Cost-effective, phase-based thermography method for ultrasonic investigation of defects in CFRP structures

In recent years nondestructive inspection (NDI) methods have found their way into service in the aerospace and automotive industry. Reliable and sensitive NDI systems often represent high acquisition costs for small and medium-sized companies, which represent a significant fraction of aerospace and the majority of automotive suppliers as well as the whole area of high performance sports equipment. For this reason a new approach in thermographic testing is introduced in this work, which combines the advantages of a robust and cheap NDI system such as heat flow thermography with the defect sensitivity of a high performance NDI method such as Lock-In thermography. The data acquisition and excitation is separated, which together with the use of appropriate data management, analyzing software algorithms and cheap off-the-shelf components leads to an effective 2-D NDI system. A carbon fiber reinforced plastic (CFRP) test plate containing various kinds of defects (delaminations, inclusions, fiber cracks, resin accumulations, etc.) is used to compare this thermographic system with the results of a water-coupled ultrasonic system. It is shown that this system has comparable defect sensitivity and even shows advantages in the detection of overlapped defects while simultaneously reducing the total testing time. Furthermore large defect areas can be inspected very quickly.