Investigations of in-plane disc vibration using laser holography

Laser holographic methods have been successfully used to produce animations showing the out-of-plane vibrations that take place in both the disc and pad of a real brake system generating noise (squeal). A series of holograms made at different times in the cycle of vibration were used to give the data on which the animations were based. Further it has been shown that mathematical approximations made to the fringe patterns obtained in the holograms by this method give phase and amplitude information about the wave motion involved. It establishes the existence of travelling waves on the brake disc with a speed given by the angular frequency of the noise divided by the mode order.

This approach has now been extended to examine a time- related series of holograms of the disc rim of a brake system. From the data obtained from these holograms it has been possible to develop animations that show the in-plane vibration in the disc of a brake system producing noise. Estimates of the amplitude (of magnitude comparable to that of the out-of-plane motion) and phase of such vibration can also be obtained.