Damage Detection in Carbon Fiber-Reinforced Composite Structures Using Eddy Current Pot-Core Sensor

This work describes the implementation of an eddy current sensor for the non-destructive testing of damage of carbon fiber-reinforced polymer (CFRP) composite materials. The designed sensor has a single pot-core coil, straightforward design, and compact size. In addition, its simplistic structure allows for the development of an analytical model, efficient computer simulations, and rapid identification of optimal testing parameters. CFRP composite specimens with flat bottom holes (FBH) and barely visible impact-induced damage (BVID) were investigated, similarly to the damage observed in the on-life stages of an aircraft exploitation. Inspection results with high sensitivity to detection of damage of both types were presented and compared with the results of the ultrasonic testing. Greater than 3 mm FBH damage, regardless of the hole depths and BVID which was result of 15 J impact energy were successfully detected by proposed pot-core coil. Detailed investigations of the damage attributed to subsurface damage, observable by the eddy current sensor, but not observable for the ultrasonic technique, were evaluated. For the considered BVID about 20% of the change in the resistance value can be attributed to the subsurface defects. This part of the analysis was supported, among others, by computational tomography scans. The results reported in this study confirm that the proposed sensor can be used individually or as a complementary technique for ultrasonic testing in the detection of CFRP composite damage, especially for subsurface damage, which is often not detectable by ultrasonic techniques.