Thermoelastic Instabilities in Automotive Disc Brakes — Finite Element Analysis and Experimental Verification

Abstract

The thermomechanical feedback process due to frictional heating in slid-ing systems can cause thermoelastic instability (TEl), leading eventually to localization of load and high temperatures at the sliding interface. TEl in caliper/disc brake systems is an intermittent contact problem, since material points on the disc experience periods of contact with the pad alternating with periods of non-contact. The stability problem is here solved numerically by setting up a frame of reference stationary with respect to the pad and seeking a solution for the heat conduc-tion and thermoelastic equations that varies exponentially in time. The upwind scheme is introduced in the finite element formulation to avoid possible numerical difficulties associated with the large convective terms. A series of brake dynamometer drag tests was made to investigate ex-perimentally the phenomenon of TEl in an automotive disc brake. The temperature field on the rotor surface was measured with infrared (IR) detectors and a high-speed data acquisition system. The Fast Fourier Transform (FFT) method was used to determine the exponential growth rate for various hot spot numbers and critical speeds. Linear extrapo-lation was then used to determine the speed for zero growth rate -i.e. the critical speed. The results for critical speed and the number of hot spots show good agreement with the numerical predictions.