Numerical Study of Human Torso Mechanical Response and Injury Assessment Under Blast Loading with Bulletproof Protection

Purpose: With the advancement of weapon technology, explosion injuries have become a major trauma type in modern warfare. Although many studies have investigated blast injuries, most focus on unprotected conditions and lack accurate simulation. This study aims to evaluate the biomechanical response and establish injury thresholds of the human torso under blast loading with and without protection. Methods: THUMS is used to build a coupled human bulletproof air model. Stress distribution and kinematic parameters of key organs are analyzed to assess the protective effect of bulletproof equipment. Results: Bulletproof protection modifies the surface stress of the torso, potentially increasing skin injury risk. For internal organs such as the heart, lungs, and liver, protection maintains similar initial stress patterns but reduces stress propagation and peak values. Its attenuation effect on skeletons is limited and may even increase stress locally. A linear relationship between chest wall velocity and lung stress is identified. The Axelsson injury model is found unsuitable for protected cases, and a model-based velocity threshold corresponding to equivalent peak lung stress is proposed. The stress-equivalent chest wall velocity under protected conditions increased by approximately 14.8% compared with the unprotected case, though this proposed threshold requires further experimental and biological validation. Conclusion: Bulletproof protection significantly alters human biomechanical responses to blast loading. These findings may contribute to refinement of injury assessment criteria under protected conditions and support optimization of both medical treatment and protective equipment design.