Comparison of Stroboscopic Shearography and Time-Average Shearography Methods for Nondestructive Testing

Shearography is a powerful optics method, which is capable of measuring derivatives of displacement, surface strains, and nondestructive testing. Time-average shearography and stroboscopic shearography have been developed for full-field vibration analysis. In this paper, the capability of time-average shearography and stroboscopic shearography for nondestructive testing has been compared using a proposed shearography configuration. In order to generate vibration, the proposed experimental system was equipped with a piezoelectric excitation mechanism. The time-average and stroboscopic shearography inspections were carried out by sweeping the excitation frequency of the piezoelectric. Stroboscopic shearography successfully detected the defect in the frequency ranges of 1300-1600, 6000-8000 Hz and 12600-13300 Hz, while time-average shearography detected the defect only in the frequency ranges of 6000-8000 Hz, and 12900-13100 Hz. The results of inspections of propylene specimen with a 10 mm circular hole indicated that stroboscopic shearography provides a more reliable assessment than time-average shearography. Compared to time-average shearography, stroboscopic shearography gives more clear fringes in the all frequency range. In addition, stroboscopic shearography could recognize the defect in wider frequency ranges.