Surface strain measurement of rotating objects using shearography instrumentation based on fibre-optic imaging bundles

Quantitative, full-field surface strain measurement is achievable using shearography instrumentation that employs at least three measurement channels. The system presented here possesses four measurement channels consisting of four views of the object. Images from the four views are ported to the shearing interferometer using fibre-optic imaging bundles. The use of fibre-optic imaging bundles simplifies the experimental arrangement considerably, allowing full-field surface strain measurements to be made using just one CCD camera and one shearing interferometer. Simultaneous capture of data from the four measurement channels using a pulsed laser source allows the measurement of surface strain on dynamic objects. In this paper the use of the instrument to make measurements of the surface strain profile of a PTFE plate rotating at 600 rpm is described. The use of the spatial carrier technique allows the deformation induced phase variation to be calculated across the field of view from just two images recorded from the object on subsequent rotations.