Elastic Properties of Nacre Aragonite Tablets

Nacre has recently attracted the attention of the research community. This biocomposite has exceptional strength and toughness with respect the materials it is made of. The design of nano and micro composite inspired from nacre requires a deep understanding of nacre microstructure and mechanical properties. In this work, the elastic properties of aragonite tablets in nacre were determined using nanoindentation on cleaved specimens from a Red Abalone seashell. Aragonite has a significant elastic anisotropy, and has a strong texture in nacre tablets. Low penetration depths (<50 nm) were employed to avoid the effect of the interfaces. The results were strongly disturbed by the surface roughness of the specimens. Standard analysis methods failed to give consistent results. Instead, a Hertzian contact analytical solution was fitted onto the experimental curves when roughness effects were accounted for. The results demonstrate that the presence of intracrystalline proteins in the tablets do not significantly deviate their elastic properties from those based on single crystal aragonite elasticity. The methodology presented here can be used for other similar cases such as thin films on substrate.