| Abstract: | Step-change stress and strain tests are widely used in fundamental rheological studies of viscoelastic fluids, and their results are important in relation to the potential practical applications of the materials. In this paper, we first give a general review of the experimental and theoretical development of these two tests. Attention is then confined to the creep and recovery (stress) test, which is applied to an implicit rheological fluid model in four different viscometric flows. Numerical solutions, showing the existence of a limiting recoverable strain as a function of stress, are obtained in each of these cases, namely uniaxial extension, simple shear flow, biaxial extension and planar extension. Experimental results of fluid recovery at the relevant high stress levels are not common, but the theoretical results obtained compare favourably with those that are available. Our own experimental results of simple shear flow creep and recovery tests on two polyethylene samples are also used in the comparison. |
