Multiple laser shock peening effects on residual stress distribution and fatigue crack growth behaviour of 316L stainless steel

Laser shock peening (LSP) is one of the life enhancement processes by inducing compressive residual stresses into the material. The effects of repeating LSP pattern on the residual stress is investigated numerically in this study. A 3-D finite element model was developed to obtain residual stress field in the material. FEM results have shown that increasing the number of peening impacts increase the magnitude and depth of compressive residual stress. Also the average surface residual stress in the impact region increased from -291 after 1 impact to -326, -343 and -356 MPa after 2, 3 and 4 impacts respectively. Moreover, the effects of repeating LSP pattern on fatigue crack growth properties were investigated experimentally by performing tests on C(T) specimens made of 316L stainless steel. The test results have shown that the fatigue crack growth life is very sensitive to the number of peening impacts and increased from 84,380 cycles in untreated sample to 104,130 cycles in sample with 1 time LSP and 170,500 cycles to sample with 2 times LSP. Also the fatigue crack growth rates decreased by repeating LSP patterns on the test specimens.