Frictionally Excited Thermoelastic Instability in Automotive Disk Brakes

Thermoelastic instability in automotive disk brake systems is investigated focusing on the effect of a finite disk thickness. A finite layer model with an antisymmetric mode of deformation can estimate the onset of instability observed in actual disk brake systems. Also some effects of system parameters on stability are found to agree well to experimental observations. 1 Introduction Dow and Burton (1972) and Burton et al. (1973) have shown that a small sinusoidal perturbation in the otherwise uniform contact pressure between two sliding half-planes is unstable if the sliding speed exceeds a certain critical value which depends upon the wavelength of the perturbation. This instability, which results from the interaction of frictional heat generation, ther-moelastic distortion and elastic contact, is known as frictionally excited thermoelastic instability or TEI (Barber, 1967 and 1969). It leads generally to the establishment of localized high temperature contact regions known as hot spots. This phenomenon is observed in many practical applications, particularly in brakes and clutches, where significant frictional heating occurs Burton's analysis can be used to obtain an order of magnitude estimate of the speed required to cause TEI, but this estimate is found to be considerably higher than the speeds at which hot spots are observed experimentally in automotive disk brake systems (Kreitlow et al. An important factor in this discrepancy is probably associated with the difference in geometry in that the brake disk has a finite thickness and slides against two pads, one on each side, in contrast to Burton's system of two sliding half-planes with a single interface. In particular, we might anticipate that the finite disk dimension will exert a stabilizing influence on the longer wavelength perturbations, which are those governing the onset of instability. In the present paper, we shall examine this hypothesis by extending Burton's analysis to the case of a layer sliding between two half-planes.