Non-destructive Testing of Planar Defects Using Shearography Method with Modulated Ultrasonic Excitation

Early detection of sub surface defects is very important in the maintenance and development of structures made of composite materials. Therefore , it becomes necessary to use non - destructive tests to improve system reliability and prevent untimely failure of components during operation. However , due to the multi-component nature of the configuration , its complexity , and the extent of various defects in these materials , the detection of defects in composite materials is always difficult .So , there is important to develop some new and advanced methods to detect many of defects in these types of materials . Shearography or laser shearing interferometery , with internal excitation of the defect is one of the novel methods of non - destructive testing of subsurface defects , which detects defects by receiving the defect's surface response to the loading. In this article, a glass fiber-reinforced polymer specimen was subjected to non-destructive inspection using shearography with modulated ultrasonic loading. The parameters influencing the detectability of plane defects were studied , and the obtained results were compared with the usual constant - amplitude ultrasonic loading method . In shearography tests using the amplitude modulation technique , in contrast to the constant amplitude ultrasonic loading , the defect was easily detected at all three excitation frequencies and through the phase and amplitude images . Additionally , the highest resolution of defect detection was achieved at the 43 k Hz excitation frequency . The amplitude image results showed that the defect has higher detect - ability at lower modulation frequencies, regardless of the piezoelectric stimulation frequency . Furthermore , the phase difference changes and defect detect - ability in the phase images are not significantly affected by the piezoelectric excitation frequency , demonstrating the independence of the phase image and the modulating method from the loading conditions .