Uniaxial Creep-Rupture Behavior of Low-Alloy Steel Under Variable Loading Conditions

Abstract

One of the analytical tools most used by elevated-temperature designers is the log stress-log minimum creep-rate curve. The curve is normally constructed using at least three and preferably more data points from individual tests. In this paper the possibility of constructing the stress-minimum creep-rate curve using a single specimen programmed for variable step-up and step-down loading is investigated. Both high and low-ductility Cr-Mo- V steels are studied. The results are treated both graphically and analytically to predict rupture under variable loading. Interesting metallographic features of rupture are shown and the results treated using phenomenological theory of anelasticity. It is concluded that a reasonable estimate of the stress-minimum creep-rale curve can be obtained during step-up loading of a single specimen of ductile steel. Among the various techniques for predicting rupture life under variable loading, a strain-fraction method gives good results.