Investigating the crack driving force of cracks initiating and propagating along the interface of Dissimilar Metal Welds (DMWs)

Dissimilar metal welds (DMWs) are used in many industries to increase the service life of components in corrosive environments. Nuclear power plants (NNPs) use DMWs in numerous locations including critical components such as reactor pressure vessels (RPVs). Structural integrity assessments of these components are complicated due to the changes in microstructure and difficulties in estimating defect location and size. The interaction between primary and secondary stresses on crack driving force (CDF) is not well understood, particular at the interface between materials, leading to structural integrity assessments that are overly conservative. This work considers defects orientated at, and close to, the interface of two materials. The materials investigated are a nuclear grad ferritic steel (A508) and an austenitic stainless steel (308/309L). Experimental fracture toughness testing was conducted using compact tension (CT) specimens. Specimens were notched in three locations: at the interface of the ferritic and austenitic steels, in the HAZ of the ferritic steel and in the HAZ of the austenitic stainless steel. Numerical analyses of each of the experimental studies was also conducted. A thermo-mechanical model of the welding process was used to predict residual stresses prior to testing. Additionally the experimental tests were numerically modelled and the effects on the CDF both including and not including the effects of residual stress are discussed.