with twin-mediated mechanisms enabling enhanced cyclic stability. The insights gained here provide fundamental guidance for designing nanostructured metallic systems with improved fatigue durability.