Review and comparison of shearography and active thermography for nondestructive testing and evaluation (NDTE)

摘要

Shearography and active thermography have received considerable industrial acceptance for nondestructive testing & evaluation (NDT&E). They are applicable to all materials: metal, non-metal, composites materials and even biological tissues. The principles and the methods of testing of these two techniques are reviewed, and their advantages and limitations are being compared. Both are optical techniques enjoying the advantages of full-field, non-contact and hence very high inspection speed. 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. Active thermography is a surface thermal radiation measuring technique; it used thermal 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, active thermography needs a controllable thermal radiation excitation to change the surface temperature. Both shearography and active thermography can detect surface and sub-surface flaws, unless the flaw is too remote from the surface. Different excitation methods, such as sonic, induction, flash heating, for the techniques are demonstrated together with some NDT&E applications such as detection of cracks, debonds and other type of flaws.