Non-Destructive Testing for Detection, Localization and Quantification of Damage on Composite Structures for Composite Repair Applications

Abstract

Composite materials are being widely used for manufacturing aircraft components due to their superior material properties such as high strength, light weight, corrosion resistance, etc. However, compared to isotropic materials, composite materials exhibit complex damage characteristics. Moreover, when the composite material is impacted by a foreign object they are prone to barely visible impact damages such as delamination, matrix cracking, etc. Since composite materials are being increasingly used in aircraft component production the likelihood of composite damage occurrence during aircraft operation increases as well. Therefore, it is crucial to address the challenges associated with detecting composite damage and performing composite repairs. The focus of this research is the development of automated depot repair technology for composite structures, which combines; non-destructive testing (NDT) for damage size determination, damage removal by milling, repair by adhesive bonding of a repair patch and NDT for post repair assessment. In this study, a damaged curved CFRP panel with dimensions of 1.3 × 1.3 m was used for the development of algorithms for automated composite repair process. NDT using a laser line scanner was performed to acquire the composite panel’s surface data, to assess features of the panel such as its shape, visible damage, etc., and the thermographic inspection was done to assess the extent and location of internal damage. Algorithms were developed to perform data fusion of the sensor data; a) to detect, localize, quantify and visualize the damage on the composite panel, through analysis of gradient changes between defined local sections of the panel, b) to generate a 3D model of the repair region based on the surface geometry and with design considerations that ensures the optimal structural integrity of the repaired panel, and c) to output suitable computer-aided design (CAD) files which can be imported to the milling tool, to perform the damage removal, and the CAD tool, to fabricate the repair patch. Finally, after the composite panel undergoes the milling and repair process, NDT inspections will be performed to ensure its safety and integrity.