Effects of biaxial residual stress components on mixed-mode fatigue crack propagation behavior in friction stir welded 7075-T6 aluminium alloy panel

Residual stress in friction stir weld (FSW) joint significantly affects fatigue performance. It can often combine critically with the applied load cause premature fatigue failure. Research on the residual stress effects on fatigue behavior is required to assess the damage tolerance issues in FSW joints. In this study, the effect of biaxial residual stress components (longitudinal residual stress and transverse residual stress) on mixed-mode crack propagation behavior in FSWed 7075-T6 fuselage panel was studied. Residual stress profiles across the welded plate were measured by X-ray diffraction technique. Fatigue crack propagation for mode mixity angles of 30 degrees, 45 degrees and 60 degrees were carried out. The stress intensity factors (SIFs) at the crack tip were evaluated by finite element method and used to study the effect of biaxial residual stress and the individual component on mixed-mode crack behaviors. The results show that the variation of crack path is strongly linked with the residual stress component as well as the initial oblique crack angle. SIF components are affected by the individual residual stress component. Both two components are required to study the mixed-mode crack propagation in FSWs.