Flow channels/fiber impregnation studies for the process modeling/analysis of complex engineering structures manufactured by resin transfer molding

Abstract

The success of resin transfer molding (RTM) depends upon the complete wetting of the fiber preform. Effective mold designs and process modifications facilitating the improved impregnation of the preform have direct impact on the successful manufacturing of parts. Race tracking caused by variations in permeabilities around bends, corners in liquid composite molding (LCM) processes such as RTM have been traditionally considered undesirable, while related processes such as vacuum assisted RTM (VARTM) and injection molding have employed flow channels to improve the resin distribution. In this paper, studies on the effect of flow channels are explored for RTM through process simulation studies involving flow analysis of resin, when channels are involved. The flow in channels has been modeled and characterized based on equivalent permeabilities. The flow in the channels is taken to be Darcian as in the fiber preform, and process modeling and simulation tools for RTM have been employed to study the flow and pressure behavior when channels are involved. Simulation studies based on a flat plate indicated that the pressures in the mold are reduced with channels, and have been compared with experimental results and equivalent permeability models. Experimental comparisons validate the reduction in pressures with channels and validate the use of equivalent permeability models. Numerical simulation studies show the positive effect of the channels to improve flow impregnation and reduce the mold pressures. Studies also include geometrically complex parts to demonstrate the positive advantages of flow channels in RTM.

Influence of injection gate definition on the flow‐front approximation in numerical simulations of mold‐filling processes

“…Figure 9 shows the numerical results from a three-dimensional model with a mesh density ratio of one and an injection radius deÿned with four nodes on a face of a brick element. From Equation (15), it can be seen that the accuracy of the results is acceptable.…”

Non‐isothermal ‘2‐D flow/3‐D thermal’ developments encompassing process modelling of composites: flow/thermal/cure formulations and validations

“…If the ÿll factor is taken to be zero in the unÿlled regions and unity in completely ÿlled regions, then in partially ÿlled regions, the value of is 0¡ ¡1. With the assumption of a thin shell-like mold cavity, where the x and y co-ordinates are deÿned as the planar directions of the part and the z co-ordinate is deÿned as the gapwise direction (Figure 2), the governing equation for the ÿll factor and the pressure ÿeld in the pure FE methodology [3][4][5][6][7] given by…”

“…The reason behind this shortcoming is that in the ÿxed mesh technique, the ow front is typically located by interpolating a nodal parameter, namely, the ÿll factor F, among the nodes of the ÿxed mesh, and as a consequence, the accuracy of such a calculation su ers with the coarseness of the mesh and the interpolation scheme used. The traditional CV-FE formulation has been one of the more popular methods used, which explicitly tracks the ow front in the ÿxed mesh category; although more recent e orts by Mohan et al [3][4][5][6][7] have since shown signiÿcant enhancements related to both computational and physically improved attributes via a viable alternative Pure FE implicit methodology. Other related e orts by Kanapady et al [8][9][10] also clearly demonstrated the superior computational advantages of the Pure FE techniques and the inability of the traditional CV-FE approach to complete analysis of large-scale practical problems within 'reasonable time'.…”

Process modeling of composites by resin transfer molding - Sensitivity analysis for isothermal considerations

“…Some of the methods include the marker and cell (MAC) approach [1,2] which has been employed in metal casting simulations, the volume of fluid (VOF) approach [3] also commonly used in metal casting simulations, the control volume-finite element (CV-FE) explicit approach, and the pure finite element (Pure FE) implicit approach by Mohan et al [4][5][6][7][8]. The pure finite element approach has proven to be of practical importance and with improved physical attributes when compared to the traditional approaches.…”