Damage identification in aircraft composite structures: A case study using various non-destructive testing techniques

The application of polymeric composites as materials for structural design of vehicles and other constructions has led to maintain them in safe and effective manner. A special attention should be paid to the aircraft structures, which must be lightweight and reveal superior mechanical properties in order to fulfill growing demands in this industry. Thus, the non-destructive testing techniques applied for such materials should be evaluated in several categories: effectiveness in detection, localization and identification of damage in possible early phase of their development, complexity of application and a cost of inspection. In the following study the authors experimentally tested three composite structures made of glass fiber-reinforced plastic, hybrid composite with a core made of the same material and face sheets made of aluminum alloy and a carbon fiber-reinforced plastic structure extracted from the vertical stabilizer of a military aircraft with barely visible impact damage and delaminations. The tests were performed using various techniques including PZT sensing, ultrasonic, thermography and vibration-based inspection in order to analyze the applicability of these methods in the environmental conditions of inspection of aircraft elements. The performed analysis allows concluding about effectiveness of the applied methods and their specific applications in non-destructive testing of composite elements.