steadyshear

Steadyshear is a term used in rheology to describe a method and the associated instrumentation that apply a constant shear rate to a material while recording its mechanical response. The goal is to obtain steady-state flow properties, such as viscosity as a function of shear rate, and to study non-Newtonian behavior under controlled deformation.

In a steady-shear experiment, the sample is placed in a geometry such as a cone-and-plate or parallel-plate rheometer. The upper geometry moves at a constant velocity or the instrument controls torque to maintain a fixed shear rate. The device measures shear stress and temperature, from which the apparent viscosity and flow curves are derived. A feedback loop maintains the prescribed shear rate despite changes in viscosity, ensuring a stable state for data collection.

Steadyshear data are widely used to characterize polymers, colloidal suspensions, emulsions, pastes, and foods. They enable the determination of viscosity at different shear rates, yield stress, and whether the material exhibits shear-thinning or shear-thickening. When combined with rest periods, steadyshear tests can also reveal time-dependent phenomena such as thixotropy.

Advantages of steadyshear experiments include reproducible measurements of steady-state properties and straightforward interpretation of flow curves. Limitations include sensitivity to wall slip, sample loading, and temperature fluctuations. Proper geometry choice, surface roughness, and corrections for edge effects help mitigate these issues, ensuring accurate characterization of complex fluids.

See also: rheology, shear rate, viscosity, non-Newtonian fluid, cone-and-plate rheometer, parallel-plate rheometer.