Response of S2-Glass/Vinyl Ester Composites under High Strain Rate Loading - An Experimental and Finite Element Study

摘要

Thick-section S2-Glass/Vinyl Ester composites are used as a structural component in the construction of integral armor. The external ceramic layer of the integral armor acts as a ballistic shield, and the thick composite layer of the interior takes the structural loads as well as it serves as a backing plate for the armor. While the integral armor in its entirety is being treated in another paper, this paper deals with the response of the composite layer alone. Split Hopkinson Pressure Bar (SHPB) has been used extensively to determine the strength of the composite both in the thickness and fiber directions. The strain rate sensitivity of the material has also been determined, and the failure modes are identified. Transient dynamic Finite Element Analysis (FEA) has been performed up to maximum strain rate of 1700 s~(-1). Two different loading conditions similar to experiments are used; one in the thickness direction and the other in the fill direction of the composite specimen. Layered 3D solid elements have been used to model the composite specimens. Transient dynamic analysis has been carried out with incremental time steps, and the stiffness matrix has been considered as a function of displacement and time. Time dependent loading similar to experiments in SHPB is applied as distributed force on the loading surface. Stress propagation and its distribution through the thickness of the laminate are presented. It is observed that FEA can only predict the initial state of deformation of the specimen because the stress computations are based on linear elasticity. It is also revealed from the FEA that during fill direction loading, both interlaminar tensile and shear stresses occur simultaneously at the very initial stage of the loading and cause the specimens to delaminate at a lower stress. The failure modes during the thickness direction loading are however, different. Detailed description of the experimental observations and FEM modeling are presented in this paper.