RTM Process Research Articles

Towards a 2.5D geometric model in mold filling simulation

Resin Infusion (RI) process is frequently used for large composite parts production. This Liquid Composite Molding method uses vacuum pressure to shape a plastic bag as a counter mold. Once a complete vacuum is achieved, the resin is sucked into a dry preform textile laminate via placed tubing. In this note we introduce a 2.5D model for a Liquid Composite Molding LCM process starting from a recent one introduced by Besson and Poussin in Besson and Pousin (2005) for the Resin Transfer Molding RTM process. Moreover for 2.5D models defined over quadrilateral reference domains, we show the effectiveness of the use of the Proper Generalized Decomposition. Finally, we propose a procedure, for a particular class of 2.5D model, in order to perform a numerical simulation of a mold filling process.

Epoxy resin and release agents part I: Inflence of external and internal release agents on the adhesive properties of epoxy resin

A wide range of epoxy resins are molded to produce composite components for various applications. Release agents are generally used to facilitate the removal of the component from the mold. The work presented in this paper shows differences between release agents and resin during a RTM process. Adhesive properties of release agents in interaction with the resin are analyzed, with respect to pressure and temperature. It was found that the reaction of epoxy resin results indifferent breakaway forces from mould surfacesdepending on used agents.

Improving Strain Field Measurements for Textile Composites

In this paper, an algorithm based on linear regression in conjunction with the periodical nature of textile composites for improving the strain fields measured by DIC and ESPI techniques is presented. Specimens of textile composites were prepared with regular stacking of layers using vacuum assisted RTM process and then tested under tensile loading within the elastic region. The improvement of strain fields determined by the proposed algorithm is illustrated and the applicability of which is discussed.

Numerical study of filling strategies in vacuum assisted resin transfer molding process

Abstract During the filling process of vacuum assisted resin transfer molding (VARTM), the infusion pressure gradient causes the resin flow and preform thickness variation. Even after the resin infusion discontinues, the resin keeps on flowing until the unnecessary resin is removed. In this study, a one-dimensional flow model coupled to the preform deformation is numerically analyzed to assess the influences of various processing scenarios on the infusion and post-infusion stages. The numerical model is implemented using a finite difference method. Results show that two strategies effectively reduce the filling process. One is to infuse less excess resin and the other is to turn the inlet into the additional vent. For a typical process using a one-sided vent, the theoretically optimum scenario is to infuse the exact required resin volume into the preform. From a practical standpoint, excess resin infusion is inevitable and a robust scenario is proposed by integrating the concept of fully filled preform and two strategies. Additional cases are performed using a vacuum assisted compression RTM (VACRTM) process for comparison purposes. Through the numerical work, a tool for optimization of the VARTM process is provided to reduce the filling process, resin waste and variability in the final composite part.

A mathematical model for RTM process simulations in geometries with irregular shapes

Composites made by using RTM processes have attractive properties to aerospace and automotive industries. However, it is mandatory optimize all process parameters. Some mathematical models developed to predict fluid flow in porous media may be used as a support tool for laboratory studies. These models present complex sets of differential partial equations that may be solved numerically, via discretization methods. This work presents a mathematical model to predict resin and air flow in RTM processes. The finite volume method was used to discretize the equations written in boundary fitted coordinates, without the need for any front tracking algorithm. To validate the methodology, numerical results for flow front positions in rectilinear flows were compared to analytical data. The model was also employed to describe the fluid flow in geometries with arbitrary irregular boundaries.

Evidence of thermo-oxidation phenomena occurring during hygrothermal aging of thermosetting resins for RTM composite applications

This paper focuses on the humid aging of a high temperature thermosetting resin employed for the realization of aircraft parts manufactured by the RTM process. Accelerated humid aging at several different temperatures (40–90°C) and relative humidity values (50–100%) has been carried out by means of gravimetric tests. Anomalous behavior with respect to Fick’s diffusion law and a color gradient from the edge to the center of the samples has been observed. Drying of samples after aging and mechanical tests on aged and dried samples have shown the existence of irreversible phenomena taking place during humid ageing: uniform tensile tests revealed resin embrittlement, Ultra Micro Indentation tests allowed measuring a gradient of properties from the surface to the centre of the samples. This behavior – associated to the color changes observed on aged samples – indicates that oxidation phenomena take place during hygrothermal aging.

Analysis of Composite Reinforcement at Mesoscopic Scale from X-Ray Microtomography

During the pre-forming stage of the RTM process, large deformations can occur, especially for double-curved shapes. Knowing the mechanical behaviour and the actual geometry of fibrous reinforcements at the mesoscopic scale is of great importance for several applications like permeability evaluations. As such, forming modeling is particularly demanding on the quality of geometric modeling and of the mesh associated. Indeed, analysis of the internal structure of materials in general, and woven materials especially, recently led to major advances. X-ray Micro Tomography (XRMT or μCT) allows detailed and accurate 3D observations inside the sample, which is not possible with the standard microscopy techniques restrained to surface observations. It distinguishes the yarns and even the fibers that define the directions of anisotropy of the material. A FE model is generated from the processed tomography images. It has been chosen in this study to use hypoelasticity behaviour law. Indeed, the yarns are submitted to large deformations, so that the orientation of the material is significantly modified and the fiber direction has to be strictly followed in order to fulfil the principle of objectivity. A way to retrieve the neutral composite reinforcement axis by skeletonization is proposed in order to know the privileged direction of the yarn and thus implement it in the constitutive law. A comparison between experimental and simulations obtained from μCT and idealized geometry of a transverse compression test on the G0986 is presented.

Modelling and Simulation of Resin Transfer Moulding: A Finite Volume Approach Applied to the Mold Filling Stage

RTM process is widely used for the production of high quality fiber reinforced composites parts. Computer simulations can play an important role in optimization of RTM processes by reducing risks and costs. In this paper, we present a two dimensional mathematical modelling for the mold filling stage in RTM process. It was used a two phase model (air-resin) which neglects the capillary and gravitational effects and considers all phases incompressible. The set of partial differential equations, expressed in boundary-fitted coordinates, are discretized by using the finite volume method and solved using a fully implicit methodology and the Newton's method. To validate the methodology, numerical and experimental data of the filling time and flow front position along the process are compared and good agreement was obtained.

The Manufacturing Technology Research of Composite Resin Transfer Molding

The main requirements of preparation of composite materials in aerospace industry are affordable , highly automated and good quality control.To reduce the mold cost and shorten the production cycle, the aviation industry is focusing on weaving technology,advanced spread with technology, autoclave technology, injection process, advanced curing process;,all quality concept and thermoplastic process. The main principle of RTM process is laying reinforced material form in the cavity, in accordance with the requirements of performance and structure, injection equipment will be used by special resin system of closed cavity, mold has fastening , injection mould with peripheral seal and exhaust system, which ensures that the resin flow smooth out all the gas in the cavity side by side and infiltrating fiber thoroughly, it also has heating system, which is used as heating composite components of.curing forming.

Effects of Resin Injection Speed on the Bubble Content of Glass Fiber Laminate

In order to eliminate the bubbles during composites manufacturing, a special performance was designed. And the effects of the speed of the resin injection on bubble content were investigated. The results demonstrate that the speed of resin injection has distinct effects on the bubble content. When the speed of resin injection is slightly higher than the speed of capillary injection, the bubble content of the test pieces with latitudinal fiber bundles is more than the test pieces without latitudinal fiber bundles. But when the speed of the resin injection is slower than the speed of capillary injection, the bubble content of the test pieces with latitudinal fiber bundles is less than the test pieces without latitudinal fiber bundles. These results will provide a reference for the design of RTM process parameters.

Properties of Water-Soluble Core-Materials Applied for LRTM

Traditional RTM process were difficult to integrally manufactured Composite components with complicated internal structures because the metal molds are heavy and expensive. LRTM process and Water-soluble core-mould materials could be used to solve the problem due to their flexibility, mechanical properties and water solubility. In this paper, manufacturing process and properties of water-soluble core-materials were studied. Moreover, using Light Resin Transfer Molding (LRTM) process to manufacture a hollow-structure, made of carbon fiber reinforced polymer.

Identification of Forming Limits for Unidirectional Carbon Textiles in Reality and Mesoscopic Simulation

In several fields of engineering the use of carbon fibre reinforced material (CFRP) is increasing. Minimized weight due to CFRPs could lead to lower consumption of raw materials especially in the automotive area. The goal within the research project TC² is the decrease of costs and production time for composite materials. To achieve better performance to weight ratio and to get acceptable production conditions the draping of dry unidirectional textiles and a following RTM process is investigated. Due to the high degree of complexity of automotive structures the forming process is challenging. Gapping in the textile could appear at corners as well as wrinkling or flexion of the fibres. To be able to define the amount and direction of layers or patches it is necessary to know the limits of forming for unidirectional material and to be able to predict the behaviour of the textile during the forming process. For the definition of the process limits several draping strategies are performed on different corner blend geometries. The goal of that work is to define the critical gradient of the flange to get first failures such as wrinkling or gapping. It is also important to understand the influence of different draping strategies. Parallel to the experimental tests a mesoscopic simulation method using an approach with roving and sewing thread is developed and presented. It is able to predict the material behaviour in critical areas (gapping, wrinkling). Different Young’s moduli and failure criteria can be implemented for the two main directions as well as for the bending of the textile. A validation with the experimental results is performed with the aim to enable the prediction of the textile behaviour using simulation methods.

A surrogate model based evolutionary game-theoretic approach for optimizing non-isothermal compression RTM processes

The Compression Resin Transfer Moulding (CRTM) process is a variant of the traditional RTM process and permits significantly faster fill times. However, the design parameters of CRTM processes must be carefully chosen in order to reduce cycle time, capital layout and running costs, while maximizing final part quality. These objectives are principally governed by the filling and curing phases which are strongly coupled in the case of non-isothermal processes. In this work the composites manufacturing cycle is modelled as a static Stackelberg game with two virtual decision makers (DMs) monitoring the filling and curing phases, respectively. The model is implemented through a Bilevel Multiobjective Genetic Algorithm (BMOGA), in conjunction with the Cascade-Correlation Learning Architecture Neural Network (CCA-NN) for function evaluations. The obtained results are efficient with respect to the objectives of both DMs and provide the manufacturer with a diverse set of solutions to choose from.

Resin Transfer Molding Process: A Numerical Investigation

In the processing of high performance composite materials, the RTM process has been widely used by many sectors of the industry. This process consists in injecting a polymeric resin through a fibrous reinforcement arranged within a mold. In this sense, this study aims to simulate the rectilinear infiltration of pure resin and filled resin (40% CaCO3) in a mold with glass fiber preform, using the PAM-RTM commercial software. Numerical results of the filling time and fluid front flow position over time were assessed by comparison with the experimental data and a good accuracy was obtained.

Toward an optimisation of the reactive resin transfer molding process: thermo-chemico-mechanical coupled simulations

In a view of reactive RTM process optimization, a numerical strategy is proposed to perform simulation of the filling stage of such a process, including the numerous thermo-chemico-mechanical couplings involved. Numerical simulations are then performed illustrating the capabilities of the strategy and underlying the numerical features that have to be taken into account. Finally, in order to build virtual charts for processability windows definition, the possibility to combine this numerical strategy with a multiparametric solver is addressed.

Numerical simulation of RTM process using the extended finite element method combined with the level set method

Numerical simulation for resin transfer moulding manufacturing process is attempted using the extended finite element method combined with the level set method. The level set method is used to transport the resin flow front at each time step during the mould filling. Extended finite element method allows to obtaining a good numerical precision of the resin pressure near the resin flow front, where the gradient of the pressure could be discontinuous. The enriched shape functions of extended finite element method are derived using the level set values so as to correctly describe these shape functions with the resin flow front. In addition, the position of the resin flow front at each time step is calculated by an implicit characteristic Galerkin finite element method. Some examples are presented to validate our study in comparison with analytical or experimental results and to illustrate its industrial applications.

The Effect of Thermal Aging on Properties of Epoxy Resin

The epoxy resin casting made by RTM process, making use of FTIR, SEM, weight loss, bending strength test and analysis method to study on its thermal aging at 90°C for various durations to see the change of chemical structure, thermal weight loss, microstructure, mechanical property. The results show that: the epoxy resin at 90°C occurs only physical aging, weight loss retention rate exponentially decreased, micro topography showed typical cohesive failure, bending strength exponentially decline in aging, the bending strength retention rate is 93.72% after aging 13d, which indicates this kind of epoxy resin with excellent aging resistance.

Algebraic rectilinear model for multilayer resin transfer molding injection

An analytical model for the multilayer rectilinear injection applied to the RTM process has been developed. The model takes into account the permeability in both in-plane ( Kxx and Kyy) and transverse ( Kzz) directions of each layer of the reinforcement media and calculates the transverse permeability ( Kt) through adjacent layers. Porosity and thickness are set independent for each layer of the assembly. Mass balance of resin within the layers is used to develop an expression that estimates resin position ( xi) as a function of time ( t) independently of each layer. The resulting equation was solved using: (i) Numerical integration and (ii) algebraic integration of the simplified expression resulting in a closed expression for xi = xi( t). Results of both proposed methods were compared with the calculations performed using the PAM-RTM software for cases with three, five and seven layers and the maximum calculated error in all cases was less than 12%.

Selección de resinas de poliéster insaturado para procesos de transferencia de resina en molde cerrado

En este artículo se analizan tres tipos de resinas poliéster in-saturado comerciales de amplio uso en el mercado nacional y se evalúa su conveniencia de uso en procesos de transferencia de resina en molde cerrado (RTM), de acuerdo con criterios de visco-sidad y reactividad. Se compara la viscosidad de las resinas entre 15 y 50°C, así como la reactividad mediante curvas de curado a temperatura ambiente, con porcentajes de catalizador del 1, 1.5 y 2%. De acuerdo con los resultados se determinó que algunas de las resinas son susceptibles de uso en procesos RTM, por su apropiada viscosidad, estabilidad en la reactividad y su velocidad de curado. Estas características son de gran importancia al momento de seleccionar las resinas poliéster insaturado, de acuerdo con las condiciones del proceso en molde cerrado.

Improving the Compression Strength after Impact of RTM Composites by Interlaminar Thermoplastic Nonwoven Fabric

Based on the “ex-situ” toughening concept, thermoplastic nylon (PA) nonwoven fabric with high porosity was chosen as the toughening layer, and the interlaminar toughened composites were fabricated via RTM process. Compression strength after impact (CAI) properties were investigated as well as the toughening mechanism. The results indicated that there is no bicontinuous phase structures formed by reaction-induced phase decomposition and inversion. The PA nonwoven fabrics still kept the original structure in composites interlaminar, and formed a macroscopical bicontinuous structure with the matrix resin, which also showed remarkable toughening effect. The CAI value increased from 212MPa to 281MPa.