The effect of engagement laws on the thermomechanical damage of multidisk clutches and brakes

Frictionally excited thermoelastic instability (TEI) is becoming of major concern in clutches and brakes as larger peripheral speeds and heat loads are required. Using the transient formulation proposed in Afferrante et al. [Wear 254 (2003) 136] and based on a perturbation method, the effect of a fairly general parabolic engagement law is investigated. Two damage parameters Phi(1) and Phi(2) have been introduced related to the maximum surface temperature and the maximum localized frictional heat. Damage maps are presented for the two parameters showing how both initial sliding speed V(0) and acceleration a(0) affect materials durability. It has been emphasized that sliding systems with TEI could work even above the critical speed for a sufficiently long period of time without experiencing severe damage depending on the engagement conditions. Damage maps can be used to define materials and geometry suited to the engagement conditions in order to decrease TEI effects and help in identifying the most critical sets of engagement laws.