Experimental Investigation of the Time Delay Between a Varying Applied Normal Force and the Resulting Friction Force

Recently, one of the present authors proposed a new model to explain the generation mechanism of brake squeal based on the time delay between a varying applied normal force and the resulting friction force. The present work conducts a series of experimental tests examining the behavior of this time delay using a special test apparatus. The test apparatus suppresses the effect of interference in the time delay owing to the excitation normal force to the greatest extent possible. Several calibration tests of the test apparatus are conducted to ensure the validity of the normal force and friction force measurements. The varying friction force is extracted from the overall friction force signal without phase distortion using a zero-phase filter. The test results demonstrate a time delay between the varying normal force and the resulting friction force under various testing parameters. The time delay is found to increase with increasing excitation frequency. The generation mechanism of the time delay is also discussed.