Experimental and modeling studies of stress wave propagation in multilayer composite materials

The behavior of a multi-layer material at high strain rate was investigated by a combination of experimental and numerical techniques. It was 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 stress wave propagation in complex multi-layer 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.; It was shown that 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 reduction in damage of the backing layer are discussed. Numerical modeling clearly showed that severe stress inhomogeneities and discontinuities exist and these may have serious consequences for the mechanical and other properties. The stress states inside the components were presented. Damage mechanisms were also studied in multi-layer materials. This information was used to validate numerical models developed to aid in the design and optimization of multi-layer materials. The JH-2 and MSC 162 material models were used to simulate the damage evolution and dynamic failure of the ceramic and composite layers respectively. The feasibility of extending the current elastic numerical models for high strain rate loading of complex multi-layer materials into the higher strain and strain rate regimes where significant damage begins to occur was demonstrated.; Plastic deformation effects were also studied in multi-layer materials consisting of ceramic, copper and aluminum subjected to large strains under high strain rate loading. The axial stress distribution was found to be non-uniform in the linear elastic deformation range of the specimen, however, it became uniform in the plastic deformation range even for a single isotropic layer under some circumstances. This non-uniformity level was much more pronounced in the multi-layer materials consisting of different materials.