Rheological and small angle neutron scattering investigation of shear‐induced particle structures of concentrated polymer dispersions submitted to plane Poiseuille and Couette flow<sup><b>a)</b></sup>

Laun, H. M.; Bung, R.; Hess, Siegfried; Loose, Werner; Hess, Op.; Hahn, K.; Hädicke, Erich; Hingmann, R.; Schmidt, F. W.; Lindner, Peter

doi:10.1122/1.550314

Cited by 277 publications

(146 citation statements)

References 0 publications

Supporting

Mentioning

138

Contrasting

Order By: Relevance

“…However, it should be noted that the matrix viscosity given include toughening particles for T700/M21. Since the volume fraction of particles at the prepreg surface is approximately 35%, it is expected that the actual matrix viscosity (without particles) is lower [15]. The crosshead rate was selected based on realistic forming rates during sheet forming (vacuum forming) of pre-stacked prepreg material, given a geometry where a relatively small part is doubled curved, i.e.…”

Section: Friction Measurementsmentioning

confidence: 99%

On the interply friction of different generations of carbon/epoxy prepreg systems

Larberg

Åkermo

2011

Composites Part A: Applied Science and Manufacturing

View full text Add to dashboard Cite

Using pre-stacked material that is formed as a first step in the manufacturing process offers reduced process cycle time for production of complex structural components. The forming is achieved by forcing layers to deform by e.g. intraply deformation and interply slippage, where the latter is the scope of this study. The prepreg-prepreg friction is experimentally determined for four unidirectional carbon/epoxy prepreg systems. The materials differ considering volume fraction of fibres, fibre stiffness and phase of thermoplastic toughener (solved or particles). The study shows large individual differences between the tested materials, where the material systems with particle tougheners seem to obey a boundary lubrication friction, while the other materials show hydrodynamically dominated friction. A large difference between the high and low friction materials, almost a factor of 10, correlates to trends seen in the herein performed surface roughness measurements. Vacuum as well as autoclave consolidated materials are tested.

show abstract

Section: Friction Measurementsmentioning

confidence: 99%

On the interply friction of different generations of carbon/epoxy prepreg systems

Larberg

Åkermo

2011

Composites Part A: Applied Science and Manufacturing

View full text Add to dashboard Cite

show abstract

“…For the simplest case of steady shearing, the low density behavior is known [3], but upon increasing the density the growing importance of particle interactions requires theoretical approximation [4,5], hinders simulations [6], and calls for studies of model systems, e.g. [7,8]. Of major interest is the arrest of the structural relaxation when approaching solidification for higher densities, which raises the question of how the imposition of steady shearing might interfere with glass formation.…”

mentioning

confidence: 99%

“…Therefore steady state quantities shall be determined by considering the structural relaxation under shearing and "integrating through the transient dynamics". Because Pe 0 ≪ 1, we expect ordering or layering transitions to be absent [7]; and as hydrodynamic interactions are presumed to play a subordinate role during the structural relaxation [5] we neglect these too, focusing solely on the Brownian contribution to the transverse (shear) stress.With t 0 the time passed since the start of shearing, the correlation function of fluctuations in variables f and g …”

mentioning

confidence: 99%

Theory of Nonlinear Rheology and Yielding of Dense Colloidal Suspensions

2002

View full text Add to dashboard Cite

A first principles approach to the nonlinear flow of dense suspensions is presented which captures shear thinning of colloidal fluids and dynamical yielding of colloidal glasses. The advection of density fluctuations plays a central role, suppressing the caging of particles and speeding up structural relaxation. A mode coupling approach is developed to explore these effects.PACS numbers: 82.70. Dd, 83.60.Df, 83.50.Ax, 64.70.Pf, The properties of dispersions under flow are central to their processing and technological use [1,2]. But especially the non-linear rheology is not yet well understood. For the simplest case of steady shearing, the low density behavior is known [3], but upon increasing the density the growing importance of particle interactions requires theoretical approximation [4,5], hinders simulations [6], and calls for studies of model systems, e.g. [7,8]. Of major interest is the arrest of the structural relaxation when approaching solidification for higher densities, which raises the question of how the imposition of steady shearing might interfere with glass formation. The linear phenomenology is familiar: a colloidal fluid possesses a viscosity and flows, while a colloidal glass characterized by elastic constants, only distorts under strain [1,2]. But the nonlinear rheology of glassy colloids, which exhibit a continuous slowing down of the structural relaxation due to particle blocking (the "cage effect") [1], is less clear. While the mode coupling theory (MCT) recovers the linear phenomenology of this fluid-to-glass transition from microscopic starting points [9], a nonlinear external driving introduces new time scales whose influence on (non-)equilibration is not understood, and has been addressed only in minimal models [10] or mean-field approaches [11]. Moreover, as the true nature of the glass is still uncertain, its behavior under shearing may provide broader new insights (as suggested by recent simulation studies [12,13]).Here we develop a first-principles approach for the simplest case of a disordered colloidal suspension under steady imposed shear, neglecting both many-body hydrodynamics and the resulting velocity fluctuations. We first identify some generic features in the yield properties of glass; approximations suggested by the MCT are then introduced in order to derive quantitative predictions.The system consists of N spherical particles (diameter d) dispersed in a volume V of solvent with imposed flow profile v(r) = κ r, where for simple shear with velocity along the x-axis and its gradient along the y-axis, the shear rate tensor is κ ij =γ δ ix δ jy . The effect of the shear rateγ on the particle dynamics is measured by the Peclet number The system is taken to be in quiescent equilibrium (γ = 0) at t ≤ 0 when averages . . . (γ=0) are the canonical equilibrium ones. Then at t = 0 + , the velocity profile is switched on instantaneously, so that the steady state distribution function Ψ s , which satisfies Ω (γ) Ψ s = 0, will be approached at long times, t → ∞. If Ψ s was known the st...

show abstract

“…In the field of colloids, in which the particle scales are of 100 nm, the dynamical changes taking place during extreme shear thinning are well characterized by the linear lines of molecules forming along the shear direction-the strings of molecules pack into a hexagonal lattice, when viewed perpendicular to the shear direction-and this is termed a ''string phase.'' [33] The current work demonstrates the possibility of forming a string phase on an atomic scale at a high shear strain rate.…”

Section: B Three-dimensional Casementioning

confidence: 96%

“…[33,34] For example, using synchrotron X-ray scattering techniques, Sirota et al [34] found that as the volume fraction of polystyrene spheres in the liquid mixture of methanol and water increases, the system undergoes structural changes from liquidlike to a colloidal crystal of, first, bcc and, then, fcc. Furthermore, the colloidal viscosity is also studied and is found to be strongly dependent on the applied shear strain rate, exhibiting Newtonian as well as non-Newtonian behavior.…”

Section: Discussionmentioning

confidence: 99%

On Cyclical Phase Transformations in Driven Alloy Systems

Lee

2007

Metall Mater Trans A

View full text Add to dashboard Cite

Cyclical phase transformations occurring in driven materials syntheses such as ball milling are described in terms of a free energy minimization process of participant phases. The oscillatory flow behavior of metals with low stacking fault energies during hot working is taken as a prototype in which a ductile crystalline phase sustains undulation in its free energy, due to the alternate succession of work-hardening and work-softening mechanisms. A time-dependent, oscillatory free energy function is then obtained by solving a delay differential equation (DDE), which accounts for a time lag due to diffusion. To understand cyclical transitions on an atomistic scale, work is extended to molecular dynamics simulations. Under shear deformation, a two-dimensional nanocrystal shows cyclical transitions between an equilibrium rhombus and a nonequilibrium square phase. Three-dimensional simulations show crystalline-to-glass transitions at high strain rates, but very high shear strain rates are found to lead to a latticelike network structure in the plane perpendicular to the shear direction, with strings of atoms parallel to the shear direction.

show abstract

Rheological and small angle neutron scattering investigation of shear‐induced particle structures of concentrated polymer dispersions submitted to plane Poiseuille and Couette flow^a)

Cited by 277 publications

References 0 publications

On the interply friction of different generations of carbon/epoxy prepreg systems

On the interply friction of different generations of carbon/epoxy prepreg systems

Theory of Nonlinear Rheology and Yielding of Dense Colloidal Suspensions

On Cyclical Phase Transformations in Driven Alloy Systems

Contact Info

Product

Resources

About

Rheological and small angle neutron scattering investigation of shear‐induced particle structures of concentrated polymer dispersions submitted to plane Poiseuille and Couette flowa)

Cited by 277 publications

References 0 publications

On the interply friction of different generations of carbon/epoxy prepreg systems

On the interply friction of different generations of carbon/epoxy prepreg systems

Theory of Nonlinear Rheology and Yielding of Dense Colloidal Suspensions

On Cyclical Phase Transformations in Driven Alloy Systems

Contact Info

Product

Resources

About

Rheological and small angle neutron scattering investigation of shear‐induced particle structures of concentrated polymer dispersions submitted to plane Poiseuille and Couette flow^a)