Abstract
The present work discusses the impact of the back coupling of the fiber orientation distribution on the base flow and on the fiber orientation itself during mold filling simulations. Flows through a channel and over a backward-facing step are investigated. Different closure approximations are considered for modeling the flow-induced evolution of anisotropy. The results corresponding to the decoupled approach, in which the effect of fibers on local fluid properties is neglected, build the basis of comparison. The modeling is limited to a laminar, incompressible, and isothermal flow of a fiber suspension consisting of rigid short fibers suspended in an isotropic Newtonian matrix fluid. A linear, anisotropic constitutive law is used in combination with a uniform fiber volume fraction of 10% and an aspect ratio of 10. To evaluate the impact of back coupling and of different closure methods in view of the manufactured solid composite the resulting anisotropic elastic properties are investigated based on the Mori–Tanaka method combined with an orientation average scheme. Relative to the range [0, 1] the pointwise difference in fiber orientation between the decoupled and the coupled approach is found to be pm 5{%} in the channel and pm 30{%} in the backward-facing step, respectively. The viscosity and the elasticity tensor show both significant flow-induced anisotropies as well as a strong dependence on closure and coupling.
Highlights
1.1 MotivationThe addition of rigid short fibers into a polymer matrix is an established method in lightweight design [32]
It is necessary to consider the anisotropic viscous properties of the fiber suspension already during the mold filling simulations. This aspect is often absent in numerical simulations of the processing of fiber-reinforced composites, in which only the effect of the flow on fiber orientation is considered while the local modification of the suspension properties
It is clear that using different closure approximations leads to different fiber orientation states
Summary
1.1 MotivationThe addition of rigid short fibers into a polymer matrix is an established method in lightweight design [32]. One challenge of dealing with short-fiber reinforced polymers is the reliable prediction of fiber orientation distribution induced by the strongly heterogeneous flow process, which determines the final effective mechanical properties of the product [6,43,67]. In this context, it is necessary to consider the anisotropic viscous properties of the fiber suspension already during the mold filling simulations. It is necessary to consider the anisotropic viscous properties of the fiber suspension already during the mold filling simulations This aspect is often absent in numerical simulations of the processing of fiber-reinforced composites, in which only the effect of the flow on fiber orientation is considered while the local modification of the suspension properties.
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