Fast sizing of the width of infinite vertical cracks using constant velocity Flying-Spot thermography

Abstract

Constant Velocity Flying-Spot thermography consists in scanning the sample surface by a focused CW-laser spot moving at constant speed. This technique was designed to study large surfaces in short times. In this work, we propose a method, based on a Flying-Spot thermography setup, to size the width of vertical cracks by fitting the temperature profile along the line that contains the center of the laser spot and is perpendicular to the crack to its analytical expression. This method is also valid in the opposite configuration, where the laser spot remains at rest and the sample is moving at constant velocity. This configuration is useful for in-line inspection in factories, for detecting and sizing cracks in real time, without stopping the production chain. Experimental measurements on stainless steel samples containing calibrated vertical cracks confirm the validity of the method to measure the crack width with high accuracy, even for submicronic wide cracks.