Effect of fiber-mat anisotropy on 1D mold filling in LCM: A numerical investigation

The ID flow experiment is one of the most common methods to measure the saturated and unsaturated permeabilities as well as to study the unsaturated flow in liquid composite molding (LCM) processes used for manufacturing polymer composites. The effective permeability along a flow direction in an anisotropic fiber mat, which is a function of the principal components of the permeability tensor and the angle between the principal and flow directions, is based on the assumption of uniform ID flow in the mat. In the present paper, the validity of such unidirectional flow assumption is shown to depend on three factors, i.e., the fiber-mat aspect ratio, the anisotropy ratio (the ratio of the major and minor principal in-plane permeabilities), and the angle of the principal permeability direction. A mold-filling simulation for hard-mold LCM processes based on the control volume/finite element formulation is used to investigate how these three factors affect the 1D flow. A new algorithm for applying the uniform inlet-pressure condition prevalent in the 1 D flow mold under the constant-flow-rate injection is developed to match the actual conditions in the mold. Our numerical results show that the three aforementioned factors have significant influence on the inlet-pressure history as well as on the mold-filling pattern. Maximum deviations from the unidirectional flow predictions in the inlet-pressure history as well as the flow-front progress is seen when the principal permeability direction is at an angle of 45 degrees with respect to the flow direction; these deviations worsen with a decrease in the mat aspect ratio and with an increase in the anisotropy ratio. However, the inlet-pressure history remains linear and the progress of the average flow-front remains predictable by the ID flow theory.