Fast Characterization of the Width of Vertical Cracks Using Pulsed Laser Spot Infrared Thermography

Abstract

In-service non-destructive detection of cracks is a challenging task for industries to prevent failures. In the last decades several methods based on infrared thermography have been proposed to detect vertical cracks. In a recent paper, the authors used a lock-in thermography setup with focused laser excitation to characterize the width of infinite vertical cracks accurately. As this method is very time consuming, we propose in this work to measure the width of an infinite vertical crack using pulsed laser spot infrared thermography. A semi-analytical solution for the surface temperature of a sample containing such a crack when the surface is illuminated by a pulsed Gaussian laser spot close to the crack is obtained. Measurements of the surface temperature on samples containing calibrated cracks have been performed using an infrared camera. A least square fit of the surface temperature is used to retrieve the thickness of the crack. Very good agreement between the nominal and retrieved thickness of fissure is found, even for widths down to 1 (Formula presented.) m, confirming the validity of the model.