Although linear viscoelastic properties can be measured in many ways, the small-amplitude oscillatory shear test is the most widely used method. Nonlinear viscoelastic properties can also be measured in many ways, but no predominant test method has emerged amongst experimentalists. Whereas there is a unifying theory that describes linear behavior, there is no unifying constitutive theory for nonlinear viscoelasticity. For this reason, each nonlinear test reveals a different aspect of a material’s behavior. Hence, experimentalists have designed various transient experiments to capture different features of nonlinear viscoelasticity.

Large-Amplitude Oscillatory Shear

A novel sliding plate rheometer has been developed that is suitable for use with molten plastics, concentrated polymer solutions, raw elastomers, and other viscoelastic or thixotropic materials. It can generate steady shear rates from 0.05 to 500 s−1 and can also be used to measure linear viscoelastic properties. In addition, it can be used to measure a broad spectrum of nonlinear viscoelastic properties such as the nonlinear relaxation modulus and the shear stress growth coefficient. In order to measure these nonlinear properties it is necessary to generate large, uniform, transient deformations Involving high strain rates. Rotational and capillary melt rheometers are not capable of generating this type of deformation, and until now it was not convenient to use sliding plate rheometers for this type of application. However, the recent development of a reliable and robust shear stress transducer makes it very convenient to use the sliding plate geometry to carry out all of these tests. The new rheometer is described, and examples of the types of data it can generate are shown.

A novel sliding plate rheometer for molten plastics

Although linear viscoelastic properties can be measured in many ways, the small-amplitude oscillatory shear test is the most widely used method. Non-linear viscoelastic properties can also be measured in many ways, but no predominant test method has emerged among experimentalists. Whereas there is a unifying theory that describes linear behaviour, there is no unifying constitutive theory for non-linear viscoelasticity. For this reason, each non-linear test reveals a different aspect of a material’s behaviour. Hence, experimentalists have designed various transient experiments to capture different features of non-linear viscoelasticity.

Using large-amplitude oscillatory shear

https://foodeng.wisc.edu/images/publications/1999-9.pdf

Nonlinear viscoelasticity of cheese

We review notations for, along with ways of presenting, the shear stress responses to large-amplitude oscillatory shear flow (LAOS). We find that the Fourier loss and storage viscosities to be the simplest primal notations for interpreting LAOS. The relative intensities provide the best evidence for oscillatory shear entering the large-amplitude regime. Deviation from linear viscoelastic behaviors can be observed through the distortions of Lissajous loops. We explore these loops in their elastic and viscous projections. The centerpiece of this work is our review table, which summarizes experimental measurements for polymer melts and solutions, targeting 21st century publications. Our review also provides conversion formulae to go from any of many notations to the Fourier loss and storage viscosities. The review table also defines which part of the LAOS measurement field has yet to be ploughed and shines light on which notations have been used, and for which purposes, to interpret nonlinearities.

/pdf/review-of-nonlinear-oscillatory-shear-flow-notations-and-1yfqdkqdw4.pdf

Review of nonlinear oscillatory shear flow notations and presentations: polymeric liquids

A parallel-plate rheometer (PPR) has been constructed for use with the Materials Test System (MTS) for the measurement of fast transient and steady-state responses of polymeric liquids. This particular combination exploits the versatility and capability of the MTS programmable drive system, while the design of the PPR ensures the ideal simple shearing configuration. Instrument compliance, material inertia and mechanical lag in both the input and output components of the system are minimal, thus avoiding defects of most existing rheometers. Reproducible data on a 20% polyisobutylene-in-decalin solution have been obtained for various complicated flow programs. This test system is thus suitable for extensive rheological characterization of complex viscous liquids.

D. W. Mead

Papers

A parallel-plate rheometer for the measurement of steady-state and transient rheological properties