Conference Paper

Experimental Validation of Numerical Dual-Scale Permeability Prediction. FPCM - 14th International Conference on Flow Processes in Composite Materials, Luleå, Sweden, 2018

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Permeability measurements and predictions are one of the most critical parameters for LCM simulation and have been subject of research for many years. Experimental permeability measurements are time and material consuming, but necessary for today’s FEM simulation. Virtual permeability predictions are based on different models or analytical approaches but the validation with experimental results is lacking. In Dittmann et al. [1] [2] the prediction of dual-scale permeability values with porous yarns in OpenFOAM for the use in FEM filling simulations is already shown. In this study, based on multi-scale triaxial 12K braid models created with TexGen, PAM-Crash and OpenFOAM, a validation of numerical predicted permeability values is addressed. To validate the numerical values and flow characteristics a separation of scale is necessary. Microscopic RVE simulations were validated with a capillary rise test bench. Therefore the permeability of UD preforms in fibre direction and perpendicular was determined. The dual-scale mesoscopic simulations were validated with glass fabrics to visualize the flow characteristics at microscopic and mesoscopic scale. The macroscopic simulations at part level were validated with VARI experiments, in a radial permeability test bench as well as with analytical solutions, published by B. R. Gebart [3], A. C. Long [4] and T. G. Gutowski [5]. Literature [1] J. Dittmann, S. Hügle, P. Seif, L. Kauffmann and P. Middendorf. “Permeability Prediction Using Porous Yarns in a Dual-Scale Simulation with OpenFOAM.” ICCM21, Xi'an, China, 2017. [2] J. Dittmann, S. Hügle, P. Middendorf. “Numerical 3D Permeability Prediction Using Computational Fluid Dynamics.” FPCM13, Kyoto, 2016. [3] B. R. Gebart. “Permeability of unidirectional reinforcements for RTM.” Journal of Composite Materials, Vol. 26, No. 8, p. 1100-1133, 1992. [4] A. C. Long. “Process modeling for liquid moulding of braided performs”. Composites Part A: Applied Science and Manufacturing, Nottingham, 2001. [5] T. G. Gutowski, Z. Cai, S. Bauer, D. Boucher, J. Kingery, S. Wineman. “Consolidation Experiments for Laminate Composites”. Journal of Composite Materials, Vol. 21, Massachusetts, 1987.

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The use of innovative higher-performance highly reactive resin systems requires an enhancement of the established method of fiber impregnation (open bath) towards closed resin-injection pultrusion (CIP), due to the short pot life of the resin systems. The result is that the open bath is developed into a closed injection and impregnation chamber (“ii-chamber”). In this study, three parameters—resin viscosity, opening angle and opening factor at the injection point on the ii-chamber—are varied, each in three stages. For each set of parameters, a pultrusion trial is conducted and the process pressures in the ii-chamber and pultrusion die measured. This enables direct feedback via the process conditions of the as yet uncured composite. The data obtained are used to validate a newly developed simulation model. The model is based on Darcy’s law, which has been extended to take fiber movement into account and thus represent the resulting pressure increase in the die. The flexible ii-chamber and die concept enhance our understanding of the processes taking place in the die system. The sensitivity of the process pressures can be shown for the three influencing variables. The experiment shows that of the three influencing variables investigated, viscosity has the greatest sensitivity to pressure development. In general, it can be said that over the length of the pultrusion die system, the pressure level increases across the three measuring points.
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