Application of digital shearography in the analyses of surface deformation and photoelastic strain

Abstract

Digital shearography is an optical method for the detection of microscopic deformations and defects in opaque materials. Being sensitive to the spatial derivatives of the displacements induced by stress on the material, shearography allows direct measurement of surface strain, and is not affected by rigid-body motions. Basic principles and setup of a shearography system are reviewed. The technique was applied in the investigation of a canvass under mechanical deformation. Shearograms for increasing deformations and in the presence of sample defects are characterized. The technique is also applied in the investigation of a plexiglass, a transparent material, under sub-surface compaction loading. Initial results suggest that shearography may also be applied to photoelastic strain measurements.