The role of water in the initial sliding of nacreous tablets: Findings from the torsional fracture of dry and hydrated nacre.

Nacre exhibits remarkable mechanical properties resulting from its hierarchical brick-and-mortar structures. By using pure shear stresses of torsion, we demonstrate how nacre resists the initial tablet sliding by tuning its nanoscale toughening mechanisms in dry and hydrated conditions. In hydrated nacre, hydrogen bonds between water molecules and organic matrices provide temporal paths for stress redistributions, through which the shear resistance is gradually transferred from mineral bridges to contacted nanoasperities. In the subsequent sliding, dynamical interactions between nacreous tablets enable substantial plasticity before the catastrophic failure of hydrated nacre. Our findings should help pursuing further insights into the interfacial behavior of natural and artificial laminated nanomaterials under different conditions.