Quantitative analysis on sensitivity of shearography in NDT

Shearography is a very powerful optical technique for both stress analysis and nondestructive testing (NDT) of composite. Sensitivity of the method is somewhat confused. The method has maximum sensitivity as high as holography. The sensitivity is approximately proportional to shear distance when the shear distance is relatively small. How does the sensitivity change from zero to maximum. It is a useful discussion for NDT applications because the size of defects is not very big compared with shear distance. In this paper, the interpretation method for Shearography was studied first. A new method to interpret shearogram, so called 'difference of twin points' displacement', was presented. The method doesn't use the assumption of small shear distance and can be used for sensitivity analysis art any shear distance. A mechanical model of the defect was built to analyze the sensitivity of shearography in NDT. The quantitative relationship between sensitivity of shearography and the shear distance was given after mathematical analysis. Error of classical interpretation was analyzed.