A multiscale tribological study of nacre : Evidence of wear nanomechanisms controlled by the frictional dissipated power

Sheet nacre is a hybrid biocomposite with a multiscale structure, including nanograins of CaCO3 (97% wt.% – 40 nm in size) and two organic matrices: (i) the “interlamellar” mainly composed of β-chitin and proteins, and (ii) the “intracrystalline” mainly composed by silk-fibroin-like proteins. This material is currently studied as small prostheses with its tribological behaviour. In this work, the latter is studied by varying the frictional dissipated power from few nW to several hundreds mW, in order to study the various responses of the different nacre’s components, independently. Results reveal various dissipative mechanisms vs. dissipated frictional power: organic thin film lubrication, tablet’s elastoplastic deformations, stick-slip phenomenon and/or multiscale wear processes, including various thermo-mechanical processes (i.e., mineral phase transformation, organics melting and friction-induced nanoshocks process on a large range). All these mechanisms are controlled by the multiscale structure of nacre – and especially by its both matrices and respective orientation vs. the sliding direction.