Raymond Gauvin

Limitations of a Boundary-Fitted Finite Difference Method for the Simulation of the Resin Transfer Molding Process

Resin Transfer Molding (RTM) is a commonly used fabrication method for large parts of fiber reinforced composites. The reinforcement consists of fiber mats or woven rovings first laid inside a mold cavity, then catalyzed resin is injected through prop erly positioned injection ports. A numerical model based on Darcys law has been devel oped. It permits to simulate, by a boundary-fitted finite difference method, the filling of two-dimensional molds of arbitrary shapes. The resin pressure distribution and the resin front positions can be obtained at each time step. Calculated results on selected mold geometries are compared with the experimental observations and discussed with those ob tained by other investigators. Finally the experimental and computational limitations of the proposed simulation are pointed out and illustrated for particular examples.

Modeling the edge effect in liquid composites molding

In Liquid Composite Molding (LCM) processes such as RTM or SRIM, preformed fabrics are preplaced in the mold cavity. The mold is then closed and a liquid thermoset resin is injected. Since it is difficult to precisely cut the fiber preform to the exact shape of the mold, sometimes a gap exists between the preform and the mold edge. This gap, even small (1 or 2 mm), can create a preferential flow path for the resin which disrupts the filling of the mold cavity. Such flow perturbation is called the edge effect. With existing numerical simulation models it is possible to simulate an edge effect by locally changing the permeability. However, this is not satisfactory. The ideal case will be a model to predict the edge effect from the geometry of the gap and the porosity of the surrounding material. To respond to this need, this paper presents an analysis of the flow patterns using appropriate flow equations in the open channel and Darcys law in the porous medium. From this an equivalent porous medium is defined for the channel for which an equivalent permeability tensor can be computed. Two geometric models to predict the edge effect are presented. The first model is derived from the Navier-Stokes equation in the channel. In the second model, the flow is assumed to take place in an equivalent cylindrical channel as in Poiseuille flow. However, these models cannot cover all cases. To evaluate the applicability of these simple models, a parameter called the transverse flow factor is defined. For finite element flow simulation an equation to define the equivalent permeability of the first row of elements encompassing the open channel is given. Finally, experimental as well as simulation results are presented.

Directional Permeability Measurement of Deformed Reinforcement

This paper presents a method for the evaluation of the anisotropic permeability of deformed woven fabrics. In order to conform to complex shapes, the woven fabric must undergo a certain amount of deformation. This deformation disturbed the resin flow and the filling of the mold cavity in liquid molding processes such as resin transfer molding (RTM). It is important for computer simulations of the filling process to predict the change of directional permeabilities k, and k2 caused by the deformation of the fabrics. Several flow experiments were conducted on a nonstitched woven fabric with different deformation angles. The deformation affects the global permeability and the directional permeabilities k1, k2. At the same time, the principal permeability axes are shifted. The resulting permeability is related to the orientation of the fabric. This article presents characteristic permeability curves for the fabric JBMartin NCS 81053-A as a function of the shearing angle or, alternatively, of the resulting fiber fraction. It is possible to conclude that for the fabric tested, the shearing angle of the reinforcement will have a definite influence on the resin flow pattern.

Numerical Analysis of the Resin Flow in Resin Transfer Molding

This report presents a study of modeling of the resin transfer molding. A numerical model for resin transfer molding simulation has been developed on the bases of Darcys law and the numerical generation of boundary fitted coordinate system. The resin pressure distributions, the resin front positions and profiles can be obtained through the computer simulation to help in the mold design and the process control Calculated results on selected mold geometries are compared with the experimental observations and with those obtained by other investigators.

Simulation of Compression Resin Transfer Molding with Displacement Control

In this paper a mathematical model of two-dimensional resin flow through fiber reinforcements in compression resin transfer molding (CRTM) is presented. The preform is partially filled by resin during the injection phase. Then it is compressed by the mobile upper part of the mold. The resin flow in the fiber bed is governed by Darcys law according to the theory of flows in saturated porous media. The consolidation of the saturated preform is described by the total mass conservation equation. A filling algorithm based on resin conservation on a deformable grid is used to advance the flow front at each time step. Resin pressure and velocity are calculated by the finite element method. The accuracy of the model is verified by evaluation of the resin mass balance, calculation of the resin pressure and progression of the flow front in time. Comparison of predicted results with analytical solutions is also presented.

RTMFLOT: an integrated software environment for the computer simulation of the resin transfer molding process

The computer simulation of the injection phase in resin transfer molding (RTM) can help the mold designer to properly position the injection ports and the air vents, to select an adequate injection pressure, and to optimize the cycle time. The purpose of this article is to present RTMFLOT, an integrated software environment especially designed for the numerical simulation of the resin transfer molding (RTM) process. The main program modules are DATAFLOT, to evaluate the permeability of the preform, MESHFLOT, to produce a finite element mesh of the mold, FLOT, to compute the succes sive positions of the resin front, VISUFLOT, to visualize the numerical results, and HEATFLOT, to analyze the heat transfer phenomenon. The application of RTMFLOT to the design of a lawnmower hood is described in order to illustrate the various stages of the simulation process.

The Modeling of Pressure Distribution in Resin Transfer Molding

The resin transfer molding process (RTM) allows the production of large FRP parts. In this technique layers of reinforcements (mats, woven rovings) are inserted into the mold cavity and resin is injected to fill the closed mold. Cavity pressure distribution is the most important parameter to minimize leakage problem at the parting line, to reduce mold deformation and to assure a good quality part. In this paper, a simplified model applicable to unidirectional flow is proposed to predict that pressure. It is based on Darcys law for flow of liquids through a porous media. The permeability of the reinforcement which is a function of the glass content and characteris tic of each type of reinforcement, mat or woven roving, is evaluated. Effects on the model of parameters such as glass density, surface density of the reinforcement and number of reinforcing layers are examined. The mold and instrumentation used to collect data are described and preliminary results are presented for reinforcing mat.

Impact response of laminated composite plates: prediction and verification

Abstract Methods and procedures for predicting the impact response of laminated composite plates using a commercial finite element system are described. Results of element evaluation, procedure verification and a correlation study are presented and discussed. The need for a hybrid experimental-numerical approach and combined geometric and material nonlinear finite element analysis is identified. A methodology for the prediction of delamination (onset and growth) is outlined.

Variation of Mat Surface Density and Its Effect on Permeability Evaluation for RTM Modelling

Continuous fiber strands mats are often used in Resin Transfer Molding (RTM). This paper presents the results of an extensive experimental study where the varia tion of mat surface density was investigated on five commercially available mats. The in- plane permeability for all these mats was also measured and compared with models found in literature. Since none of these models gave a satisfactory prediction for all the mats, a new empirical model is proposed. This model, with a set of specific parameters for each mat, can easily be stored in the data bank of any RTM flow simulation software.

Fatigue Mechanisms Under Low Energy Repeated Impact of Composite Laminates

This investigation deals with the fatigue behaviour under low energy repeated impact (LERI) of quasi-isotropic graphite/epoxy composite plates. The damage growth during the test was monitored by ultrasonic C-scan imaging. The damage area plotted as function of the number of impacts displays a three stages pattern behaviour. Stage I corresponds to a matrix cracking of the region under the impactor, stage II corre sponds to a rapid delamination propagation and stage III to a slow delamination propaga tion. The relative extent and the damage growth rate in stage II increase with the impact energy E I. The number of impacts NIF corresponding to the transition between stage I and stage II is governed by an impact-fatigue curve in the form of EI = C log (NIF) + E 0 where E0 is the threshold impact energy that induces a delamination in one impact and C constant denoting the damage tolerance of the material.