Friction-induced sheet nacre fracture: effects of nano-shocks on cracks location

Nacre (the pearly internal layer of molluscan shells) is an attractive nanocomposite displaying high mechanical properties, low density and a good biocompatibility with human bones. It is currently studied for both the prosthesis design and the creation of new organic/inorganic hybrid materials by mimicking biomineralisation processes. These exceptional mechanical properties are ascribed to its highly ordered layered 'bricks and mortar' microstructure and more particularly to the energy absorption ability of the mortar during crack propagation. However, this ability appears to be drastically reduced in presence of nano-shocks generated during friction by the dynamic solicitations. This paper compares two Finite Element simulations - a quasi-static compression test and a dynamic impact test - in order to consider the fracture mechanisms induced by friction. It reveals that cracks migrate from the mortar to the bricks, involving in the latter case, the formation of wear nano-debris. These numerical results are confronted with experimental results during friction.