Numerical analysis of optimum treatment parameters by high frequency mechanical impact

In the study, finite element analyses were carried out systematically to investigate the optimum treatment parameters of high frequency mechanical impact (HFMI) on the basis of notch effect reduction and residual stress, which are generally considered to be the dominating factors of fatigue strength improvement of welded joints by HFMI treatment. Taking strain rate into account, the combined isotropic-kinematic hardening model was used to describe the elastic-plastic behavior of the HFMI-treated welded joint of S355 steel. The notch stress concentration factors (SCFs) and residual stresses under different impact depths and diameters of indenter were determined, respectively. Moreover, their synthetic effects on stress distributions of HFMI-treated joints under static load were investigated. It is found that the stress distributions of HFMI-treated joints under static load are affected significantly by impacted groove depth, independent of indenter diameter. The HFMI treatment can achieve the optimal status when the original weld toe is just removed with a groove depth ranging from 0.1 to 0.2 mm. At final, the optimized diameters of 3 to 4 mm are recommended for the indenter in terms of stress concentration and avoidance of crack.