Transient analysis of frictionally excited thermoelastic instability in multi-disk clutches and brakes

A 2D multilayered model has been considered to estimate the transient evolution of temperature and pressure perturbations in multi-disk clutches and brakes during operation. The model proposed by Decuzzi et al. has been modified here to estimate the variation of b–perturbation growth rate—with V—relative sliding speed. It has been verified that the perturbation with the lowest critical speed has also the highest growth rate, and that low frequency perturbations are less critical than high frequency perturbations, at fixed critical speed. Therefore, when comparing perturbations with identical critical speed, those with higher wave numbers are responsible for more intense thermomechanical damages. Also, for perturbations with wave number smaller than the critical mcr, the temperature increases with m; vice versa for perturbations with wave number larger than mcr the temperature decreases with m. A reduction in thickness ratio a1/a2 between friction and metal disks has the effect of increasing the temperature and growth rate. An approximate formula for the temperature variation with time has been derived for a linearly decreasing engagement speed.