Failure assessment diagrams for cracks in welds with mismatched mechanical properties

The case of a crack located in a weld with a mismatch in mechanical properties from the surrounding base material is addressed. It is shown that both over- and under-matching of yield stress and differences in hardening behavior between the weld and base materials can be treated by defining an equivalent stress-strain curve. This curve depends on geometry, crack size and the mechanical properties of both the weld and base materials. Having defined an equivalent stress-strain curve, a failure assessment curve is constructed using the method of R6 Option 2. Validation for the approach has been addressed by comparison with finite-element results for center-cracked plates, three point bend specimens and cylindrical geometries. A selection of the results for cylindrical geometries is given. An important input to the definition of the equivalent stress-strain curve is the limit load of the mismatched geometry and this is discussed. Conventional assessment methods based on the use of the tensile properties of the weaker material in the weld are also discussed.