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This paper presents an application of shearography, an optical method for full-field strain measurement, for evaluating residual stresses in plastic/composite components. The approach is based on measuring the change in slope of the component surface, which is caused by the release of residual stresses, in the vicinity of a small, shallow blind-hole or of a small indentation made on the underside of the component during testing. The severity of slope-change, and hence the fringe density, gives a measure of the residual stresses in the component. This method does not require laborious mounting of strain gages or transducers whose stiffness could affect the accuracy of measurements, and is therefore practical for use in both production and field environment.

A novel computer vision technique for rapid measurement of surface coordinates is presented. The technique is based on the marriage of a digital fringe projection technique and a fringe-phase extraction algorithm. A digitally controlled video signal in the form of linear and parallel fringes of cosinusoidal intensity variation is projected onto an object. The fringe pattern is perturbed by the three-dimensional object surface with fringe-phase containing information on the depth of the object. A phase extraction algorithm is used to determine the fringe-phase distribution, from which the three-dimensional surface coordinates are determined. The theoretical basis of this technique and some experimental results are presented in this paper.