Theoretical and Experimental Studies on the Thermal Degradation of Wet Friction Materials

A theoretical model for predicting the life cycle of a friction material used in wet friction clutches has been developed and verified. For a given friction material, the degradation mechanism can be identified by performing a Thermal Gravimetric Analysis (TGA) on the samples of worn friction materials. The samples are taken from the friction plates after they undertake various periods of the continuous slip experiments on the full-pack test machine. The degradation rate constants are obtained by performing the TGA experiments on the samples from the continuous slip experiments with different input powers and interface temperatures. The degradation for a dynamic engagement cycle is calculated by integrating the degradation rate with the temperature history near the friction interface as a function of time. The temperature history is predicted by the Borg-Warner computer model for the engagement of a wet clutch [1], which has been verified experimentally. The predicted thermal degradations agree with the experimental measurements on the worn friction samples from the dynamic engagements. This work illustrates that the degradation of wet friction materials in a wet friction clutch can be predicted by a theoretical model using temperature history near the friction interface.