Interaction of Residual Stresses With Applied Stresses in a Dissimilar Metal Electron Beam Welded Specimen

Dissimilar metal welds are often used in nuclear reactors to connect the ferritic components to the austenitic stainless steel pipes. One of the pressing concerns of such design is the presence of cracks at the interface. The situation is further complicated by the differences in the yield strength at the interface compared to the base materials, the existence of residual stresses in high magnitude and the loading conditions of the crack in service. Residual stresses when combined with the service loads may affect the susceptibility to failure. Therefore studying the interaction between the applied and residual stresses in a component is crucial to understand the fracture behaviour and the accurate failure assessment of cracks. The objective of the following research is to assess the fracture behaviour of the crack located at the interface of a dissimilar metal weld between the ferritic P91 steel to an austenitic AISI 316LN steel made from electron beam (EB) welding, using a 3D elastic-plastic finite element analysis under the presence of residual stresses. A numerical model was developed to simulate the fracture behaviour of cracked body under applied load in the presence of residual stresses from the welding process and predict the J-integral around the crack tip. The numerical model was developed in stages to simulate the welding process, extraction of C(T) blank specimen and finally the behaviour of the cracked body under residual stresses and service loads. The model was validated at various stages using neutron diffraction measurements on the welded plate, after the C(T) specimen extraction but prior to the introduction of the crack and the residual stresses around the crack tip after the introduction of crack.