Impact fracture of composite sandwich structures

An experimental investigation of impact-initiated failures in high-strength graphite/epoxy and Kevlar-49/epoxy sandwich structures has been conducted. The tests consisted of firing small diameter aluminum projectiles with a velocity range of 16-67 meters/second (52-220 ft/sec) at preloaded sandwich specimens. These tests were intended to be representative of service conditions on materials and structures which might be used as secondary aircraft components. The preload and impact energy necessary to initiate catastrophic failure were determined. The residual strength of impact-damaged specimens was also measured. The results of these tests indicate that catastrophic failures in sandwich structures can be initiated at relatively low preloads by impact projectiles at energy levels well below that required to initiate visible damage.