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Fracture Toughness of Defects Orientated Parallel to a Dissimilar Metal Weld Boundary

Dissimilar Metal Welds (DMWs) are used in many industries to increase the service life of components. Typically a corrosion resistant material is bonded to the internal surface of a second material, this is often referred to as cladding. This type of composite component provides the desired mechanical properties and corrosion resistance without excessive cost. Structural integrity assessments can be used to estimate the remaining life of critical components but these methods are complicated and results are dependent on factors such as: material properties, defect size, defect location and the direction of defect propagation. The cladding process is generally conducted via welding which results in yield strength residual stresses. The interaction between primary and secondary stresses on crack driving force (CDF) are not well understood, particularly at the interface between multiple materials where the microstructure is not homogeneous. These unknown factors contribute to overly conservative structural integrity assessments. This work investigates the fracture toughness of defects orientated parallel the interface of a dissimilar metal clad weld using experimental and finite element (FE) methods. A nuclear grade austenitic clad ferritic steel was investigated. A fracture toughness test was conducted on a CT specimen and the influence of the materials boundary on crack propagation was examined using digital image correlation (DIC). DIC of the fracture toughness test shows that high amounts of strain exist both in the region immediately surrounding the crack tip and in the ferritic material at the material boundary. Post-test analysis of the specimen showed two defects initiated at the root of the notch on the outer surface of the specimen. One longer notch was found internally. Two-dimensional plane stress and plane strain FE analyses were conducted and compared to the experimental results.