Strain Rate Dependent FEM of Laser Shock Induced Residual Stress

Abstract

Laser Shock Peening (LSP) is a process by which the energy of a laser burst produces a plasma shock, transmitting mechanical forces into a substrate material. On metallic structures, LSP produces residual stresses in the substrate which can extend fatigue life and improve surface hardness (Eisensmith, Fatigue effects of laser shock peening minimally detectable partial-through thickness surface cracks. MS thesis, Air Force Institute of Technology, 2017). These resulting stresses are difficult to predict, however, as the LSP process is difficult to model. This difficulty stems from the relatively unknown temporospatial profile of the pressure impulse in relation to settings in the LSP process. A better correlation is desired between FEM predictions, and empirical residual stresses. Residual stress profiles on LSP treated workpieces have been determined by Neutron diffraction in prior work (Eisensmith, Fatigue effects of laser shock peening minimally detectable partial-through thickness surface cracks. MS thesis, Air Force Institute of Technology, 2017). Simulations using Johnson-Cook equations and Mie-Grüneisen equation of state (EOS) were run in Abaqus using an assumed pressure impulse. Initial results show qualitative agreement with empirical LSP results, but still have room for model optimization.