Failure modes of Al-Li alloy friction stir welded stiffened panels subjected to shear load

Abstract

Al-Li alloy friction stir welded stiffened panels have been widely used in many complex structures of aircraft due to their superior advantages. Static and fatigue shear tests were carried out to study the failure modes of 1.2 mm and 1.5 mm thick panels. The static failure modes of panels are weld cracking and skin cracking. The failure loads of 1.2 mm and 1.5 mm panels are 201 kN and 247 kN, respectively. The fatigue failure mode is skin cracking and the cracks initiated from the end of the weld on the panel. The average fatigue life of 1.2 mm and 1.5 mm panels are 47,493 cycles and 45,209 cycles, respectively. The residual stress was measured by the X-ray method and calculated by thermo-mechanical coupling method to study its effect on static and fatigue properties. The maximum longitudinal residual stresses of the left and the right welds are 101.6 MPa and 96.2 MPa, respectively. The fatigue damage evolution model was built to calculate the fatigue life and the crack initiation position of the panels. The result explains the cracks appearing and growing, and it agrees with the experimental finding.