Challenges for On-Site Automated Ultrasonic Phased Array Inspection of Composite Aircraft

Aircraft maintenance represents 10-20% of the overall operating cost, and heavy C-check and D-check maintenance demands NDT inspection of 100% skin area of composite material fuselages. Delamination and low velocity Barely Visible Impact Damages (BVID) are typical in-service damages found in skin causing small to large sub-surface damages with little or no surface indication. These damages are difficult to detect during manual visual inspection. Conventional manual ultrasonic and advanced Phased Array (PA) scanning of skin followed by data interpretation and analysis for damage sizing is time consuming and cost-inefficient for on-site application; hence a potential task to be automated or robotized. Automated PA inspection by magnetic-adhesion based manipulators, crawlers and scanners have led to rapid inspection rates and lowering the cost of inspection in oil and gas sectors. The composite skin surfaces are painted, smooth and non-magnetic, which invalidates the use of current magnetic adhesion based crawlers for inspection. Despite some previous efforts, the development of automated PA inspection of skin surfaces using a mobile robot is still an unsolved problem. This work is a part of ongoing EU-H2020 project ‘CompInnova’ which aims to develop an integrated NDT approach using combined PA and Infrared Thermography inspection of the fuselage-skin through separate inspection modules mounted on a mobile robot, that will lead to cost-effective combination for on-site automated inspection. A novel vortex based wheeled mobile robot was developed for traversing over the fuselage using adhesion forces generated by means of Electric Ducted Fan (EDF) motors [4]. This robot was designed to carry a PA NDT module [4], but with restrictions on payload (1 Kg.) and minimum water couplant usage requirements. Thus this work presents the development challenges of the PA module for automated PA inspection and to meet the requirements for its integration with robot. PA inspection results obtained by robotic scanning of laminates with impact damages, are evaluated for assessing the functionality and performance of the PA module.