Ultrasonic Evaluation of Young’s Modulus for Reduction of Brake Squeal Noise

Abstract

Elastic properties of friction materials in brake linings are important design parameters because modulus variations may lead to noise generation of braking systems. This paper is to describe about ultrasonic estimation of Young’s modulus of brake linings concerned with squeal noise problem for commercial trucks. Phase velocity of ultrasound propagating through brake lining was measured to calculate Young’s modulus based on elastic relations of acoustic waves with material properties. Two kinds of brake lining samples were produced with the same composition by different manufacturing process, one of which is a traditional product and the other is an advanced one developed for brake noise reduction. Five rectangular samples were cut out from each type of brake linings and machined for ultrasonic test. Acoustic pulse of 500KHz was applied to each sample to calculate the time-of-flight(TOF) for the measurement of wave velocity and Young’s modulus. The results of ultrasonic test indicate that the low noise brake samples have a less deviation of Young’s modulus than the traditional brake samples. This agrees with previous researches and FEM analysis that Young’s modulus variation of brake linings affects the squeal propensity and the instability of brake system.