Permeability characterization of dual scale fibrous porous media

The proper characterization of fabrics used in liquid composite molding (LCM) is integral to accurately model the flow through these porous preforms. The dual-scale nature of many fabrics has brought about a need for a methodology, which characterizes not only the bulk permeability of the preform, but the micro-scale permeability of the fiber tows. These two permeability values can then be used in LCM simulations that can separately track the bulk flow front progression and the saturation of the fiber tows in preforms that exhibit dual-scale porosity. A three dimensional simulation called liquid injection molding simulation (LIMS) has been developed at the University of Delaware that can predict the impregnation of the fiber preform with resin in closed molding processes such as resin transfer molding (RTM) and vacuum assisted resin transfer molding (VARTM). To address the dual-scale porosity, standard 2D or 3D mesh elements are combined with ID elements, which are attached at each node and represent the fiber tows. This implementation allows for the interactions between the bulk and micro flow, and can predict the saturation of the fiber tows, along with the movement of the bulk resin flow front. However, it does require two permeability inputs: one for the elements representing the bulk preform and another for the ID elements representing the fiber tows. A methodology is proposed to determine the bulk permeability and a parameter that is closely associated with the micro permeability of the tows for dual-scale fabrics. This is accomplished by comparing the inlet pressure profiles of one-dimensional constant flow rate injection RTM experiments with a simulation of flow in a dual-scale fabric. The methodology is validated and characterizations for four different fabrics are performed to demonstrate the versatility and limitation of the methodology. (c) 2006 Elsevier Ltd. All rights reserved.