Thermoelastic instability in friction clutches and brakes – Transient modal analysis revealing mechanisms of excitation of unstable modes

Abstract

a b s t r a c tSliding systems with frictional heating exhibit thermoelastic instability (TEI) when the sliding speed exceeds the critical value. TEI can lead to hot spots on contact surfaces and is generally of great practical importance in friction brakes and clutches. The phenomenon is well defined in terms of the theory of stability with a classic perturbation approach being commonly used. While the perturbation analysis determines the stability limit, recent interest extends further towards exploration of the unstable behavior. This is motivated by practical reasons, namely by the fact that many common friction brakes and clutches operate instantaneously at speeds exceeding the critical speed for TEI, i.e. in the unstable regime. In order to determine a transient solution, possible mechanisms of excitation of unstable modes of different nature need to be accurately defined and quantified. These mechanisms are normally not considered in stability analysis of the steady-state where an initial perturbation of the thermoelastic field is assumed. In many realistic situations, however, there is no indication of the existence of meaningful initial temperature variation. Lack of full understanding of these mechanisms has perhaps limited broader industrial applications of recent theoretical advances in TEI. In this paper a method of solving the transient thermoelastic process in frictional systems using finite element spatial discretization and modal superposition is presented. Then mechanisms that excite the unstable thermoelastic modes other than the initial perturbation of temperature are studied. The role of the background process (corresponding to nominal applied loads) in the excitation is shown in a clear form and illustrated by practical examples for automotive friction clutches. It is demonstrated, in particular, that while for some geometries and configurations of the sliding system the imperfections determine the excitation of unstable modes, with other configurations strong excitation occurs even in the absence of imperfections.

Numerical analysis of dynamic characteristics of wet friction temperature fields

“…In the process of transmission torque, the steel sheet is more likely to be deformed and destroyed owing to the high temperature and thermal elastic instability. 16 In this article, the temperature difference between the radial and circumferential directions of the dual-steel plate was analyzed.…”

Temperature analysis of a pin-on-disc tribology test using experimental and numerical approaches

“…Zagrodzki [11] studied the frictional heating in sliding systems and the effect of sliding speed on the stability of the system when the sliding speed exceeds the critical value. Finite element model was used to investigate the transient thermoelastic process, and spatial discretization and modal superposition is presented.…”

Mechanical Buckling Induced Thermoelastic Instability in Frictional Clutches

“…For the phenomenon of circumferential distribution friction glazed spots, investigators explained this problem through thermalelastic instability (TEI) theory [10][11][12][13][14][15][16][17][18]. The reasonable explanation is that the friction glazed spots were the result of TEI when the sliding speed exceeded the value of the critical TEI velocity, and while there were pressure disturbances on the friction interfaces.…”

“…From the literature [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24], the energy of higher order thermal buckling or the phenomenon of many "hot spots" is much higher than the real working condition which leads to the circumferential distributed friction glazed spots shown in Fig.1. However, under the action of mechanical load, there exists the possibility of high order buckling, and a buckled disc will subsequently induce TEI.…”