Dry Fiber Placement preforms bear the potential for efficient manufacturing of preforms for liquid composite molding processes in composites manufacturing. For efficient process design and thus short cycle times and low scrap rates, impregnation behavior has to be fully understood to enable efficient process design. Hence, in a research project funded by Deutsche Forschungsgemeinschaft (DFG), basic principles concerning impregnating these preforms is scrutinized. Besides analytical and simulative approaches efficient numerical simulation methods are used. In order to realistically model flow behavior, three scale levels have to be considered:
- Micro level flow describes flow in between single fibers, i.e. inside a roving or a comparable structure in which fibers are nearly aligned. Relevant lengths are typically in the range of a few µm.
- Meso level flow describes flow between rovings or fiber bundles. Relevant distances are typically in the range of a few mm or cm.
- Macro level flow describes flow on scale of the manufactured part with relevant lengths being in the range of cm or m.
A variety of approaches has already been developed to describe micro level flow, but when transferring these to meso level, description of pore space available for fluid becomes nearly impossible. Experimental approaches are usually applied to measure effects on macro scale as physical quantities are nearly not experimentally assessable on micro scale. State of the art simulative approaches use permeability values determined on macro scale for filling simulation of a tool (Figure 1).
Therefore, in the approach applied here, a simulation method is developed to be able to describe flow behavior in micro and meso level inside the preform and deliver input values for flow simulations being conducted with a numerical solver on generated fiber structures (Figure 2).
For the development of this method, boundary conditions and requirements on a representative volume element have been developed ensuring correct computation of flow behavior with the solver (Figure 3).
Using this method, flow effects within preforms as well as the influence of targeted structural variation can be tested for their relevance for total permeability. Derived results can be used in following works for the optimization of material behavior. The validation of simulative calculations with experimental results was already successful (Figure 4).
A free license of GeoDict software has been kindly provided by Math2Market GmbH for this research work.
The project "Fundamentals concerning Impregnation of Preforms manufactured by Dry Fiber Placement" is supported by Deutsche Forschungsgemeinschaft (DFG), funding reference: BE 6334/1-1.
Dipl.-Ing. Oliver Rimmel
Institut für Verbundwerkstoffe GmbH
Phone: +49 631/2017-228