Dynamic Response and Spall Strength of S2 Glass Fiber Reinforced Polymer Composites Liren Tsai and Vikas Prakash Department of Mechanical and Aerospace Engineering Case Western Reserve University, Cleveland, OH 44106-7222 Email: lxt23@case.edu, prakash@mae.case.edu ABSTRACT The utilization of layered heterogeneous material systems in the development of integral armor provides the potential for a dramatic improvement in ballistic performance in a variety of lightweight armor applications. Some of the notable recent examples demonstrating the success of synthetic heterogeneous material systems include composite materials with organic matrices reinforced by glass fibers. In the present study S2-Glass Fiber Reinforced Polymer (GRP) was investigated for its promising potential use as lightweight combat vehicle armor. The GRP composites were made from S-2 glass woven roving in CYCOM TM 4102 polyester resin matrix with resin content of 32% by weight. The objectives of the present study are to investigate (a) the dispersion and attenuation characteristics of the shock waves as a function of shock amplitude and distance of propagation in GRP and (b) the delamination (spall) strength of the GRP both under normal and oblique impact conditions. Plate impact experiments were conducted using 82.5 mm single-stage Gas Gun facility at Case. The shock profiles were measured by using multi-beam VALYN VISAR™ laser interferometer. INTRODUCTION The understanding of materials behavior under dynamic loading conditions is vital to many areas of both civil and military applications. Better understanding of dynamic response has important practical implications connected with impact and blast mitigation, design of lightweight armor, as well as optimal design of other engineered structures with potential threat of shock loading, e.g. composite turbine blades, wings, and fan containment systems. Ballistic threats and multifunctional survivability requirements (e.g., overhead indirect fire fragments, direct fire tank munitions, and increasingly potent infantry weaponry) have encouraged the evolution of ground fighting vehicles to its present 70+ ton status. However, in order to optimize deploy-ability and war-fighting capability in various remote locations, good mobility and ballistic impact resistance ground combat force in any environment is essential for future combat vehicles [1]. This has placed renewed demands on new and improved lightweight and highly damage-tolerant armor materials. The utilization of synthetic heterogeneous materials in the development of armor provides a potential for a major leap in ballistic performance in a variety of lightweight armor applications. Such systems are envisioned to exploit synergistic effects resulting from a combination of dissimilar materials, such as polymers and glasses, thereby developing unique property combinations not possible via other means. The most notable recent examples demonstrating the success of heterogeneous materials include composites with organic matrices reinforced by glass fibers to achieve lightweight and enhanced ballistic resistance [2-4]. The US Army is contemplating to use these materials in the design and development of light-weight integral armor for use in future combat vehicles, platforms and structures. The integral armor has a potential to significantly reduce the combined weight of the armor and the structure compared to the weight of an all-metallic baseline structure with equivalent protection. Even though several alternate designs have been proposed [5-7], common features include ceramic tiles bonded between a thick glass-epoxy structural layer and a thinner cover layer. In this way, transverse impacts by projectiles generate stress waves that propagate through the thickness of the armor. Since the integral armor comprises several layers with very different acoustic properties, predictive analysis of such impacts is difficult; these multilayered structures produce complex patterns of wave reflections, the simulation of which requires proper understanding of the shock and release states and the accumulation of damage within the various constituents. While the shock response of homogeneous materials, such as metals and ceramics has been well documented [8-17], research on shock-induced compression and release in hybrid material systems, such as the GRP, has been very limited [18- 22] and is inadequate to provide guidance in future armor design. This is partly due to the very nature of these composite systems, which is a conglomerate of matrix, fibers, and interfaces between fiber and matrix and between different laminae, various lay-up sequences with different ply orientations and different forms of fiber arrangements within the matrix (particulate,