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The moiré method in thermal fields

Differential moiré method is used to analyze the strains and stresses in externally loaded bodies at elevated temperatures

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Abstract

The differential moiré method was used for the analysis of strains and stresses in externally loaded bodies at elevated temperatures. A technique was developed to reproduce a crossed grating of a density of 500 lines/in. on the surface of the specimens in both principal directions. This grating resisted temperatures up to the glowing point of the material tested. An arrangement of cameras allowed full-scale copying of the crossed model grating on the ground glass of a camera. Mechanical-interference patterns in both directions were obtained by superimposing various linear reference gratings on the image of the model grating. The moiré fringes produced in both principal directions of the specimen with reference gratings of slightly different pitch were photographed by a second camera. These fringes yielded the displacement distribution of the specimen with great accuracy.

The main advantages of the method are the following: the thermal conditions of the specimen remain undisturbed from any contact with an aline body as, for example, a glass reference grating. The method can be applied at any temperature provided the specimen does not glow at this temperature. It is versatile, sensitive and accurate. It can be applied directly to any material under testing and, therefore, it is independent of the scaling factors between materials of models and structures, and it can be used for steady-state temperature fields as well as for transient-temperature strain fields.

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Authors and Affiliations

  1. Pennsylvania State University, University Park, Pa

    Pericles S. Theocaris (pressently Vistiting Professor of Engineering Mechanics)

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  1. Pericles S. Theocaris
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Theocaris, P.S. The moiré method in thermal fields. Experimental Mechanics 4, 223–231 (1964). https://doi.org/10.1007/BF02322955

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