Fracture damage evolution of 7075 ultra-high strength aluminum alloy under uniaxial tension with complex loading paths

Abstract

7075 ultra-high strength aluminum alloy is widely applied in aerospace and automotive fields, but its nonlinear complex loading paths during forming intricate damage and fracture mechanisms. A critical gap exists in prior research: the alloy's path-dependent mechanical behavior and damage evolution under multiaxial loading are insufficiently characterized, limiting damage prediction accuracy and forming process optimization. This study addresses this gap by investigating the effects of deformation magnitude and strain rate on the mechanical properties and damage evolution of 7075 aluminum alloy sheets under stamping-tension complex strain paths. The fundamental advancement is the establishment of a high-precision path-dependent damage prediction framework based on the GTN model, which overcomes the limitation that traditional GTN-based applications fail to account for complex strain path effects. To develop this framework, a novel multiaxial loading device was designed for programmable strain paths; response surface experiments combined with finite element inverse calibration were used to optimize GTN parameters, and ABAQUS simulations were validated with experimental data. Results indicate that deformation magnitude dominates damage evolution by enhancing yield strength via cumulative work hardening and delaying damage progression, while strain rate only modulates mechanical strength without altering plastic damage modes. The proposed GTN-based framework effectively captures path-dependent damage progression under complex loading with accuracy over 92%, clarifying the regulatory mechanism of strain path dependence on mechanical degradation and fracture behavior. This work provides a robust theoretical and experimental basis for ultra-high strength alloy damage prediction, enabling precise optimization of practical forming and improved component reliability.