Measurement of Absolute Displacement of a Twin Calliper Disc Brake During Noise

This paper examines the application of the proven technique of holographic interferometry for the measurement and analysis of the absolute displacement, both out-of-plane and in-plane, of a twin caliper disc brake generating noise at 2200 Hz. The standard technique of holographic interferometry has been developed such that both separate dynamic images of the in-plane and out-of-plane vibration, together with a combined dynamic image indicating absolute displacement may be represented. The technique makes use of a series of time related holograms recorded from three different viewing perspectives of the brake. Each image records absolute displacement but as each of the three holograms view the brake from a different viewpoint then each comprises varying degrees of out-of-plane and in-plane vibration, dependant on their angular position. This varying degree of displacement allows their manipulation to identify and isolate the in-plane and out-ofplane contributions to the overall excitation so that each may be considered separately. The out-of-plane is represented as a three-dimensional image whereas arrows represent the in-plane amplitude as a "quiver" plot. The results show the disc modes to be extremely complex for the twin caliper system and further indicate that the in-plane vibration amplitudes are significantly larger in magnitude than out-of-plane vibration amplitudes.