Analysis of creep-dominated tensile stress-strain data

• New method for extracting creep characteristics from tensile stress-strain curves. • Validated via example calculations based on published sets of curves. • Applicable when creep is relatively rapid and curves are not affected by necking. A novel analysis is presented of tensile nominal stress-strain data, covering a range of strain rates, for cases in which the behaviour is dominated by creep. Example calculations are carried out using reported outcomes from several publications: no new experimental data are presented. An important part of the analysis is conversion of the raw nominal data to true values, for stress, strain and strain rate. Two procedures are described for extraction of creep characteristics from experimental data of this type. The first is based on a simple logarithmic plot, with a combination of a true stress and a corresponding true creep strain rate being obtained from each test having a given nominal strain rate. The other involves the use of a simple numerical model, which can be implemented using a spreadsheet, with creep parameter values being obtained via optimisation of the fit between experimental and modelled stress-strain curves. These approaches offer attractions for obtaining creep parameters via experimental procedures that are simpler, more robust and easier to carry out than those of conventional creep testing. They are, however, applicable only to cases for which the rates of creep are relatively high and there is no early necking. Behaviour during tensile testing of samples undergoing rapid creep successfully modelled, allowing creep characteristics to be extracted from a set of conventional stress-strain curves