Experimental investigation on normal and oblique ballistic impact behavior of fiber metal laminates

In this work, the normal (0 degrees) and oblique (30 degrees and 45 degrees) ballistic impact behavior of glass fiber-reinforced aluminum laminates (fiber metal laminate, FMLs) impacted by a rigid cylindrical projectile (with a flat nose) has been investigated from an experimental point of view. The ballistic impact tests were conducted on the FMLs using a one-stage gas gun at different impact angels, i.e. 0 degrees, 30 degrees and 45 degrees. A high-speed camera was used to capture and record the experimental images and data during the impacting process. Different failure patterns were observed in the FMLs under oblique and normal impact, with the differences concentrated on the initial crack (in the back surface) and plugging damage (in both the front and back surface). The angular change in direction of the projectile during perforation was only observed during oblique impact tests while the maximum value of the angular change was observed when the impact velocity was close to its ballistic limit velocity. In addition, the angular change decreases with increasing impact velocity and is almost constant when the value of vi/v50 reaches a critical value. It can also be observed from the impact test results (both normal and oblique impacts) that FMLs exhibited the lowest ballistic limit velocity when the impact angle was close to 30 degrees. In particular, normal impact shows a higher ballistic limit velocity than that of oblique impact while the ballistic limit velocity at impact angle 45 degrees is slightly higher than that at 30 degrees.