Nacre: An orthotropic and bimodular elastic material

A new micromechanical model for nacre (mother-of-pearl) is proposed, based on an accurate description of the actual microstructure of the material. In the small-strain regime (where damage and fracture are excluded), it is shown via homogenization techniques that the mechanical behaviour of nacre is: (i) orthotropic, with a strong difference in directional stiffnesses; (ii) bimodular (different Young’s moduli in tension and compression). A simple closed-form analytical solution, and a highly-accurate boundary-elements-based numerical analysis, are developed to evaluate the macroscopic behaviour of nacre from the mechanical properties of its constituents. It is shown that the predictions of our simple analytical model are in excellent agreement with the highly-accurate numerical analysis and with existing experimental data, and it is explained how our model can be further verified through new experiments. Importantly, we show that it is essential to account for nacre’s bimodularity and anisotropy for the correct interpretation of published (and future) experimental data.