Co-authors​ :

 Tim SCHMIDT (GERMANY), David MAY (GERMANY) 

The permeability is a crucial material parameter required for the filling simulations and quantifies the conductance of the fiber structures for fluid flow. Numerous studies have already addressed the modeling and the numerical permeability prediction of composite structures. This has resulted in a variety of approaches for modeling of the fiber structures on the microscale, i.e. within fiber bundles, and the mesoscale, which deals with the textile structures. There are also different methods for calculating the dualscale permeability - taking the intra-yarn permeability into account for the calculation of the mesoscopic permeability. The model sizes and resolutions vary considerably and most structural models are referred to as representative volume elements (RVE), although this term is often incorrect. In addition to the RVE, the statistical representative volume elements (SVE) also appear in the literature. These 3D models are theoretically smaller than the RVE, as by definition they do not have to be representative for the entire structure with one model. This enables the use of models that are often more efficient to calculate. However, this requires that multiple randomized models should be simulated in order to determine representative material parameters for the structure. Apart from appropriate model sizing, structural models must encompass all pertinent features influencing permeability, such as fiber diameter and undulation in microscale models, or roving cross-sectional area and undulation in mesoscale models. The wide range of modeling strategies in the literature has led to the fact that no method has yet been able to be established and almost every player in this field is pursuing its own approach.
In this talk, the methods of how to develop statistically representative volume elements (SVE) for micro- and mesoscopic permeability prediction for textile-based fiber structures will be presented. These results are based on a large number of parameter studies performed with several thousand microscopic and mesoscopic models and tens of thousands of flow simulations. Beside the development and validation of the SVE the results of parameter studies to investigate the influence of individual structural features on the permeability are shown. Furthermore, methods and results for coupling micro- and mesoscale to dualscale simulations are presented. Finally, these investigations culminate in guidelines for modeling textile-based fiber structures for numerical permeability prediction, covering the entire process from structural modeling to permeability determination and result evaluation.