A New Method to “Lock-in” Elastic Effects for Experimental Stress Analysis

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Abstract
A new method is described for “locking-in” an optical interference pattern and a mechanical distortion. The transparent model is cast from a modified epoxy resin with an embedded rubber-thread grid. The model is permitted partially to cure before it is loaded, then held under load while the plastic continues to cure. Upon removal of the load an isochromatic fringe pattern remains which is proportional to the elastic distribution of the maximum shearing stress. In addition, the permanently distorted grid has deformations which are proportional to the elastic distribution of strains. The method is applied to a disk under diametrical compression and a disk under gravitational loading. A comparison of experimental and theoretical results for these two cases shows, in general, good agreement. Most of the discrepancies between experimental and theoretical results are due to the large deformations in the neighborhood of the points of load application. An application of the method to the solution of a three-dimensional problem, namely, the gravitational stress distribution in a buttress-type dam, is discussed briefly.

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