Application of X-ray diffraction to determine the residual stresses in a sub-merged arc welded joint in the 2-MN-test facility
Source: BAM, division Weld Mechanics
Welded components, such as those found in nuclear power plants or offshore installations, are often subject to high safety requirements. A mechanical failure or the occurrence of cracks must be avoided. To be able to evaluate the mechanical stresses present in such components, very complex and expensive tests must be carried out, because of the size and complexity of the parts. The determination and evaluation of so-called residual stresses, as a measure of the inherent mechanical load, is often the focus of attention. But how can the boundary conditions present during the production of welded components be transferred to the laboratory? A simple downscaling to the usual laboratory scale is often not possible, since very different heat conduction (welding) and shrinkage restraint (mechanical stiffness) are present. Welding mock-ups are therefore increasingly applied to simulate the stiffness present in the real component on a manageable test piece. Also, for the numerical simulation of the stresses present in the real component, such mock-ups are used as benchmarks. Nevertheless, the lack of knowledge of the exact stiffness condition is often disadvantageous. The concept of the restraint intensity is an approach to quantify the stiffness present in real components, which can be transferred then to the laboratory scale. A 2-MN test system developed at BAM offers the possibility to apply these restraint intensities on welded specimens. In addition, the forces and moments occurring during welding can be monitored online. Preheating and subsequent heat treatments can be evaluated as part of the production process that way. The local residual stresses can be determined, for example, with X-ray diffraction on the restrained specimens. The article provides an overview of tests already performed and their results. The presented test concept allows the transfer of the boundary conditions of the real component to the laboratory scale and vice versa. The determined stresses then correspond in their magnitude to the residual stresses effective in the real component. Their effect on the component behavior can thus be simulated and evaluated.
From the field to the lab: Real scale assessment of stresses in welded components
Arne Kromm, Thomas Lausch, Dirk Schröpfer, Jonny Dixneit, Andreas Hannemann, Thomas Kannengießer
published in Materials Performance & Characterization, Vol. 7, Issue 4, pages 574-593, 2018
BAM, division Weld Mechanics