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TRANSIENT DUAL-PHASE VOID PREDICTION IN MICROSCOPIC YARN MODELS WITH OPENFOAM.
Abstract
Permeability measurements and analytical solutions for permeability prediction in the area of endless fiber reinforced plastics have a long history and are used as input for state of the art FEM mold filling simulations. As published in the third permeability benchmark, experimental measurement of permeability still shows big variations (29 - 38 %) depending on different measurement techniques, test rigs and test procedures. It was shown that numerical solutions can support these results by modelling the fiber architecture at microscopic and mesoscopic scale. These approaches also proved to be capable of taking into consideration the dual-scale effect of intra- and inter-yarn flow in endless fiber textiles.
In this study, the ability of numerical approaches to predict void formation and void transport on microscopic scale will be shown. Afterwards, we will compare the numerical microscopic prediction with published experimental results. Additionally, we will present an approach to upscale the microscopic void volume content to a simulation of mesoscopic textile impregnation.
... •Alternatively, micro permeability can be determined via numerical simulations based on computer-generated microscale models using suitable assumptions. [34][35][36][37] Usage of such values as roving permeability in dual-scale simulation models were carried out by Dittmann et al. [38,39] and Chen et al. [40] The outer shape of the rovings determines the meso flow channel shape and hence accuracy of the results strongly depends on a realistic representation. Yet, many models are strongly simplified and, for example, provide constant roving cross sections and perfectly regular waviness. ...
Extensive experimental test programs are required for the characterization of textile permeability, which is essential for the design of liquid composite molding processes. In this study, an experimental–numerical approach is presented, aiming to partially substitute experiments by numerical simulations. This approach uses 3D microscale simulations to evaluate the permeability within rovings and attribute these values to statistical volume elements of the textile at the mesoscale. To further improve accuracy, a calibration method has been defined. In order to validate the functionality of this approach the permeability of a glass fiber woven and a non‐crimp fabric at fiber volume contents (FVCs) between 50 and 60% were predicted. For the non‐calibrated but virtually compacted models with FVCs of 55 and 60%, the deviation ranges from −27% to +42%. This seems acceptable considering the typical scatter in experimental tests, for example, a CV of 20–50% was measured in recent permeability benchmarks. The numerically determined permeability was then used as input for numerical filling simulations at part level (macroscale). The resulting filling times were then compared to results of simulations based on experimental input values.
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