Numerical Simulation And Experimental Studies On Crack Propagation Under The Residual Stress Induced By Laser Shock Processing

Laser shock processing(LSP) is a new surface hardening technology,it has been widely used for the research of material's surface modification.The residual stress induced by LSP can prevent the crack's initiation and propagation very well,thus prolongs material's fatigue life.TC4 titanium alloy and 2024T62 aluminum alloy are the important structural materials in aerospace,so it has important significance to improve the fatigue life of them by LSP.In this paper,the residual stress field in alloy due to LSP was simulated by using finite element modeling on the basis of generation mechanism of LSP induced residual stress,and the modeling results were compared with experimental results.On this basis, the crack propagation under the condition of LSP was simulated with the introduction of the residual stress field by LSP.The main research contents in this paper are listed as follows:The finite element models used for modeling the distribution of residual stresses in alloy due to LSP were created by using ABAQUS software.Some key problems in the model construction were described.The key research focuses on how the parameters of LSP influence the residual stress field.Analysis result shows that there is a threshold value for laser power density.When the laser power density is lower than the threshold value,the maximum magnitude of residual compressive stress on material surface increases at first and then decreases,with increasing the laser power density.When the laser power density is higher than the threshold value,the maximum magnitude of residual compressive stress comes to subsurface and the depth of residual compressive stress increases too.The multiple impacts can obviously increase the magnitude of residual compressive stress at surface and depth of the material.As the impact time increases,the magnitude and depth of residual stress reach saturation value.The present modeling results agree well with the experimental results.On the basis of the research on the residual stress field induced by LSP,the analysis model of crack propagation which takes FRANC2D/L as a platform was created by introducing the residual stress field induced by LSP.The key research focuses on how the residual stress field induced by LSP influences crack propagation. The result shows that the residual stress field has inhibitory effect on the crack propagation and can improve the fatigue life of parts a lot.The crack propagation rate of the sample treated by the LSP decreased significantly.The analysis result agrees with the existed experimental result very well.