Comparison of two creep crack growth parameters, C* and Q*, with FE analysis

This paper presents a numerical study of creep crack growth in a compact tension specimen using elastic-plastic-creep Finite Element (FE) modelling. The constitutive behaviour of a carbon-manganese steel at 320°C, 360°C and 400°C was described by a power law creep model. A damage-based approach is used to predict the crack propagation rate using a node-debonding technique. Analyses at a fixed load at different temperatures and different loads at a fixed temperature were performed to predict crack extension under plane stress and plane strain conditions. Three parameters, K, C* and Q* parameters, are used and compared to characterise creep crack growth (CCG) rate. Comparisons were made with available experimental CCG. When the K parameter is used there is both load and temperature dependence of CCG rate. When the C* and Q* parameters are employed for the characterisation of CCG rate, initial tails are observed in the early stages of crack growth for all FE predictions. The FE results indicate that under full steady state CCG rate versus C* or Q* there is little dependence on temperature and load under plane stress conditions. Whereas under plane strain conditions there is dependence observed with temperatures and load for both the C* and Q* parameters.