A NOVEL TECHNIQUE FOR PENETRATOR VELOCITY MEASUREMENT IN BALLISTIC PENETRATION STUDIES

A novel experimental configuration that can simultaneously record projectile velocity histories and target back surface out-of-plane motion in penetration experiments has been developed. The technique was used to investigate failure mechanisms during ballistic impact of an S-2 glass fiber woven composite with 60% fiber volume fraction. Microscopy studies performed on recovered samples clearly show interply delamination, fiber breakage, ply inelasticity, and fiber kinking as the major failure modes in these composites. Recorded penetrator velocity histories indicate the failure process is rate dependent. Three well defined regions with different failure zones are observed in the laminate. In a region at the rear of the target plate, Region A, extensive delamination between plies is seen leading to bulge formation. Damage is observed in front of the penetrator with substantial fiber shearing. In a middle region, Region B, tensile fiber failure and large fiber deflection, to accommodate the lateral expansion generated by the steel penetrator, are observed. At the projectile entrance, Region C, fiber microfracture followed by fiber tensile failure is believed to be the failure mode in this region. Noticeable delamination is also produced in plies close to the front specimen surface. Two major fiber failures are observed in the micrographs, fiber kinking and microcracking. Well defined kink bands are seen in Regions B and C on plies with fibers oriented perpendicular to the penetration direction. The formation of kink bands appear to be the result of compressive failure due to lateral motion of the plies away from the advancing steel penetrator.