Relationships for tensile creep under transient stresses

Abstract

The tensile creep occurring during and immediately after loading has been studied for an 11 per cent chromium steel and a nickel-base alloy at elevated temperatures. It was found that the strains incurred during loading are dependent upon loading rate and can be estimated from consideration of the equations for static creep by using the assumption of strain hardening. The strain incurred during slow loading causes the processes of creep to be at a more advanced stage when the static phase commences so that the resulting strain rates are also dependent upon the rate of loading. Rapid loading tends to produce almost wholly elastic strains so that the subsequent static phase involves a more fundamental shape of creep curve. The approach was extended to consider minimum creep rate and fracture, and it was shown that they could be related to applied stress by use of the creep equation. The shapes of the stress-strain hysteresis loops were also derived from the creep equation and estimates based on static-creep data were shown to correlate with experimental data from repeated-tension cycling with a triangular wave shape.