Computational Insights into High Strain Rate Self-stiffening Mechanism in Nacre

Abstract

It has long been identified that nacre, natural body armor, has extraordinary mechanical properties such as high strength and eminent toughness. What’s more, under dynamic strain rate (~103 s-1), both modulus and strength are surprisingly increased comparing with quasi-static strain rate (~10-3 s-1). However, the mechanism of this unusual high strain rate self-stiffening phenomenon in the ceramic based natural armor remains ambiguous. In this study, a slab model is built to describe stacking fault and twin formation processes when nacre is deformed. Ab initial calculation is carried out using density function theory (DFT) under generalized gradient approximation (GGA). From this model, the surface energy is calculated and compared with experimental data to validate the accuracy of our calculation. The stacking fault energy, twin formation energy along with generalized planar fault energy are calculated to explain the formation tendency of stacking fault and twinning. The findings have uncovered the mechanism of nacre’s self-stiffening properties and provided a new route for designing strong and tough ceramic materials.