Oblique ballistic impact behavior of composites

An analytical model has been presented for oblique ballistic impact behavior of composites based on wave theory and energy balance between the projectile and the target. The change in obliquity of the projectile during ballistic impact has been studied. The nature of obliquity change depends on the behavior of the target material just after impact and its surface condition. Various energy absorbing mechanisms of the target considered are compression of the target directly below the projectile, compression in the region surrounding the impacted zone, tension in the layers, compression in the lateral direction, shear plugging, friction, matrix cracking and delamination. Analytical predictions are validated with the experimental results. Experimental studies were performed on 4–8 mm thick twill weave fabric E-glass/epoxy composite specimens up to obliquity of 30°. Parametric studies have been carried out on the same target material of 19 mm thickness for the same range of obliquities. Energy absorbed by different mechanisms, change in projectile obliquity, ballistic limit velocity and damage shape and size has been presented. Trends in ballistic limit velocity with the initial projectile obliquity were observed to be different for 4 mm and 19 mm thick specimens.