Organic Brake Friction Composite Materials: Impact of Mixing Duration on Microstructure, Properties, Tribological Behavior and Wear Resistance

The lack of knowledge on the link between the manufacturing process and performance constitutes a major issue in brake lining development. The manufacturing process of organic brake friction composite materials includes several steps (mixing, preforming, hot molding and post-curing), which define their final microstructure, properties and performances. This study focuses on the effect of mixing duration on the microstructure, properties and tribological behavior of organic friction composite materials. The adopted methodology is based on simplified formulations effective in limiting synergistic effects by reducing the number and size distribution of constituents. Two simplified materials are here developed according to the mixing duration of the constituent introduction sequence. The microstructural characteristics are studied using 2D and 3D analyses, and then correlated with the thermophysical and mechanical properties. Wear mechanisms and tribological behavior are studied in relation to the microstructure and properties of the materials. The results show the effect of mixing duration as regards particle distribution and fiber arrangement. The distribution and size of fiber entanglements contribute to the formation of carbonaceous particle clusters, which create bulk bridges improving thermal conductivity. Moreover, the arrangement of rock fibers affects density, porosity and thermo-physical properties. In addition, the mixing disrupts the cohesion of fiber bundles with the matrix, affecting compressive modulus and wear behavior. This microstructural defect also fosters abundant third-body source flow, which disturbs the tribological circuit and behavior. Porosities induced by fiber entanglements, having a large and irregular size and distribution on the frictional surface, result in low wear resistance and alter the frictional stability.