Effect Of Loading Strain Rates On Unloading Behavior Of Shot Peened Materials

Shot peening is a process widely used in industry to improve the fatigue life of materials through induced compressive residual stresses that retard crack initiation and growth. In the peening process, there are two stages: 1) loading: shot penetrating into target; and 2) unloading: shot rebounding from the target. The strain rates in the loading process are known to be in 105-106 1/s range, having heavy impact on the materials’ properties. However, the effect of the loading strain rates on the rebounding stage is not well studied. This paper aims to determine the effects of the loading strain rates on the unloading behavior of a material using FEM method. First, to better understand the material behavior, this study evaluates the loading-unloading responses of one element at high strain rates in different scenarios. Then, it obtains the strain rates during the loading and unloading for the different elements of a material being impinged by one shot. The results show that the unloading behavior of a material depends only on the loading equivalent plastic strain and the strain rate of the unloading step.