<title>Development of a new crack identification method based on singular current field using differential thermography</title>

Abstract

A new thermographic NDT technique was proposed, in which singularity of the temperature field near crack tips under application of the periodically modulated electric current was measured using differential thermography based on lock-in data processing technique. Experimental investigation was made on the resolution and the applicability in the detection of through-thickness cracks embedded in steel plate samples. Modulated electric current was applied to the cracked sample by an induction coil. Differential thermal images synchronized to the reference current modulation signal were taken by the differential thermography. Significant singular temperature field was observed at the crack tips in the differential thermal images. The cracks were found to be sensitively detected by the proposed technique in good resolution compared with the singular method using a conventional thermographic temperature measurement.