Evaluation of Subsurface Defects in Fiber Glass Composite Plate using Lock-in Technique

In this paper, the lock-in algorithm from lock-in thermography was applied in digital shearography to evaluate the subsurface defects in fiber glass composite plate. Lock-in thermography is one of active infrared thermography which is based on propagation and reflection of thermal wave while lock-in shearography is one of optical interferometric imaging technique which is based on displacement gradient changes in a fringe pattern by mechanical or thermal loading. By applying the lock-in method to digital shearography, its sensitivity can be enhanced by phase sensitive narrow-band filtering as well as the improved signal to noise ratio, selective defects detection. Artificial defects in fiber glass composite plate were evaluated by digital shearography and lock-in shearography NDE techniques to compare their detection capacity. The experimental results confirmed that lock-in method's efficiency on subsurface defects detection in composite plate specimen.