عنوان مقاله [English]
Digital shearography, as a non-destructive testing method is based on laser interferometry, which detects defects by measuring the mechanical response of the specimen to the external loading. In this study, thermal loading was applied in an alternating way to the conventional shearography method in order to investigate its effect on the defects ascertainability in different sizes and depths. A total of 15 lock-in shearography tests with different modulation frequency and loading cycle were carried out on a polymer specimen with 9 planar defects in different sizes and depths and the results were compared with conventional shearography. In the conventional method, only 4 out of 9 defect areas were detected in the specimen, while by applying lock-in stimulation with a modulation frequency of 0.02 Hz, all of 9 defect areas were revealed. The results showed that increasing the number of loading cycles does not have a significant effect on the detection capacity of defects. Also, detection of deeper defects requires the implementation of lower modulation frequencies, and defects detectability is improved with decreasing modulation frequency, so that the mean phase difference increases 2.1 times by reducing the modulation frequency from 0.1 to 0.02 Hz.