Creep ductility and modified Monkman-Grant equation for Gr.92 by incorporating total strain

ABSTRACT A modified Monkman-Grant equation, which can provide a more accurate means of predicting creep rupture life than the standard Monkman-Grant formula, has been investigated for Gr.92 using creep data in the NIMS Creep Data Sheets at 550 to 750°C. The t r versus minimum creep rate min plot, which is called the Monkman-Grant relation, deviates downward at low stresses and long times. Better correlation of the t r with the min is obtained by the replacement of t r with (t r /ε r), where ε r is the total or rupture strain. The (t r /ε r) is inversely proportional to the min over a wide range of stress, temperature and test duration, and the magnitude of data scattering is only a little bit even at low stresses and long times. The creep life of Gr.92 can be predicted by evaluating the min, together with the ε r evaluated from the stress and or min dependence.