Abstract
An optical, full-field measurement technique called Digital Gradient Sensing (DGS) has been developed for measuring angular deflections of light rays propagating through transparent planar solids subjected to non-uniform stresses. The technique is based on the elasto-optic effect exhibited by transparent materials due to an imposed stress field that cause light rays to deflect. The working principle of the method and the governing equations are presented. DGS relies on 2D Digital Image Correlation (DIC) approach to quantify the angular deflections, which can then be related to spatial gradients of stresses under plane stress conditions. The feasibility of this method to study material failure/damage is demonstrated on transparent planar sheets of PMMA subjected to both quasi-static and dynamic lineload acting on an edge. In the latter case, ultra high-speed digital photography (200,000 frames/sec) is used to perform time-resolved measurements. The quasi-static measurements are successfully compared with those for a line-load acting on a half-space in regions where plane stress conditions prevail. The dynamic measurements, prior to material failure, are also successfully compared with finite element computations.
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