A shell model for resin flow and preform deformation in thin-walled composite manufacturing processes

Abstract

The paper proposes a novel approach to model the in-plane resin flow in deformable thin-walled fiber preforms for liquid composite molding processes. By ignoring the through-thickness flow in large scale thin-walled components, the 3-D resin flow is simplified to an in-plane flow inside the preform by a specialized divergence theorem. Shell kinematics are used to describe the fiber preform deformation, and the compressible flow is modeled in the context of the free surface flow in porous media. For simplicity and efficiency, the normal stretch, which is driven by the internal fluid and applied external pressure, represents the fiber preform expansion and compression. As compared with full 3-D models, the proposed shell model significantly reduces the problem size, while it still represents the primary physical phenomena during the process. The effects of neglecting the through-thickness flow are illustrated in a numerical example that compares the flow for a set of preforms with different thickness. The model is demonstrated from the numerical example of the mold filling in a doubly curved thin-walled fiber preform. Due to the applied vacuum and the consequent resin flow motion, the relevant deformation of the preform is observed.

Modeling and Experimental Validation of the VARTM Process for Thin-Walled Preforms

“…In this study, the shell model in [46] has been validated with a VARTM process experiment on the thin-walled preform. The model considers the resin flow as a problem of multiphase flow in porous media.…”

“…To describe the kinematics of the thin-walled preform, we consider the configurations of the solid (preform) and fluid (liquid and air) in Figure 3. The thin-walled preform is considered as a single director shell surface Ω 0 with the normal N. Furthermore, we assume that the preform can compress or expand only along the director N, as discussed in [46]. To measure the deformation, we define the stretch λ as the ratio between the thicknesses of the deformed preform, h, and the undeformed preform, h 0 , i.e.,…”

“…In this study, the main focus is the VARTM process of thin-walled fiber preforms. Given the nature of thin-walled preforms, the through-thickness flow is omitted, as discussed in [46]. By making this assumption, we can reduce the number of degrees of freedom of the problem.…”

“…Thus, the fluid pressure, p, and the saturation degree, ξ, are strongly coupled, which makes the problem complicated. The Equations (13) and (14) are solved by using the finite element method as a boundary value and initial value problem developed in [25,46]. Figure 7 shows the staggered approach to decouple the problem.…”

“…Although the presented models can successfully replicate experiments, either some of the models cannot handle the complex geometry, or other models need further information of the through-thickness permeability that is difficult to measure; neither model can be easily applied to the process optimization. Because of the nature of the thin-walled preform, it is assumed that the through-thickness flow can be ignored, and the preform deforms only along the normal of mold, as reported in [46]. The shell model finally simplified the VARTM process to a problem of 2-D in-plane resin flowing in the 3-D deformable preform.…”