Effect of stress state and strain rate on macro–micro damage in Ti-6Al-4V alloy: Experiments and theoretical model

Numerous damage models have been developed to predict material failure. However, existing models often failed to accurately capture the connection between macro damage and micro void evolution across diverse loading conditions. A more robust theoretical framework was therefore needed. In this study, fracture and “strain-freezing” experiments were conducted using a Split Hopkinson Pressure Bar (SHPB) system and specimens of various geometries. Experimental data on micro void evolution under different loads were thereby obtained. Based on these findings, a new theoretical framework describing the process from void nucleation to coalescence was established. A new physical damage model was subsequently developed from this framework. Subsequently, numerical verification was conducted, and this results proved the effectiveness of the new model compared to traditional physical damage model. It exhibited higher predictive accuracy, achieving an average error of 4.29% for fracture strain. This performance surpassed the conventional Gurson–Tvergaard–Needleman (GTN) model (23.98% average error) and the shear-modified GTN (SGTN) model (20.21% average error). Our model was grounded in a more comprehensive physical foundation. The parameters in our model had clear physical meanings, and can be readily determined. It thus offered a robust tool for analyzing the dynamic fracture mechanisms of Ti-6Al-4V alloy. Both experimental and numerical results indicated that stress state significantly influenced the entire void evolution process. This influence altered both the initiation and propagation of macro fractures. In contrast, strain rate primarily affected the velocity of void evolution without changing its fundamental pattern. Consequently, strain rate modified fracture resistance but did not alter the core mechanisms governing the initiation and propagation of macro fractures.