Residual stress caused magnetic field abnormal change upon arc welding joints

Abstract

Residual stress concentration of welding joints is an essential factor to structure safety. It was found that the residual stress could generate a change of magnetic field in arc welding. Things became simple because of the methods based on measuring the distribution of the surface fields and analyzing the relation between the fields and the stress. However, we believe the fact that the magnetizing field caused by electrical current in arc welding has effects can not be ignored. Also, the magnetic field of the Earth is sometimes considered as a critical point in the field's change. In this paper, experiments were carried out to study the role of arc current by comparing the methods of arc welding and laser welding. The magnetic field was measured upon the welding sites. By controlling the input energy, the residual stress was almost the same. The results obtained from these two welding methods varied. Magnetic fields testing from arc welding specimens were changed more sharply than the laser ones. This means that the magnetic change caused by electrical arc current is important to the surface field. Therefore, by analyzing the status of arc current, electro-magnetic methods can be used as non-destructive testing tool of the arc welding joints merely by testing the surface magnetic field without specific magnetization.