Shock wave propagation in periodically layered composites

In heterogeneous media, the scattering due to interfaces between dissimilar materials may play an important role in shock wave dissipation and dispersion. In this work the influence of interface scattering effects on shock profile was experimentally studied by impacting flyer plates onto periodically layered polycarbonate/6061 aluminum, polycarbonate/304 stainless steel and polycarbonate/glass composites. Specimens with different heterogeneity were obtained by changing the geometrical configuration (length scale) of the layered stack. VISAR (Velocity Interferometry System for Any Reflector) diagnostic system was used to measure shock particle velocity time history at the rear surface of the specimen. Manganin stress gages were embedded inside the specimen at selected internal interfaces to measure shock stress time history. Two-dimensional numerical simulations were also carried out using the DYNA2D finite element code to understand the process of shock wave evolution in the layered composites. Experimental and numerical studies show that periodically layered composites support steady structured shock waves. The influence of internal interfaces on the shock wave propagation is through the scattering mechanism, i.e., multiple reflection of waves in the layers and their interaction with the shock wave. The interface scattering effect on the bulk behavior of composites is to slow down the velocity of the shock wave, while its influence on the deviatoric response is to structure the shock wave profile. If all the dissipative and dispersive effects are collectively termed as viscosity, which causes the shock front structuring, i.e., increasing the shock front rise-time, then the effective shock viscosity increases with the increase of interface impedance mismatch and decreases with the increase of interface density (interface area per unit volume) and shock loading strength. The existing mixture models for constructing the constitutive relation for composites based on the known properties of its component materials can only, at best, reasonably predict the response of the composites under strong shock loading conditions. In order to fully describe the response of a heterogeneous composite to shock compression loading, accurate physics-based constitutive relations need to be formulated to take into account the scattering effects induced by the heterogeneous microstructure.