Analysis of temperatures and stresses in wet friction disks involving thermally induced changes of contact pressure

摘要

Thermal distortions of friction disks caused by frictional heating modify pressure distribution on friction surfaces. Pressure distribution, in turn, determines distribution of generated frictional heat. These interdependencies create a complex thermoelastic system that, under some conditions, may become unstable and may lead to severe pressure concentrations with very high local temperature and stress. The phenomenon is responsible for many common thermal failure modes of friction elements and is known as frictionally excited thermoelastic instability (TEI). In the paper, one of the cases of TEI is investigated theoretically and experimentally. The study involves a two-disk structure with one friction disk and one matching steel disk that have one friction interface. An unsteady heat conduction problem and an elastic contact problem are modeled as axisymmetric ones and are solved using the finite element method. The model allows for investigation of thermally induced changes in contact pressure and accompanying temperature and stress fields. The solutions are calculated for real scenarios of clutch engagement recorded in stand tests. In those tests, transient temperatures at mid-radius of the friction surface are measured using a thermocouple. Also time courses of sliding speed, applied force and torque are recorded. Theoretical solutions show specific behavior of the steel disk in the case when sliding occurs on only one side of the disk, leading to high contact pressure in the central part of the friction surface. These predictions are confirmed by experimental tests, which show temperatures at this location higher than the estimated mean temperature of the surface.