Review and Comparison of Shearography and Thermography for Nondestructive Testing

Shearography and thermography have received considerable industrial acceptance for nondestructive testing. This paper will review the principles and the methods of testing of these two techniques, and compare their advantages and limitations. Both are optical techniques enjoying the advantages of full-field, non-contact and hence very high inspection speed. They are applicable to all materials: metal, non-metal, composites materials and even biological tissues. A fundamental difference between them is the mechanism of detecting flaws. Shearography is an interference optical technique which measures surface deformation and reveals flaws by looking for flaw-induced deformation anomalies. Thermography is a surface thermal radiation measuring technique; it used the radiation properties to measure the distribution of surface temperature of the object. It detects flaws by the flaw's anomalous heat transfer response. The methods of testing are also different. While shearography requires application of stresses to produce deformation, thermography needs a controllable thermal radiation to change the surface temperature. Both shearography and thermography can detect surface and sub-surface flaws, unless the flaw is too remote from the surface. Some applications of the techniques to the detection of cracks, debonds and other type of flaws will be demonstrated.

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