LaserShock Peening (LSP) has been successfully used to improve component fatigue performance by bringing beneficial compressive residual stress to material surface since the 1990s. However, it has been found that the compressive residual stress generated by room temperature LSP (RT-LSP) is not stable during cyclic loading. Thus, it is necessary to improve the stability of the compressive residual stress generated by RT-LSP. In this study, Warm Laser Shock Peening (WLSP) is proposed as a potential approach to improve the stability of the compressive residual stress. WLSP is to laser peen a component that is being heated to elevated temperatures. As a thermomechanical treatment (TMT) technique, WLSP integrates the advantages of LSP, dynamic strain aging (DSA) and dynamic precipitation (DP). Through DSA, more uniform and high density dislocations are generated. Through DP, highly dense nanoscale precipitates are generated. Experimentally, WLSP has been evaluated by AISI 4140 steel in terms of the microstructure, residual stress stability and fatigue performance. To investigate the effect of the precipitate particles generated by WLSP to crack propagation, an extended finite element method (XFEM) model was employed. To investigate the effect of temperature to the residual stress distribution, WLSP simulation of copper, a pure metal not applicable to dynamic strain aging, was carried out by finite element model (FEM) and validated by experiments. Through these studies, it has been found that: (1) WLSP can generate high density nanoscale precipitate particles in alloy materials applicable to dynamic strain aging and precipitate hardening; (2) the highly dense precipitate particles generated by WLSP leads to higher material strength than RT-LSP; (3) the pinning force exerted by the precipitate particles to the dislocations leads to higher stability of the compressive residual stress; (4) the highly dense nanoscale precipitate particles generated by WLSP can dissipate the stress concentration near the crack tip and thus decrease the crack propagation speed and improve component fatigue performance.
Purdue University, ProQuest, UMI Dissertations Publishing
Ye, Chang, "Investigation of the Stability of the Compressive Residual Stress Generated by Warm Laser Shock Peening" (2007). Mechanical Engineering Faculty Research. 775.