Rheology Of Fiber Suspensions Research Articles

Rheology of fiber suspensions using MRI

The suspensions of non-Brownian fibers are of interest for many applications. Although many studies concerning suspensions are available in the literature, most of them concern suspensions of spherical particles. In this paper, global and local rheology of fiber suspensions are explored near the jamming transition. A critical volume fraction is extracted from the experimental data. The value of this critical volume fraction is in agreement with the expected value of the concentration of rigid rods above which the isotropic phase becomes unstable. Moreover, non-reversible effects of the shearing are observed in flow curves because of the non-Brownian behavior of the studied fibers.

The use of principal spatial tensor to predict anisotropic fiber orientation in concentrated fiber suspensions

The Phelps-Tucker anisotropic rotary diffusion (ARD) equation constitutes an important development in relation to concentrated fiber suspension rheology and is significant in its ability to predict transient, flow-induced fiber orientation, especially for long fiber composites in the industry. Within this model, a critical spatial tensor was assumed to be a polynomial tensor-valued function depending on both the orientation tensor and the rate-of-strain tensor. However, it can be difficult to derive a large number of fitting ARD parameters. For simplification, we newly defined the spatial tensor as coaxial with the orientation tensor's principal directions, while the spatial tensor's principal components are to control anisotropic changes in the orientation tensor. Such a principal spatial tensor used in the Phelps-Tucker ARD model is demonstrated in accurately predicting the shell-core structure of fiber orientation distributions for injection molding simulation of long fiber composites, supported with e...

Numerical predictions of fiber orientation and mechanical properties for injection‐molded long‐carbon‐fiber thermoplastic composites

The use of long carbon fiber‐reinforced thermoplastic composites as lightweight automotive materials offers superior mechanical performance compared to glass fibers. However, the anisotropic fiber orientation distribution with shell–core structure is critical to determine mechanical properties. Recently, both theoretical models of fiber orientation—Anisotropic Rotary Diffusion and Reduced Strain Closure and Improved Anisotropic Rotary Diffusion and Retarding Principal Rate—have been significantly developed in the field of fiber suspension rheology. From injection molding simulations, numerical predictions of fiber orientation are derived with related experimental validations, while dramatic changes in orientation distribution are discussed at various fiber concentrations and different polymer matrices. More importantly, the reinforcing ability is discussed in regard to the tensile modulus and the stress–strain response for a variety of long carbon fiber composites. POLYM. COMPOS., 39:3726–3739, 2018. © 2017 Society of Plastics Engineers

Numerical prediction of fiber orientation and mechanical performance for short/long glass and carbon fiber-reinforced composites

Fiber reinforced polymer (FRP) composites offer exciting new possibilities for the green automotive industry, owing to their excellent mechanical properties, advantageous weight reduction and economical fuel consumption. In practice, accurately predicting fiber orientation is a critical issue in causing anisotropy in the mechanical properties of the FRP parts. Recently, an objective fiber orientation model, iARD-RPR (Improved Anisotropic Rotary Diffusion model combined with a Retarding Principal Rate model) proved significant in the field of fiber suspension rheology. Using state-of-the-art injection molding simulations, we therefore used the iARD-RPR model to explore the fiber orientation changes for various fiber components in regard to fiber length (short and long fibers) and fiber type (glass and carbon fibers). Under an extreme condition of higher fiber concentration and longer fiber lengths, a thicker core region and a narrow shell are always found in a typical orientation pattern of injection molded FRT parts. More importantly, these predicted orientation distributions provided to micromechanical material modeling computation of mechanical properties aid in the discussion on the reinforcing ability of short/long fibers and glass/carbon fibers based on the numerical simulation results. Comparisons with experimental data are also presented herein.

Obtaining repeatable initial fiber orientation for the transient rheology of fiber suspensions in simple shear flow

Many researchers reporting the transient rheology of fiber suspensions have not experimentally verified the initial fiber orientation. An assumption for the initial orientation is then required to simulate the fiber orientation evolution and stress response. Measurements of fiber orientation obtained prior to testing in a rheometer can confirm the homogeneity of fiber orientation throughout a sample and repeatability between multiple samples. In this work, the transient rheology of glass fiber suspensions above 0.5 mm in length was measured in a sliding plate rheometer with the initial fiber orientation generated through compression molding, flow reversal, and injection molding. Measurements of shear stress and fiber orientation were obtained to evaluate each sample preparation method and to gain insight into the stress-microstructure relationship. Preshearing and applying flow reversal was used in an effort to control the initial fiber orientation for transient shear stress measurements, but fiber orient...

Prediction of fiber orientation distribution in injection molded parts using Moldex3D simulation

In the automotive industry, glass‐filled thermoplastics are used in air intake manifolds, radiator tanks, and many other parts. However, widespread application of glass‐filled thermoplastic materials has been limited in many cases by the inability to accurately predict performance and durability. Since a more accurate fiber orientation prediction will lead to more accurate local mechanical property predictions, this work investigated a recently proposed mathematic model of fiber suspension rheology, which considers the anisotropic fiber diffusion and fiber–matrix interaction from a microscopic viewpoint. The new model proved able to predict many details of the fiber orientation distribution and could be applied advantageously as part of the product and manufacturing development processes. POLYM. COMPOS., 35:671–680, 2014. © 2013 Society of Plastics Engineers

One and two-fiber orientation kinetic theories of fiber suspensions

The morphology influencing rheological properties of suspensions of rigid spheres constitutes the flow induced collective ordering of the spheres characterized by two or more sphere distribution functions. When the rigid spheres are replaced by rigid fibers, the collective order in the position of the spheres is replaced by the flow induced orientation of the fibers that suffices to be characterized by one-fiber orientation distribution function. A flow induced collective ordering of fibers (both in position and orientation), that can only be characterized by two or more fiber distribution functions, can still however constitute an important part of the morphology. We show that two types of interaction among fibers, one being the Onsager-type topological interaction entering the free energy and the other the hydrodynamics interaction entering the dissipative part of the time evolution, give indeed rise to a collective order in the orientation influencing the rheology of fiber suspensions.

Rheology of fiber suspensions in viscoelastic media: Experiments and model predictions

The rheological behavior of suspensions of short glass fibers in different fluids has been studied. Transient tests on presheared samples of fiber suspensions in Boger fluids showed that orientation of fibers not only depends on the strain, but also on the rate-of-strain. The experimental results show that upon increasing fiber concentration and/or fiber aspect ratio, the steady shear material functions of fiber suspensions increase at low shear rates, whereas at high shear rates, these material functions approach those of the matrix and become almost independent of fiber characteristics. A rheological model based on the modified Jeffery equation for the fiber motion and a Hookean energy model, formulated within the GENERIC framework, for the matrix has been developed to quantitatively predict experimental data for suspensions of fibers in different fluids. A quantitative comparison of experimental data with model predictions shows the ability of the model to predict the rheological behavior of fiber suspensions in viscoelastic media.

Experimental Study of the Rheology of Fibre Suspensions

Experimental Study of the Rheology of Fibre Suspensions

The rheology of fibre suspensions

We review theoretical work on the rheology of fibre suspensions. We seek to clarify one or two confusions in published work and also give a small improvement to Batchelor’s formula for extensional viscosity of suspensions of long fibres between the dilute and semi-dilute régimes.

Rheological characterization of commercial glass mat thermoplastics (GMTs) by squeeze flow testing

AbstractThe flow behavior of commercial glass mat thermoplastics (GMTs) has been investigated by isothermal axisymmetric squeeze flow testing between parallel circular plates. Tests have been performed over a range of squeeze rates and the analysis is based on simple power law constitutive equations. A key part of the work is determining the relative contributions of shear and extensional flow to the overall squeezing force response. By developing a variational flow model, based on the upper bound theory, the behavior has been found to be predominantly extensional, with shear effects becoming important at very small plate separations. In addition, a predictive model for the radial pressure distribution during squeezing has been developed, based on fiber suspension rheology. Since fibers are generally long or continuous, treating the material as a statistically homogeneous fluid does not yield accurate results in this respect.

Dynamic simulation of microstructure and rheology of fiber suspensions

AbstractA numerical simulation method has been developed to predict the motion of fiber suspensions in various flows by using the particle simulation method (PSM), in which a fiber is modeled by an array of spheres. The hydrodynamic interaction among fibers is considered by decomposing into intra‐fiber and inter‐fiber interactions. For the intra‐fiber case, the many‐body problem is solved by calculating the mobility matrix for each fiber to obtain the hydrodynamic force and torque exerted on each sphere. For the inter‐fiber case, only the near‐field lubrication force is considered between spheres belonging to different fibers. The methodology was applied to predicting the microstructure and rheological properties of rigid fiber suspensions in simple shear flow and fiber orientation in two‐dimensional diverging flow by combining this method with the finite element method (FEM). In the former, the overshoot of suspension viscosity, due to the transient change of the microstructure, was observed in semi‐dilute to concentrated systems. In the latter, the calculated fiber orientations agreed with expectations of theory.

Analysis of Rheology of Fiber Suspensions by the Particle Simulation Method

Analysis of Rheology of Fiber Suspensions by the Particle Simulation Method

On the effect of nonhomogeneous flow fields on the orientation distribution and rheology of fiber suspensions

AbstractThe influence of nonhomogeneous flow fields on the orientation distribution and rheology of fiber suspensions is investigated. The Stokes‐Burger model is used to approximate the forces and moments on the fiber for the subsequent calculation of fiber angular velocities for nonhomogeneous cases where the velocity gradients vary over the fiber length. For simple shear flows, an analytical solution based on the Stokes‐Burgers model is derived. Fiber angular velocities are compared to previously published results. An iterative numerical technique is developed to calculate the otherwise indeterminate fiber angular velocities for other nonhomogeneous flows, such as non‐isothermal Hele‐Shaw flows. The value of shear is derived for which the angular motion of the fiber in a quadratic velocity field is identical to that in a linear shear flow. Subsequently, numerical solutions for orientation distribution functions are presented for cases where analytical solutions for distribution functions are not obtainable. The rheological properties are then studied, using the orientation tensor description, for nonhomogeneous flow fields where the fiber motion can be approximated by that in a shear flow, the equivalent shear rate obtained from the numerical scheme.

Flow‐Induced Orientation in Monodomain Systems of Polymeric Liquid Crystals

Detailed numerical calculations are used to evaluate the orientational distribution function of monodomain polymeric liquid crystals in simple shear and elongational flow. Doi's theory of concentrated solutions of rigid rods is used to model monodomain systems of nematic PLCs. In addition, an analysis of the validity of the closure approximation in Doi's theory is presented. A novel numerical technique is presented for the solution of the distribution function. This technique can also be applied to the evaluation of other distribution functions encountered in polymer or fiber suspension rheology. Results from the numerical calculations are presented as a function of the rod concentration for different flow kinematics. Qualitatively, agreement between the decoupled elastic stress and the exact values is good, but quantitatively, there is some discrepancy.

Polymer solution and fiber suspension rheology and their relationship to turbulent drag reduction

It is shown that the rheological behavior of dilute polymeric solutions can be described, at least semi-quantitatively, by means of an equation containing a single viscosity coefficient and a single time constant. This expression and the Batchelor equation for suspension rheology are used to predict the major drag-reduction phenomena observed experimentally. It is shown that mixed polymer-fiber systems may be much more effective in their drag reduction capabilities than is either kind of additive when used alone. This latter prediction finds its qualitative verification in drag coefficients which are several-fold lower than those observed at the asymptote of ’’maximum’’ drag reduction in polymer solutions.

Rheology of Concentrated Suspensions of Fibers in Tube Flow. II. An Exploratory Study

The viscosities of concentrated suspensions of glass fibers in high viscosity silicone oils were measured with a 14″ capillary viscometer. Suspensions were mixed by various techniques, but only data for extruder mixed suspensions are presented. All pertinent suspension parameters were monitored, including wall effects. Yield stresses, squeeze-through, and capillary entrance exclusion were observed. Both the quantitative and qualitative aspects of fiber suspension rheology depended strongly on fiber length, which is consistent with the variety of behavior reported in the literature. Controlling fiber length independent of changes in other suspension parameters is difficult.