Numerical and experimental description of the welding residual stress field in tubular joints for fatigue assessment

Abstract

In order to achieve fatigue resistant welded structures, it is necessary to manage and control welding process-related factors which affect the fatigue strength. These factors are sometimes present as welding defects and sometimes as inevitable residual stresses which are unwanted by-products of welding processes. This subject has been treated in welding research communities since the 1950s. However, the extent of this effect was unclear and is still a matter of debate. Having advanced predictive tools for accurate determining welding residual stresses will not only lead to the possibility of considering precise welding residual stress effects during life estimation but also can be useful to have effective measures for the subsequent mitigation or modification of the welding residual stress fields. The objective of this study is to describe experimentally and numerically the welding residual stress field in welded tubular joints made of structural steel S355J2H in terms of two different case studies. Residual stresses in cylindrical specimens with dummy welds (case-1) and bead on tube welds (case-2) are determined experimentally by means of x-ray, synchrotron, and neutron diffraction techniques. The SYSWELD software is used to calculate the welding residual stresses numerically by integrating the metallurgical transformation effects in order to compute the link between material microstructure and residual stresses. Thermal and metallurgical calculations couple the temperature field and phase proportions by considering the latent heat of fusion/solidification and the transformations in the transient heat conduction equation. Obtained results which include both thermal and metallurgical history are used as input data for mechanical calculations afterward. The accuracy of the both thermal and structural models is validated through experiments for temperature distribution and residual stresses.