This paper describes a non-contacting optical method which allows the rapid scanning of large areas to identify regions of high strain. Measurements are made using photographic techniques which allow assessment of strain levels in identifiable 'hot-spots'. The naturally occurring granular appearance of a surface exposed to laser light provides an irregular optical grid for the measurement of surface displacements. The interference pattern produced on illuminating the photograph with a coherent light source was swept by a photosensitive detector driven by a micro-computer. The same computer with suitable disk peripherals acted as a storage and analysis device. A recent advance in the analysis hardware using a vidicon system is described and illustrated.
|Published - 1985