Conference Paper

Numerical 3D Permeability Prediction Using Computational Fluid Dynamics

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Permeability measurements and prediction are one of the most critical parameters for LCM simulation and have been focused in research for many years. Experimental permeability measurements are time and material consuming, but necessary for today’s FEM simulation. Virtual permeability prediction is usually based on small mesoscopic RVE models or analytical approaches. Using these state of the art methods the transfer to large near-net-shape textiles is not applicable. In this study, based on a plain mesoscopic triaxial 12K braid model created with WiseTex, TexGen and PAM-Crash, a method for numerical permeability prediction using an open source CFD code is introduced. The dimensions of the plate are 15 x 15 x 1 mm containing one layer and a fibre volume content (FVC) of 33 %. Furthermore a second compacted mesoscopic model is introduced to show the differences in permeability results. The dimensions of the compacted plate are 15 x 15 x 2 mm containing three layers and a FVC of 50 %. A full-field fluid flow is simulated with a steady state semi implicit pressure induced solver (SIMPLE) of the software tool OpenFOAM. In a following step the 3D permeability tensor field is determined using Darcy’s equation and the calculated flow conditions. Challenges in meshing and permeability calculation are identified and possible solutions for near net shape structures are shown. The results are compared between the two mesoscopic models, to different approaches of permeability tensor field calculation and to real experiments. The latter are executed with a radial test bench, a constant infiltration pressure of 2 bars and a 12K triaxial carbon braid with a FVC of 32.7 and 49.1 %.

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... This allows the macroscopic permeability to be inferred in all spatial directions. Dittmann et al. [74] also performed multi-scale simulations for this purpose, in which the permeability was determined at the fiber level, and the position of the deposited rovings was simulated macroscopically following a braiding process [75][76][77]. ...
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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.
... Microscopic simulations are object of research for many years in the field of fiber-reinforced polymers (FRP),. Next to microscopic simulations of FRPs and permeability prediction of yarns [1], some filament based simulation approaches for the deformation of carbon fiber yarns are described in literature [2,3,4]. Although, the friction mainly describes the interaction of the filaments, the authors used values that were derived at yarn level or estimated [2,3,4]. ...
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The friction between carbon filaments has a big impact on the deformation of dry yarns. Therefore, to simulate the deformation of yarns on a microscopic level, it is very important to obtain the true friction coefficient at different boundary conditions. The stiffness properties of the yarns change when other parameters, such as the fiber volume content, the tension or the speed of the deformation, vary. Considering processes that combine the forming and the impregnation steps (e.g. wet molding), the resin additionally influences the friction. Presenting a newly developed experimental setup for the friction measurement between filaments is the focus of this paper. In particular, the influence of the normal force, the relative velocity, the angle between the filaments, the presence of unpolymerized matrix and its viscosity are investigated, using design of experiments..
... Discrete determined permeabilities are mapped on a two dimensional macroscopic finite element net and a liquid compression molding simulation is performed. This helps defining inlets, outlets and injection pressures in the real manufacturing process [3]. ...
... Somit soll einerseits eine optimale Fertigung, in der das spezifische Verhalten des verwendeten Materials berücksichtigt wird, gewährleistet und andererseits die Eigenschaften des finalen Bauteils detailliert vorhergesagt werden. [3]. ...
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A unit cell based Computational Fluid Dynamics model is presented for predicting permeability of multilayer fabric structures. In Liquid Composites Moulding processes, fabric lay-ups undergo significant manufacture-induced deformation, combining compression, shear, and inter-layer nesting. Starting from the configuration of un-deformed fabric, the deformation is simulated geometrically by accounting for self-imposed kinematic constraints of interweaving yarns. The geometrical modelling approach is implemented in the open-source software TexGen. The permeability tensor is retrieved from flow analysis in ANSYS/CFX, based on TexGen voxel models. Using only measured geometrical data for un-deformed fabrics, deformed plain weave fabric and twill weave fabric lay-ups were modelled and their permeability tensors predicted. Comparison with experimental data demonstrates the generally good accuracy of predictions derived from the proposed numerical method.