Relationships between the heterogeneous microstructure, the mechanical properties and the braking behaviour of an organic brake lining material

Abstract

Industrial brake lining materials are composite with complex formulations consisting of multiple constituents. Resulting from the fabrication process, the morphology and distribution of the constituents have significant influences on the future properties and braking performance. In this study, an in-depth analysis ranging from the microscale to the macroscale was performed to assess the relationships between the microstructure, the mechanical properties and the braking performance of an industrial brake lining material formulated for heavy vehicles. It was observed that the manufacturing process had different effects on the morphology and size of constituents and on their distribution in the phenolic binder. The morphologies of large organic particles such as rubber and graphite were affected by the mixing procedure, contrary to those of fibres and mineral particles. A transverse anisotropy consistent with fibre orientation due to cold preforming and hot moulding was observed. The microstructure displayed a strong local heterogeneity right up to the mesoscopic scale at which friction and wear mechanisms typically occur. The mechanical properties were analysed with regard to the heterogeneity of the microstructure to determine the scale at which these properties could be considered to be associated with a homogenised behaviour. The rubbing surface after braking showed that load-bearing localisation depends on the nature, morphology and orientation of constituents but that this heterogeneity can be of interest with regard to the braking ability.