Failure physics analysis of the thermoelastic instability in automotive wet friction disks based on pressure distributions of return springs

Wet friction disks are important components in automotive clutch. Return springs along circumferential direction are widely used to release the friction disks in the disengagement process of clutch. The failures of few springs will lead to non-uniform pressure distributions along circumferential direction, so pressure disturbances are induced. When the clutch engages, the superposition of thermal loads and mechanical loads under pressure disturbances may give rise to some hot spots in contact region. The temperatures of these hot spots grow sharply and the thermal-mechanical feedback processes become unstable. Then thermalelastic instability failure takes place immediately, and the friction disks are damaged. In this paper, typical pressure disturbances in friction disks along the circumferential direction caused by the failures of return springs are obtained by finite element statics calculation. Then the pressure disturbances are expressed as a product of two functions: one is exponential function of time, the other is Fourier function of circumferential temperature. After that, the expressions of pressure disturbances are put into the heat transfer - elastic mechanics coupling equations, and the physics model of thermo elastic instability failure in friction disks is developed by temperature growth rate, disturbances wave number, critical speed, and geometry parameters. The finite element method is used to get the critical speed and temperature field of friction disks when thermo elastic instability failure occurs under pressure disturbances. Finally, the influences of the number and positions of failure return springs on the thermo elastic instability of friction disks are investigated.