Nondestructive examination of internal defects in cylindrical glass fiber reinforced plastics using dynamic active microwave thermography

In this paper, the applicability of Dynamic Active Microwave Thermography (DAMT) in nondestructive inspection of GFRP cylindrical shells has been investigated experimentally and numerically. In this regard, Cylindrical GFRP samples were prepared through a filament winding process. Two types of planar and linear defects were created inside the cylindrical samples. Holes and cracks in three different diameters and lengths were engraved on the inner side of the samples. Aiming to create temperature contrast between sound and defected areas a microwave excitation setup comprising a microwave horn antenna, a rotational element, and a Faraday's cage was utilized. Thermal images were captured from the surface of the samples by means of an IR camera. The influences of different parameters including excitation power, heating time, and standoff distance on the temperature contrast were assessed. Besides, in order to examine the electrical field distribution, the interaction of the E-field with the sample, and the temperature distribution on the surface of the sample, the heating process was simulated numerically using the finite element method. The FEM analysis results indicate a proper agreement with the experimental test results.