Phase-field modeling for predicting three-dimensional fatigue crack initiation and growth under laser shock peening induced residual stress

Abstract

Laser shock peening (LSP) has emerged as a promising technique for retarding fatigue cracks and improving fatigue performance in metallic structures by introducing residual stress. To numerically investigate fatigue fracture behavior in LSPed metals, herein a three-dimensional (3D) phase-field model incorporating LSP-induced residual stress is utilized, with the model parameters readily determined by experiments. In a typical LSPed titanium alloy TC4, 3D high-cycle fatigue crack initiation (FCI) and growth (FCG) behaviors in fatigue specimens are predicted by phase-field simulation, showing good agreement with experimental results. Predictions for fatigue life fall within the ±2 times error band. Compressive residual stress (CRS) on the surface can reduce the stress level at the crack tip, thus significantly delaying the initiation and growth of fatigue cracks. Fracture surface morphologies during 3D FCI and FCG of as-machined and LSPed TC4 are captured by phase-field simulation, and a triangular crack front morphology caused by LSP-induced residual stress is observed in both experiment and simulation. Impact of residual stress on FCG behavior is systematically investigated to show that high-magnitude CRS on the surface could notably result in prolonging FCG life. This phase-field modeling framework provides an insightful and efficient approach for predicting fatigue performance of LSPed metals.