FRACTURE-MECHANICS IN THE CREEP RANGE

Cracked high temperature components may fail by crack growth, net-sect ion rupture, or some combination of both processes. This paper reviews the fracture mechanics concepts required to describe this behavior. P rocedures are presented for evaluating relevant characterizing paramet ers using experimental, numerical, and limit analysis methods. Models for predicting crack propagation rates from uni-axial creep data invol ving ductility exhaustion in a process zone at a crack tip are outline d. Both the influence of build-up of damage in the process zone and ma terial deterioration in the uncracked ligament are considered. It is s hown that the models give satisfactory correlations with experimental data.