Applications of holography and speckle photography to the measurement of displacement and strain

Abstract

Holographic interferometry was used to investigate the behaviour of a plastic pipe joint when subjected to internal pressure. By a combination of ‘live’ and double-exposure techniques the variation of bending moment along an axial surface generator of the joint can be evaluated. To obtain the surface strain, an interferometric technique using speckle photography was used. An important practical factor is the method of mounting the object. For the measurement of much larger surface movements, such as occur when a cantilever is loaded, simple speckle photography, with subsequent point-by-point analysis of the recorded image, is used.