NONLINEAR FINITE-ELEMENT ANALYSIS AND HIGH-TEMPERATURE DEFECT ASSESSMENT

In recent years a methodology has been developed for predicting the complex phenomenon of creep-fatigue crack growth. This is of considerable importance in a wide variety of modern components and structures, for example gas turbines, high temperature pressure vessels and pipework. Essentially the technique involves calculating rates of crack growth for the limiting cases of rapid cycling and steady loading, and then adding the rates to give combined effects. As well as creep data and the well known Paris Law for fatigue crack growth, the method requires linear and non-linear fracture mechanics quantities K and C* to be calculated. K is the well known elastic crack tip stress intensity factor. C* is the creep analogy of the J-integral, defined by: C* = integral (sigma-epsilon-dy - T partial derivative u/partial partial derivative x ds) The paper describes the methodology for determining creep-fatigue crack growth and the application of ABAQUS to determine K and C* for a test specimen and a turbine blade. The use of approximate techniques is also evaluated.