Predicting Tensile Behavior and Fatigue Life of Laser Shock Peened Titanium Alloy by Crystal Plasticity Model

Abstract

Laser shock peening (LSP) could improve fatigue resistance of metals, but the complex surface microstructures created by LSP make it extremely challenging to predict the mechanical behavior. Here, we present a crystal-plasticity (CP) modeling framework to predict the tensile behavior and fatigue life of LSPed titanium alloy, in which LSP induced three strengthening mechanisms (i.e., residual stress, grain-size gradient, and dislocation) are fully involved. The fatigue life is evaluated by incorporating CP finite-element results and a modified Tanaka–Mura model. The three strengthening mechanisms of LSP and their individual contribution to the tensile and fatigue properties are quantitatively clarified. The predicted tensile behavior and fatigue life of LSPed titanium alloys are demonstrated to agree well with experimental results. In terms of tensile property, the major strengthening contribution is ascribed to the LSP induced grain-size gradient, followed by dislocation and residual stress. As for fatigue life, most predictions are within the ±2 times error band. It is found that balancing residual stress with grain size and dislocation is crucial for improving fatigue life. This work provides a predictive approach for evaluating tensile and fatigue performance of LSPed alloys, and is insightful for fatigue life enhancement by LSPed microstructure engineering.

Keywords: crystal plasticity, laser shock peening, fatigue life, Crack initiation, titanium alloy