SIGNIFICANCE OF IMAGINARY INITIAL STRAIN-RATE AND STRAIN-RATE ACCELERATION FACTOR IN A CONSTANT-LOAD CREEP

It has been recognized that the logarithm of creep rate varies linearly with true strain in a constant load creep. This empirical law is valid over a wide range of strain and is expressed by a following equation; In epsilon = ln epsilon(0) + S epsilon, where, epsilon(0) is the strain rate, epsilon(0) is the imaginary initial strain rate, S is the strain rate acceleration factor and epsilon is the true strain. This equation has a potential as a powerful tool for creep life and remaining life assessment technology. In the present paper, the physical significance oi the two parameters, i. e., epsilon(0) and S, and their stress and temperature dependences were examined by a simple thought experiment and dislocation models. It was made clear that the imaginary initial creep rate is identical principally with a steady-state creep rate and the stress dependence of S is determined mainly by the work-hardening during creep.