A new procedure to evaluate creep data obtained by the helicoid spring specimen technique under conditions of non-viscous creep behaviour

Abstract

A new procedure to obtain true creep rate—stress relation from data provided by the helicoid spring specimen technique considering non-viscous creep behaviour and redistribution of the stress across the coil wire cross-section is presented. Values of coil loads and coil deflections as measured directly in creep experiments are obviously expressed in terms of the initial elastic surface stress and surface strain rate. The creep equation proposed in the present work is transformed numerically into a relation between these integral values and fitted to experimental data. The stress distribution in the steady state is taken into account. It is shown that the true strain rate—stress relation differs markedly from the surface strain rate—initial surface stress relation when the behaviour of the creeping solid is non-viscous, e.g. when the viscous creep and power law (e.g. recovery) creep mechanisms operate in parallel and contribute to creep strain to comparable extents. Also, creep in which coupled viscous and non-viscous deformation mechanisms operate is considered.