Review of interaction of bullets and fragments with skin-bone-muscle parenchyma

Abstract Penetrating projectile injuries from bullets and fragments remain a leading cause of casualties in modern warfare. Understanding the mechanical interaction of these projectiles with biological tissues is crucial for designing and optimizing both modern ammunition and protective systems. Towards this end, we review the mechanics of the interaction of the projectiles with various biological tissues. The review focuses on the relationship between projectile characteristics (velocity, shape, design), specific tissue, and the resulting injury. The aim is to understand the relationship between these factors and the energy or energy density required to inflict specific tissue-specific injuries. The review highlights the distinct failure mechanisms for each tissue for bullets and fragments. Skin failure is manifested by a combination of crushing, shearing, and elastic hole enlargement. Bone fracture predominantly shows conical cavity formation and associated radial and concentric cracks. Muscle and brain failures involve shearing and temporary cavity formation. Eye, due to its delicate nature, is highly susceptible to penetration by small projectiles with minimal compression. The data suggests significant variations in the energy density needed for perforation depending on the tissue type and projectile characteristics. For example, skin perforation requires a lower energy density (0.1-0.2 J/mm2) compared to bone (0.05-3.2 J/mm2). Further, the traditional 80 J energy criteria of a projectile for defining the lethality threshold might be overly conservative, especially for smaller projectiles. This review also highlights the importance of considering energy density as casualty criteria.