Abstract
The steady-state creep rate increases with testing temperature according to the Arrhenius law and its increase with applied stress is usually described by the power law. Simple multiplication of these two laws leads to the dependence of steady-state creep rate on both the variables. Apparent activation energy and stress sensitivity parameter perform in the combined law as constants but most measurements show their dependence on some of the variables. An equation respecting these experimental facts and simultaneously also based on the Arrhenius equation and the power law is derived and verified using some published results of creep tests. It can be presented geometrically by hyperbolic paraboloid. Resulting from this equation, the dependence of yield stress on temperature and strain rate and also an equation describing the relaxation curves are deduced.
Highlights
The steady-state creep rate ε at a given applied stress σ increases with temperature T according to the Arrhenius equation (e.g. Cadek [1])fo \ exp e- Qa o RT where Qa =2 ln fo 2^- 1/RTh v = const. (1)is the apparent activation energy of creep and R is the universal gas constant
Its validity can be verified by experimental results of Vlach et al [7] studying the dependence of yield stress on temperature and strain rate for Cr-Mo steel used for pressure vessels
The temperature dependence can be estimated on the basis of the value of parameter E determined from exponent m of the stress relaxation curves, see Eqs (15), (18) and (19)
Summary
The steady-state creep rate ε at a given applied stress σ increases with temperature T according to the Arrhenius equation (e.g. Cadek [1]). The values of apparent activation energy and of stress sensitivity parameter are implicitly assumed to be constant but most the results of creep tests show that the apparent activation energy depends on applied stress and the stress sensitivity parameter depends on temperature. The solution of these contradictions is the main aim of the present paper. Each of the models leads to certain integer value of stress sensitivity parameter in the range from 1 to 7 (see e.g. Cadek [1]). The approach presented in this paper is fully phenomenological but without any limitation of the stress sensitivity parameter value
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