Shock Wave Propagation in Functionally Graded Mineralized Tissue

In this investigation, the shock wave propagation in bone-like tissue was investigated. The Alligator gar (Atractosteus spatula) exoskeleton is comprised of many disparate scales that provide a biological analog for potential design of flexible protective material systems. The gar scale is identified as having a two-phase architecture, (1) bioapatite mineral and (2) collagen protein, forming a biological composite with two distinct layers where a stiff, ceramic-like ganoine overlay a soft, highly ductile ganoid bone. The ganoine layer anchors into the bone layer using a “sawtooth” type structural feature. The structural feature, porosity, and elastic modulus were determined from scanning electron microscopy, 3D micro-tomography, and dynamic nanoindentation experiments towards developing an idealized computational model for finite element simulations. The computational analysis employed a brittle damage model to determine the influence of the structured interface has on the stress response. The elastic modulus was functionally graded through the thickness of the fish scale. The sawtooth geometrical interface, and the moduli gradation were explicitly modeled through a representative volume element to allow for an in-depth stress analysis. The results from a plate impact simulation using the commercial ABAQUS finite element code showed that structured interface induced additional shear wave reflection thereby significantly increasing local damage accumulation.