Absolute displacement measurements of a brake disc during self generated noise

The measurement of in-plane vibration of a noisy disc brake is both difficult to
measure and difficult to verify. In the past there has been a reluctance by researchers to accept
the contribution of a displacement parallel to the surface of the object, or in-plane
displacement, to noise generation. In addition to measuring absolute displacement it has been
difficult to isolate the in-plane and out-of-plane components of displacement using either non-
contact or conventional displacement measurement techniques. However within the last few
years techniques have been developed to allow absolute displacement to be measured. Such
systems are now commercially available but validation of these systems remains vague. In
parallel with these commercial systems the technique of classical holographic interferometry
has been extended to allow examination of both out-of-plane and in-plane displacement of a
brake disc during noise. This paper outlines the development and the validation of this system
on a disc brake system generating noise.