ASTM Recommendations in the Area of Rotational Rheometry

Although the flow in a capillary rheometer is regarded as pressure-driven flow, namely, the shear is generated by the pressure difference along the capillary length, in rotational rheometers the shear is generated between a moving and a fixed surface [9]. 

ASTM D 4440-01, Standard Test Method for Plastics Dynamic Mechanical Properties Melt Rheology  

This test method employs nonresonant forced vibration techniques for determining the complex viscosity (see below) and viscoelastic characteristics of thermoplastic resins as a function of frequency, strain amplitude, temperature, and time. A wide range of frequencies can be used, typically from 0.01 to 100 Hz. 

In these cases the relative velocity of the shearing plates is not constant but varies in a sinusoidal manner so that the shear strain and the rate of shear strain are both cyclic, and the shear stress is also sinusoidal. For non-Newtonian fluids, the stress is out of phase with the rate of strain. In this situation a measured complex viscosity (rf) contains both the shear viscosity, or dynamic viscosity (t] ), related to the ordinary steady-state viscosity that measures the rate of energy dissipation, and an elastic component (the imaginary viscosity ij that measures an elasticity or stored energy)  

These two viscosities are calculated using the following equations  

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