Real time active thermography for defect detection on arc welding: numerical and experimental analysis for model validation

This work aims to investigate the use of active thermography on welded joints, a non-destructive method which is required if verifications are carried out on working components. Unlike the traditional method, where the workpiece is thermally stimulated by a laser beam at the end of the process, the method here adopted is based on real-time control of welding. By means of a thermal imaging camera, in fact, data collection takes place simultaneously with the welding itself, leading to a considerable reduction in time and consequently in costs. Thanks to Ades Group, at their site in Rovato (BS), four welding tests, monitored by an infrared camera, were carried out to analyze the different behavior of S275JR steel depending on welding method (SMAW and GMAW), material thickness (3mm and 5mm) and type of joint (butt joint and tee joint). All data were analyzed on the ResearchIR software, which enabled us to detect the presence of programmed defects from anomalies in temperature distribution along profiles or weld bead sections. Subsequently, metallographic examinations and hardness tests were carried out to characterize the microstructures and to distinguish the weld bead area, the heat affected zone (HAZ) and the base material. The various data obtained were used on MSC Marc Mentat to create a simulation of the welding process; as an output we can observe thermo-structural characteristics, the evolution of microstructures and deformations. Finally the simulation results will be compared with the experimental ones to verify the accuracy of the model.