The effect of creep strain rate on damage accumulation in Type 316H austenitic stainless steel

Many service components in power generation and aerospace industries operate at high temperatures and stresses that make them susceptible to creep deformation and damage. Their complex geometries and load multi-axiality are often treated only approximately in assessing their structural integrity via assessment codes that are based on standard creep tests. For example, the forward creep (defined here as constant load creep) test of round bars is not a true representation of the stress state that service components generally experience. The experiments conducted in this work used notched bar specimens to simulate the effect of stress triaxiality. The results from these experiments were then used to validate a well-established creep ductility exhaustion damage model. Although the damage model is largely based on uniaxial creep rupture tests, it has been previously adapted so that it can be applied to more complex states of stress. Rupture calculations were conducted prior to experimental testing to obtain an estimation of the duration of the experiments. The finite element simulation results, which utilised previously developed creep deformation and damage models, were then compared to the experimental data. It was shown that the model predicted the correct trend for the creep deformation and failure of the specimens and primary, secondary and tertiary creep behaviour of notched bars could be captured. The tests imply that the effective creep ductility was smaller at lower stresses, i.e., at slower strain rates creep strain was more damaging.