A Review on Non-Destructive Identification of Defects in Fiber Reinforced Polymeric Base Composites

In recent years, limitations such as the inability to inspect composite materials in common non-destructive testing methods (NDT) have led to the development of new methods such as optical thermography (OPT) and digital shearography (DISH) which are able to resolve these limitations with non-contact and full field inspection. The aim of this paper is to compare the new and traditional NDT methods and also to mention the main features of these new methods such as detection of the defects by stimulating the specimen and receiving its response as out-of-plane displacement derivative (strain) and temperature gradients. The results show that the loading conditions, type of inspected defects, shear amount and the studied material are effective parameters in DISH to accurately estimating the size and depth of defects and also can show that the phase difference between reflected waves for healthy and defective regions in OPT increases up to a specific and optimum frequency value. Moreover, phase difference of waves can be used to determine the defect depth. Additionally, due to the indirect and non-contacting nature of the new methods in measuring defects, the correct determination of the type, size, depth and position of defects is associated with a small percentage of errors. Finally, it is proved that infrared thermography is a quick and effective method for a pass-fail test. Sonic thermography is capable for semi-quantitative evaluation impact related defects and combination of both OPT and DISH methods demonstrated as applicable for full field inspection of composite components instead of traditional methods.