Abstract:
The fatigue crack propagation behavior of laser-MIG hybrid welded joints in 6005A-T6 aluminum alloy is studied. Digital image correlation (DIC) technology is employed to capture the local displacement field near the crack tip during testing, enabling a comparative analysis of crack closure effects between welded joints and base material. The results show that the fatigue crack propagation rates in the laser-MIG hybrid weld specimens are initially comparable to those in the base material specimens but accelerate significantly in later stages. In contrast, the heat-affected zone specimens exhibit notably lower crack propagation rates. A 4% compliance offset value is selected to determine the crack opening force. All specimens follow the general trend of increasing crack closure factor
U with crack propagation. Specifically, the crack closure level in the laser-MIG hybrid weld specimens first decreases and then gradually rises to that in the base material specimens, whereas the crack closure level in the heat-affected zone specimens is initially slightly lower than that in the base material specimens but exceeds that in the base material specimens in later stages without convergence. The Elber equation is applied to correct crack propagation data to eliminate the influence of crack closure on the propagation rate. However, the dispersion of crack propagation data remains largely unchanged before and after correction, indicating that crack closure effects alone cannot fully explain the fatigue crack propagation behavior of joints.