Mechanical characterization by multiscale instrumented indentation of highly heterogeneous materials for braking applications

This work is focused on the mechanical characterization by multiscale indentation (nano and macro) of a brake pad material, with multiple phases and complex microstructure for applications in the railway industry. Grid nanoindentation tests allowed to identify the mechanical properties of the components in the formulation. The significant difference between constituent’s properties gives a quickly composite response. In parallel, multicyclic macroindentation tests were performed to obtain a composite mechanical response. The properties change according to test locations and configurations of staking phases, due to the high heterogeneity of the brake pad material. The results demonstrated that multiscale indentation tests give a consistent response, which approximates the mechanical properties at different scales. Considering such a very heterogeneous material (broad distribution of properties and particle sizes), the used methodology is appropriate for other heterogeneous complex materials. A multiscale characterization of the mechanical properties is necessary to deal with the problematic of vibrations induced by friction, particularly for brake squeal prediction.