Abstract
Key words: Friction, Interface, Contact, Temperature, Measurement, Sliding, Finite Element, Thermal, Brake.
Maintaining appropriate levels of friction interface temperature is important for the overall operating effectiveness of modern friction brakes, and implicitly the safety of the vehicle. This paper considers the distribution of temperature in the friction interface related to real areas of contact. Using Finite Element analysis, thermo-mechanical simulations of a disc / pad brake friction interface have been conducted to predict the temperature at different distributions of real areas of contact across the interface. Factors influencing the magnitude and distribution of interface temperature have been investigated and it has been shown how the relationship between the contact area ratio and the maximum temperature in the friction interface can explain the physical basis for improving the design of brake friction materials by controlling the friction surface temperature. Using a design of experiment approach, factors which are known to affect the friction interface temperature, including the number of braking applications, sliding speed, braking load and type of friction material were investigated in the FE simulations. The results confirmed existing knowledge that the friction surface temperature was most strongly affected by the number of braking applications, i.e. with time of sliding, friction surface temperature reduced and became more evenly distributed across the sliding surface of the friction material. This occurs because the real contact area between the friction material and the rotor changes with time as the interface contact / pressure distribution evolves. However, the results also indicate how the maximum temperature in the friction material surface relates to the contact area ratio; in particular it was found that the maximum temperature in the friction material surface does not increase linearly with decreasing contact area ratio. This offers a route to controlling maximum temperatures in the friction interface by designing the friction material to achieve a specific contact area ratio. The FE predictions have been compared with measurements of friction surface temperature using thermocouple sensors. Very fine thermocouples were inserted into the friction material to measure temperatures in the brake friction interface, and sliding contact thermocouples were positioned to measure rotor temperature immediately adjacent to the friction interface. Using these measurements, the validity of the modelling technique was verified.