Multiscale Simulation of Crack Propagation in Impact-Welded Al₄Cu₉ Alloy Based on Cohesive Zone Model

Al₄Cu₉ welding alloys are critical in aerospace cable applications, but their fracture resistance with micro-defects remains insufficiently studied. This work develops a multiscale crack propagation model integrating molecular dynamics (MD) and finite element (FE) methods under the cohesive zone framework to investigate fracture mechanisms. At the microscale, embedded atom method (EAM)-based MD simulations with pre-existing defects (non-defect, blunt crack, and blunt crack + void) reveal dynamic crack propagation behaviors, quantitatively extracting bilinear traction-separation constitutive parameters. Macroscale FE modeling links these parameters to macroscopic fracture toughness, demonstrating that composite defects (blunt crack + void) reduce fracture energy by 39.95% and stress intensity factor by 31.31%, exceeding single defects' impacts (31.27% and 12.02% reductions, respectively). Temperature effects (200 K to 500 K) further reduce fracture energy by 22.50% and stress intensity factor by 25.68%, though defect-induced fracture toughness fluctuations (relative standard deviation = 18.40%) dominate over temperature effects (10.00%). These results validate the multiscale approach in bridging micro-damage evolution to macroscopic fracture behavior, offering critical insights for reliability design and lifespan prediction of Al-Cu alloy welding cables in aerospace engineering.