Numerical study on damage identification using shearography with different shearing amounts

Abstract

Shearography is a technique appropriate for the analysis of damage, namely by allowing the direct measurement of the gradient or derivative of the displacement field, i.e. the rotation field. This technique is based on the subtraction of the phase of laser light coming from the reflection at two neighboring points in the surface. The distance between these two points define what is called shearing amount. The measurement sensitivity can be adjusted by varying the shearing amount, such that we obtain large sensitivities with high values of this parameter. However, high values of shearing amount lead to the smoothing of the results. In this paper, a study on damage identification in beams using shearography with different shearing amounts is reported. Damage indicators based on differences in modal curvatures are applied to data coming from simulation of shearography. These damage indicators show a great dependency on the shearing amount, such that, for instance, with large values of this parameter the damage is spread across a larger area than the actual one. The peak values of the damage indicators present an attenuation and the damaged area also increases with the shearing amount. According to the findings presented in this paper, it is advisable to take precautions when localizing damage with measurements obtained with shearography.