Micromechanical Modelling of Friction Materials

Important constituents contained within modern friction materials include a variety of particles, fibres and fillers (collectively termed “inclusions”) that are added to give desired frictional characteristics to the baseline matrix material. The proposed paper presents the results of a microscopy study which has utilised image enhancement software to measure and evaluate the raw constituents of a typical friction material in terms of size, shape and aspect ratio of inclusions. This characterisation has been extended to determine the statistical distribution of constituent inclusions over the working interface after pad manufacture, as well as to measure the degree of inclusion exposure above the free surface. Experimental tests on the binder system (matrix material plus matrix fillers) have also been undertaken to characterise the thermo-mechanical properties at ambient and elevated temperature. A finite element analysis procedure has been developed to estimate the normal stiffness properties of an embedded particle for different inclusion properties as well as for different levels of exposure above the nominal rubbing surface. This unit cell model has been developed further to determine the transverse load carrying characteristics of the embedded hard particle. Information from the experimental characterisation combined with data from the unit cell model has led to the development of a “multi-component” numerical approach to assess the load bearing and frictional characteristics of the interface.