Journal of Rheology 

About: Journal of Rheology is an academic journal published by American Institute of Physics. The journal publishes majorly in the area(s): Shear flow & Viscoelasticity. It has an ISSN identifier of 0148-6055. Over the lifetime, 3642 publications have been published receiving 164663 citations.

Analysis of Linear Viscoelasticity of a Crosslinking Polymer at the Gel Point

Abstract: We suggest a very simple memory integral constitutive equation for the stress in crosslinking polymers at their transition from liquid to solid state (gel point). The equation allows for only a single (!) material parameter, the strength S[Pas1/2], and it is able to describe every known viscoelastic phenomenon at the gel point. Measurements were performed on polydimethylsiloxane model networks with balanced stoichiometry for which the crosslinking reaction has been stopped at different degrees of conversion. At the gel point, the loss and storage moduli were found to be congruent and proportional to ω1/2 over a wide range of temperature (−50°C to +180°C) and five decades of frequency ω. The hypothesis is made that this behavior is valid in the entire range 0<ω<∞. This congruence hypothesis is consistent with the Kramers‐Kronig relation and leads to a constitutive equation which shows that, for our polymer, congruent functions G′(ω)=G″(ω) are as much a rheological property at the gel point as are infinite ...

A Theoretical Basis for the Application of Fractional Calculus to Viscoelasticity

Abstract: This article establishes a link between molecular theories that predict the macroscopic behavior of certain viscoelastic media and an empirically developed fractional calculus approach to viscoelasticity. The molecular theory addresses the viscoelastic properties of polymer solids with no crosslinking. It is shown that the results of these molecular theories are equivalent to constitutive relationships written in terms of the fractional calculus. Such relationships, developed previously from an empirical base, have been shown to be useful tools for engineering analyses. The establishment of a theoretical basis for these new constitutive relationships enhances their value, as they may now be used with increased confidence.

The Use of Tensors to Describe and Predict Fiber Orientation in Short Fiber Composites

Abstract: The properties of a set of even‐order tensors, used to describe the probability distribution function of fiber orientation in suspensions and composites containing short rigid fibers, are reviewed These tensors are related to the coefficients of a Fourier series expansion of the probability distribution function If an n‐th‐order tensor property of a composite can be found from a linear average of a transversely isotropic tensor over the distribution function, then predicting that property only requires knowledge of the n‐th‐order orientation tensor Equations of change for the second‐ and fourth‐order tensors are derived; these can be used to predict the orientation of fibers by flow during processing A closure approximation is required in the equations of change A hybrid closure approximation, combining previous linear and quadratic forms, performs best in the equations of change for planar orientation The accuracy of closure approximations is also explored by calculating the mechanical properties o

Flows of Materials with Yield

Abstract: Steady, two‐dimensional flows of Bingham fluids are analyzed by means of a modified constitutive relation that applies everywhere in the flow field, in both yielded and practically unyielded regions. The conservation equations and the constitutive relation are solved simultaneously by Galerkin finite element and Newton iteration. This combination eliminates the necessity for tracking yield surfaces in the flow field. The analysis is applied to a one‐dimensional channel flow, a two‐dimensional boundary layer flow, and a two‐dimensional extrusion flow. The finite element predictions compare well with available analytic solutions for limiting cases.