Comparison between the sinh and effective stress equations for secondary creep rates

Abstract

Many mathematical expression have been proposed for describing the creep behaviour of metals at elevated temperatures. One well-established expression is in sinh equation ϵ s = c ∗ { sinh(αδ)} n ∗ while more recently an effective stress equation ϵ s A ∗′ (σ−σ 0) p has been developed. The effective stress equation has been shown to have a sound physical basis and to have implications for creep behaviour in general. The sinh expression, however, is empirical and restricted essentially to the secondary creep stage but it is possibly more convenient to use for stress analysis and creep damage summation situations. However, in view of its empirical basis the question arises of whether in fact it provides a meaningful description of creep behaviour. To answer this an evaluation of the sinh equation was made by comparing it directly with the effective stress approach. This revealed some inconsistencies and a modification to the sinh equation is suggested which, it is believed, results in a more realistic equation.