Resin flow in fiber preforms

Abstract

In a number of manufacturing processes for composite structures, resin flows through fiber reinforcement that is prearranged in a mold or a die. This article presents a review of mathematical models used to study the flow of resin through fiber reinforcement. The general approach is to consider the resin as a fluid propagating through a porous medium: the mold (or die) cavity partially filled with fiber reinforcement and other filler material. The resistance of the reinforcement to fluid flow is characterized by the permeability tensor and many analytical, numerical, and experimental techniques have been developed to predict or to measure the components of that tensor. The behavior of the resin depends on its viscosity, which depends on temperature and the degree of cure. Often mold filling is completed before any appreciable temperature change or curing occurs, so the analysis of this phase of the process is uncoupled from the thermal and curing problems. In other cases all three problems are coupled and should be solved simultaneously. Several complicating factors must be considered: 1) the deformation of the reinforcement during the preforming stage, during mold closure, or during resin injection, can affect permeabilities and flow patterns; 2) gaps between the reinforcement and the surface of the mold can cause edge flows that bypass the expected flow pattern; and 3) the inhomogeneous nature of the reinforcement with higher flow resistance inside fiber bundles than in surrounding gaps leads to complex flow patterns near the flow front and to the formation of microvoids. This article reviews the mathematical models that are required in order to simulate composite manufacturing processes in which resin flows through fiber reinforcement. The numerical implementation of these models using the finite element method or other numerical techniques is beyond the scope of this review. The bulk of the current body of knowledge in this area was developed since 1990. There are 165 references in this review article.