Testing of Adhesive Bonds on Large Industrial Components made of CFRP with a Robot Inspection System Using Active Thermography, Leading to Reduced Cycle Times

The integration of omega stringers to panels made of carbon fiber reinforced plastic (CFRP) by adhesive bonding, which is achieved by baking in an autoclave, must be subject to high quality standards. Failures such as porosity, voids or inclusion must be detected safely to guaranty the functionality of the component. Therefore, an inspection system is required to verify these bonds and detect different kinds of defects. In this contribution, the advantages of a robotic inspection system, which will be achieved through continuous testing, will be introduced. The testing method is the active thermography. The active thermography has major advantages compared with other non-destructive testing methods. Compared to testing with ultrasonic there is no coupling medium necessary, thus testing will be significantly enhanced. To ensure the water to drain away, which is necessary for the function of the ultrasonic transducer, the shell element must be turned upside down in a subsequent step. This is very complex and requires much time. Due to the spatial expansion of the shell elements, a further advantage will be achieved by a continuous movement of the inspection system. In this variant of testing with active thermography, the positioning time for the measurement system is eliminated and by spatial shifting the contrast of failure measurement, a much shorter testing time will be achieved. As a result, the inspection system has the potential to reduce cycle times substantially. Additionally, failures into adhesive bonds can be automatically detected by a down-streamed image processing.