Some Aspects of Modelling of the High Temperature Mechanical Behaviour of Nickel Base Superalloys

On the basis of a new physical model based approach a computer package named CRISPEN has been developed jointly by the Cambridge University and the National Physical Laboratory, Teddington. This system allows creep strain prediction engineering alloys subject to various stress and temperature histories using a set of the coupled diff-erential equations . The first describes the strain rate in terms of stress temperature and two internal state variables: an internal stress and a damage parameter. The other two describe the rate of evolution of the internal stress and the damage. A major unresolved problem is the detailed form of the equations describing the evolution of the internal state variables. Different classes of mat- erial may require an altogether different set of equat-ions. However using the simplest possible approach CRISPEN does predict fairly well the creep behaviour of the class of material exhibiting either linear of exponential strain softening such as the superalloys. A detailed analysis of the creep data of a range of superalloys reveals that oiler certain conditions both of these mechanism may occur in parallel