Deformation mechanisms in nacre

Nacre (mother-of-pearl) from mollusc shells is a biologically formed lamell ar ceramic. The inelastic deformation of this material has been experimenta lly examined, with a focus on understanding the underlying mechanisms. Slip along the lamellae tablet interface has been ascertained by testing in com pression with the boundaries oriented at 45 degrees to the loading axis. Th e steady-state shear resistance tau (ss) has been determined and inelastic strain shown to be as high as 8%. The inelastic deformation was realized by massive interlamellae shearing. Testing in tension parallel to the tablets indicates inelastic strain of about 1%, occurring at a steady-state stress , sigma (ss) approximate to 110 MPa. The strain was associated with the for mation of multiple dilatation bands at the intertablet boundaries accompani ed by interlamellae sliding. Nano-asperities on the aragonite tablets and t heir interposing topology provide the resistance to interfacial sliding and establish the level of the stress needed to attain the inelastic strain. D etailed mechanisms and their significance for the design of robust ceramics are discussed.