NDT of polymer materials using lock-in thermography with water-coupled ultrasonic excitation

Abstract

We present an NDT method that uses lock-in thermography with ultrasonic heating. The acoustical damping causes the mechanical energy to be converted to thermal energy. In the defective regions the damping is stronger resulting in higher temperature generation. Thus the heating is selective to defects and gives good defect detectability. Because defects also affect the heat conduction, the method gives combined information of the change of the mechanical and thermal properties of the sample due to defects. The ultrasonic excitation is amplitude modulated and the magnitude and the phase of the temperature are measured by infrared camera and software lock-in detection. The applicability of the method was proved with several polymer and composite samples having delaminations, impact damages, voids, and inclusions.