Newtonian
Fluid (upper picture) -
Shear-thinning Fluid (lower picture)
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The objective of this project, which is funded by the
German Research Foundation (DFG)
is the development of a molding process simulation of liquid composite materials. During
this process, polymerizing monomers are in situ injected into carbon fiber layings.
The project is worked upon in cooperation with the
Institute for Composite Materials (IVW)
in Kaiserslautern. The IVW develops the
measuring technology and a pilot plant for infiltration experiments; the resulting
material and process parameters represent the foundation of the modeling which is
done by the Fraunhofer ITWM, and they are also used for the validation of the simulation
software developed on the basis of the models.
The viscosity of the original material is very important for the modeling: at the beginning
of the injection, it corresponds to the low level of water, increasing towards the end of
the process up to two hundred times its original value. Additionally, the initially Newtonian
character of the monomer adopts a structural viscous behavior during polymerization. The low
viscosity at the beginning causes high flow velocities which cannot be described by the Darcy
law any longer. The structural viscous case is neither covered by this law, which means that
modifications of the Darcy equations are required for both cases.
The modified Darcy equations, which are described on a centimeter scale (macro scale),
include parameters such as permeability, which is determined on a micrometer scale due
to the microstructure of the carbon fiber laying. The microstructure simulation developed
at the Fraunhofer ITWM allows for, e. g., the computation of permeabilities. The existing
rheology models of the
Lattice-Boltzmann code ParPac
, which has been developed at the
institute, are therefore extended by non-Newtonian models, such as the Cross model.
The figure on the left shows two flow simulations in a carbon fiber
structure. Higher speeds due to shear-thinning effects are clearly
visible in case of the non-Newtonian fluid. The permeability is
calculated by averaging the microscopic velocity field and can then be used
in the macro model.
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