Measurement of effective nugget by thermoelastic stress in spot weldments

Spot welding process is completed in very short time and there are many factors affecting on the generation of welding defects. There are difficult to control experimental factors. Even more this is hard to monitor of distribution stress in practical cases. And too much time and expense are required for the experimental trials to find the proper welding condition. The purpose of this study is to investigate the applicability of infrared thermagraphy for the evaluation of weldability in spot weldment. There are some problems in the destructive methods. Furthermore, it is very complicated to apply it on actual structure because of time and cost consuming. Therefore, a nondestructive method for estimating the nugget size has been in continual demand. In this study, thermoelastic stress analysis adopting an infrared thermography for nondestructive evaluation of spot weldability is investigated. Using temperature and stress distribution obtained by infrared camera from adiabatic heat expansion under a repeated load of sinusoidal waves, we estimated the effective nugget of spot welded specimens. To examine the evaluated effective nugget size in spot weldments, they have been compared with the results of microstructure observation from a 5% Nital etching test.