Morphological study of fly-ash block under angular impact of 9 mm projectile

Abstract

BACKGROUND: Concrete structures utilized in protective buildings such as ammunition depots and bunkers are susceptible to missile impacts, necessitating a comprehensive ballistic assessment involving penetration and perforation mechanics. Most of the empirical and analytical models for projectile penetration in concrete primarily focus on determining the penetration depth, scabbing, and perforation thicknesses. Concrete structures subjected to firearm attacks exhibit distinct fracture modes that can aid in identifying the firearm used and potential firing locations.
 AIM: This study aims to comprehend the effects of the angular firing of a 9 mm full metal jacketed projectile on aerated concrete blocks, fired from a 5 m range. The goal is to generate hypotheses and conclusions based solely on the observable damage resulting from bullet impacts. A meticulous analysis of the incurred damages can unveil a range of possibilities.
 MATERIALS AND METHODS: The sample comprised 12 aerated concrete blocks, each subject to 919 mm bullets fired from four different angles: 0, 15, 30, and 45. The relationship between impact angle and entry hole dimensions was established using the best-fit ellipse method.
 RESULTS: Examination of the fracture pattern revealed significant damage at both entry and exit holes for a 0 impact angle. As the impact angle increased, the exit hole diameter progressively decreased, culminating in no perforation at a 45 angle. This trend correlated with fracture patterns near entry and exit holes, along with energy dissipation at the impact site corresponding to the impact angle.
 CONCLUSION: A trend was observed between projectile energy loss upon impact and resultant damage to aerated concrete block surfaces. Analysis of aerated concrete block components deposited on the bullets, including rifling details, can help link them to the gunshot openings and firearms recovered at crime scenes.