The Dynamic Strength of a Representative Double Layer Prismatic Core: A Combined Experimental, Numerical, and Analytical Assessment

Abstract

Dynamic out-of-plane compressive testing was used to characterize the dynamic strength of stainless steel prismatic cores with representative double layer topology to be employed in sandwich panels for blast protection. Laboratory-scaled samples of the representative core unit cell were manufactured (relative density of 5.4%) and tested at constant axial impact velocities (ranging from quasi-static to 140 ms−1). The dynamic strength was evaluated by measuring the stresses transmitted to a direct impact Hopkinson bar. Two-dimensional, plane strain, finite element calculations (with a stationary back face) were used to replicate the experimental results upon incorporating imperfections calibrated using the observed dynamic buckling modes. To infer the response of cores when included in a sandwich plate subject to blast loading, the finite element model was modified to an unsupported (free-standing) back face boundary condition. The transmitted stress is found to be modulated by the momentum acquired by the back face mass and, as the mass becomes larger, the core strength approaches that measured and simulated for stationary conditions. This finding justifies the use of a simple dynamic compression test for calibration of the dynamic strength of the core. An analytical model that accounts for the shock effects in a homogenized core and embodies a simple dual-level dynamic strength is presented and shown to capture the experimental observations and simulated results with acceptable fidelity. This model provides the basis for a constitutive model that can be used to understand the response of sandwich plates subject to impulsive loads.