Analysis of Laminated Glass Fractures Caused by .22 Long Rifle at Different Angles

Abstract

This research analyzed fractures on a laminated glass, kinetic energy of the projectile exerted on the laminated glass and characteristics of bullets after hitting the laminated glass when firing from different angles through the simulation of firing a .22 long rifle at the same bullet velocity. Six-mm thick laminated glass coated with 2-mm thick window film was shot from distances between 550 and 650 yards at various angles, including 90, 60, 45, and 30 degrees. The results revealed that at a firing angle of 90 degrees, bullet marks appeared on the laminated glass, forming concentric and radial fractures without penetrating into the glass. At angles of 60, 45, and 30 degrees, the bullets resulted in ricochet marks on the laminated glass, but not in crack. The width to length (W/L) ratio of ricochet mark and bullet hole could be used to calculate the angle of firing. In addition, bullet breakdown after hitting the laminated glass could be used to calculate the firing angle. Microscopic comparison procedure is more accurate than the calculation procedure when it comes to the estimation of the firing angle from the size of the bullet entrance hole and concentric fracture or size of ricochet marks. Contact between the bullet and laminated glass led to kinetic energy change; kinetic energy loss of the bullet can cause the bullet to change its direction and also made fractures on the laminated glass, which would vary according to the firing angle.