Thermally conductive rubber-based composite friction materials for railroad brakes – Thermal conduction characteristics

This study deals with the thermal conductivity of rubber-based composite friction materials used in railroad vehicles. Based on a commercially available railroad friction material, called here base material (BM), various friction materials containing different thermally conductive fillers (Cu, brass, Al, Al2O3 and talc) are fabricated and then their thermal conductivities are measured at various contents of the fillers. Addition of the thermally conductive fillers causes an increase in thermal conductivity of the friction material from 0.48 up to 5.8 W/m K, depending on the type and content of the filler. In addition, the experimental results reveal that the thermal conductivity of the friction material can be influenced by indirect effects including mainly the shape and size of the filler. Fillers with larger size and platelet shape are more effective in enhancing the thermal conductivity of the friction material. In order to provide an engineering tool to estimate the thermal conductivity of the friction materials, a new semi-empirical model is proposed for multiphase systems based on geometric mean model. In this model, the filler may be regarded thermally conductive or non-conductive. The model is first developed for friction material containing multi-non-conductive fillers and one thermally conductive filler and then is extended to a system containing multi-conductive and non-conductive fillers. The agreement between model predictions and experimental measurements is satisfactory.