Lightweight potential of welded high-strength steel joints from S700 under constant and variable amplitude loading by high-frequency mechanical impact (HFMI) treatment

Investigations with longitudinal stiffeners of the steel grade S700 under fully-reversed, constant amplitude loading and under variable amplitude loading with a straight-line spectrum show impressive fatigue strength improvement by high-frequency mechanical impact (HFMI) treatment. However, the degree of improvement was for variable amplitude loading lower when compared to constant amplitude loading due to local plasticity which occurs during larger load levels and consequently reduces the beneficial compressive residual stresses. Apart from the HFMI-treatment, the exceedance of constant amplitude loading (Woehler-lines) by variable amplitude loading (Gassner-lines) offers further lightweight potential, despite the lower degree of improvement by HFMI under spectrum loading.