Thickness effect in laser shock processing for test specimens with a small hole under smaller laser power density

•The stress distribution of small hole samples with different thickness was analyzed.•The relationship between thickness and fatigue life of fastener hole was studied.•The relationship between the thickness and fatigue source location was analyzed.•The difference of fatigue crack growth rate under different thickness was analyzed. In order to consider the influence of the thickness difference of the small hole sample or member on the effect of laser shock processing and the optimization of the process parameters, the differences in residual stress distribution, fatigue source location, fracture characteristics and crack growth rate and their correlations were investigated by simulation and experimental methods after laser shock processing of small hole specimens with different thicknesses under certain power densities. There was a significant difference in fatigue life after laser shock of small hole specimens with different thickness. And there were differences of the fatigue crack initiation and growth mechanism of the laser shocked specimens with different thickness, indicating the small hole specimens after laser shock processing had a thickness effect. This thickness effect was closely related to the distribution of the residual stress due to the difference in plate thickness.