Image processing for the laser spot thermography of composite materials

This paper describes an image processing algorithm in support of infrared based nondestructive testing. The algorithm aims at analyzing the raw thermal infrared images obtained by using the nondestructive evaluation method of the laser spot thermography. In the study presented in this paper, a laser was used to scan a test specimen through the generation of single pulses. The temperature distribution produced by this thermoelastic source was measured by an infrared camera and processed with a two-stage algorithm. In the first stage few statistical parameters were used to flag the presence of damage. In the second stage the images that revealed the presence of damage were processed computing the first and second spatial derivative. Two spatial filters were also used to enhance contrast, and to locate and size the defect. The algorithm was experimentally validated by scanning the surface of a CFRP and a GFRP composite plate with induced defects.