A rotational rheometer for rheological studies with prescribed strain or stress history

A rheometer utilizing an eddy‐current torque transducer and an air‐bearing suspension is described. The rheometer is coupled with a computer‐based data acquisition system and permits studies of shear deformation for several strain or stress histories. A sinusoidal stress history is used to determine the shear storage and loss compliances J′(ω) and J″(ω), respectively. Step stress histories are used to determine the shear creep compliance J(t) and the recoverable complaince R(t) or more complicated linear and nonlinear rheological responses related to these. Deformation at constant strain rate is used to determine the stress growth function or the steady‐state viscosity. The rheometer may be used over the temperature range – 10–180°C, with torque from 1 to 106 dyn cm, and is adaptabel to use with a variety of sample geometrical shapes (e.g., cone and plate, parallel plate, etc.). Examples of measurements on on viscoelastic fluids and on gels below their yield strain are given.