Mechanism of Fatigue Strength Improvement by Applying Peening Treatment

Fatigue strength improvement method which combined a cleaning treatment with a grinder and a peening treatment is investigated. Although a stress concentration at a weld toe is reduced by the cleaning treatment, the peening treatment does not change the stress concentration. The reduction of stress concentration at the weld toe greatly improves a crack initiation life. The peening treatment can introduce a compressive residual stress at surface layer. Since a residual stress near a crack tip for peened specimens should be compression due to a redistribution of compressive residual stress, a crack propagation rate does not retard only in the compressive residual stress region but in the tensile residual stress region. The compressive residual stress induced by the peening treatment improves the crack propagation life.