Experimental and Modeling Studies of Stress Wave Propagation in Multilayer Composite Materials: Low Modulus Interlayer Effects

Abstract

The behavior of a multilayer material at high strain rate is investigated by a combination of experimental and numerical techniques. It is shown that, although the Split Hopkinson Pressure Bar (SHPB) at first appears unsuitable for such applications, it is a valuable tool to validate finite element modeling. The feasibility and usefulness of modeling the stress wave propagation in complex multilayer materials was thus demonstrated. The one-dimensional stress state usually assumed for conventional SHPB testing is inapplicable, but it is shown that both numerical and experimental results can nevertheless be coupled for a complete understanding of the wave propagation characteristics. The specific material consists of ceramic face plate and glass/epoxy backing plate with a low modulus interlayer. It is shown that the lateral constraint of an interlayer with a significant positive Poisson’s ratio allows relatively easy transmission of the elastic compressive wave into the backing plate, whereas a low modulus interlayer with an almost zero Poisson’s ratio drastically reduces the ease of elastic wave transmission. The implications for the reduction in damage of the backing layer are discussed. Numerical modeling clearly shows that the severe stress inhomogeneities and discontinuities exist and these may have serious consequences regarding mechanical and other properties. The stress states inside the components are presented here.