Double pulsed holography used to investigate noisy brakes

The vibrational characteristics of a noisy passenger car disc brake have been studied using the double pulsed holographic technique which has been developed to allow three orthogonal visual images of a vibrating brake system to be recorded simultaneously. These images show the disc to be vibrating in a bending mode whereas the pad is seen to be excited in a variety of modes such as bending, torsion, and often a combination of both. The development of the technique includes alternative ways of triggering the laser and typical results from the application of these differing methods are also included along with mechanical signals which confirm the visual interpretations. Final results, using a laser trigger delay technique, show that the disc mode waveform rotates about the disc at a rate equivalent to the frequency of vibration divided by the diametral mode order. Early work on a passenger car drum brake is also introduced, this complementing commercial ‘noise fix’ solutions and a proposed theoretical model.