Semi-analytical formulation of effective permeability of a dual scale unidirectional fabric

Abstract

Liquid composite molding (LCM) simulations for processes such as resin transfer molding (RTM) and vacuum assisted resin transfer molding (VARTM) face serious challenges while modelling resin flow through dual scale fabrics such as bi-directional (BD) (stitched or woven) fabrics and triaxial fabrics as it requires characterization of two permeability values: inter-tow gap or bulk permeability and tow permeability. Conventional experimental methodologies can characterize the inter-tow gap permeability by tracking the wetting resin flow front; however, there is no closed form solution that gives an expression for effective wetting permeability due to the uncertainty in determining tow permeability explicitly. If one were to have prior knowledge of tow permeability, effective wetting permeability can be formulated that can reduce the effort of experimental characterization. The current study proposes closed form permeability model for dual scale unidirectional (UD) fabric that combines both the tow and inter-tow gap permeability while taking into account the effect of partially saturated zone during dual scale flow. Thus, it accounts for the effects of inter-tow gap permeability, tow permeability and length of partially saturated zone. Comparisons of the analytic model results with numerical simulations are presented that are encouraging.