The influence of work hardening and residual stresses on the fatigue behavior of high frequency mechanical impact treated surface layers

In the present study, the effect of process-induced residual stress and work hardening was separately analyzed to describe the fatigue life improvement by High Frequency Mechanical Impact (HFMI) treatment. For this purpose, blunt notched specimens made of mild steel S355J2+N and high strength steel S960QL were HFMI-treated under different mechanical pre-stress conditions. In that way, the effect of residual stress and work hardening could be separated. The generated residual stress states were measured by means of X-ray- and neutron-diffraction techniques. Based on the FE post processing the fatigue life was estimated using a damage mechanics evaluation with the consideration of the HFMI-induced residual stresses.