Influence of interfacial geometry on the energy absorption capacity and load sharing mechanisms of nacreous composite shells

The excellent mechanical properties of nacreous composites are partly attributed to its staggered microstructure, which is made of multiple layers of mineral tablets bonded through a soft protein matrix. An important parameter that could affect the load sharing mechanism in nacre is the waviness of aragonite tablets. In this work, a continuum model of nacre composite is developed, which takes into account the waviness factor. The tablets are subjected to tensile loading and are initially modeled to have dovetail shapes with varying slopes. The load sharing efficiency of nacre is evaluated through displacements, stresses and strain energy density (SED) of the unit cell. The SEDs of unit cells, tablet and matrix are presented for different overlapping lengths and inclination angles, from which maximum SEDs and optimum overlapping lengths are determined. Parametric studies show that larger inclinations of nacre tablets result in higher energy absorbing capacity. A more general case is also presented, where nacre's platelet is modeled to have sinusoidal waviness of different wavelengths. By varying the wavelength while maintaining the periodicity of the unit cell, stresses, SEDs and displacements are obtained and compared. Analytical results on the optimum waviness of designed unit cells are validated with observed nacreous microstructures.