Lightweight design with welded high-frequency mechanical impact (HFMI) treated high-strength steel joints from S700 under constant and variable amplitude loadings

In cases where lightweight designs are particularly in focus, effective fatigue strength improvement techniques like high-frequency mechanical impact (HFMI) treatment can be successfully implemented. Proper HFMI treatment helps overcome the strength limits resulting from local deterioration of the microstructure and local stress concentrators, as well as tensile residual stresses which occur due to the welding process. Investigations carried out under fully-reversed, constant amplitude loading with longitudinal stiffeners of the steel grade S700 show impressive fatigue strength improvement far superior to those observed using other mechanical treatments such as hammering or shot peening. Considerable potential for lightweight design is observed when implementing HFMI; especially in cases which can be characterised by constant amplitude loading. Under fully-reversed, variable amplitude loading with a straight-line spectrum, the fatigue strength could be improved by HFMI. However, the degree of improv