Optimization of the excitation and measurement procedures in nondestructive testing using shearography

This paper deals with the development of optimal procedures for nondestructive testing (NDT) inspections using shearography. In the new proposed method a parameter is adopted, the contrast-to-noise ratio (CNR), which allows the quantification of the contrast of the defect to the background in the image. During the calibration of the technique, on samples with known defects, the CNR also takes into account the size and location of the identified defects, compared to those expected. The optimal measurement and loading conditions (e.g., excitation temperature level, time between image acquisitions) are determined by experimental parametric analyses aimed at maximizing the CNR on specimens with known defects. In the present work the developed methodology is described and applied to the definition of best practices for the NDT analysis of aeronautical sandwich composites structures (used in the production of helicopters) by shearography inspection with thermal excitation. In this case the attention is focused on optimizing the thermal loading procedures, but it can be clearly extended to other types of excitation methods.