A review of residual stress effects on fatigue properties of friction stir welds

Friction stir welding (FSW) is now widely used in industrial manufacturing fields to join metal materials. Although it avoids solidification cracking, the combination of thermal excursion and plastic deformation introduces significant residual stresses. These residual stresses will combine with the applied stresses in service to cause unexpected failure. Therefore, a detailed knowledge of the residual stress effects on fatigue characteristics of FSWs is required. In this review, the experimental, theoretical and numerical studies of residual stress effects on fatigue characteristics of FSWs are summarized, including fatigue crack initiation, fatigue crack growth, stress-life and residual stress relaxation. The applications of residual stress modification techniques for fatigue improvement in FSWs are also presented.