The design and assessment of modern high temperature plant demands an understanding of the creep and rupture behaviour of materials under multi axial stress states. Examples include thread roots in steam turbine casing bolts, branch connections in nuclear pressure vessels and blade root fixings in gas or steam turbine rotors. At one extreme the simple notch weakening/notch strengthening characterization of the material by circumferentially vee-notched uniaxial rupture tests, as specified in many national standards, may be sufficient. These were originally intended to model thread roots and...