RTM Processes Research Articles

A dynamic data driven application system for real-time simulation of resin transfer moulding processes

This paper presents a numerical solution to optimize RTM processes based on a DDDAS methodology, taking permeability as stochastic. The model proposed in this investigation allows real-time accurate prediction of the filling rate by adjusting the parameters with the on-line captured process data. The suitability of the proposed model was tested and validated under different process parameters variations like pressure and preform permeability.

Bayesian inversion algorithm for estimating local variations in permeability and porosity of reinforcements using experimental data

A novel Regularising Ensemble Kalman filter Algorithm based on the Bayesian paradigm was applied to RTM processes to estimate local porosity and permeability of fibrous reinforcements using measured values of local resin pressure and flow front positions during resin injection. The algorithm allows to detect locations of defects in the preform. It was tested in virtual experiments with two geometries, a two-dimensional rectangular preform and a more complex 3D shape, as well as in laboratory experiments. In both the virtual and laboratory experiments, it was demonstrated that the proposed methodology is able to successfully discover defects and estimate local porosity and permeability with good accuracy. The algorithm also provides confidence intervals for the predictions and estimations of defect probabilities, which are valuable for analysis of the process.

Modelling of filtration of liquid binder in the composite textile structures under RTM processes

The paper deals with three-scale modelling of the filtration of a weakly compressible liquid binder in the tissue material of the filler in the production of composite materials based on the RTM method. The technique is based on the application of the asymptotic homogenization method for the Navier-Stokes system of equations. Local filtration problems for the threads level and for the monofilaments level are obtained.

An Investigation on the Quality of the Laminates Produced by VARTM Process and Process parameters

The production of FRP components by conventional manufacturing processes cannot provide assurance for repeatable quality, than the role of automation came to the FRP manufacturing industry in the form of RTM and VARTM processes, however the influence of process parameters such as permeability of pre-form and degree of vacuum to be applied for closed mould has significant influence on the end product quality. The quality of the laminate can be measured with the mechanical properties of the laminate produced at various process parameters. The present work consists of preparing the laminates of varied qualities produced by varying processes parameters in VARTM processes. The laminates produced were subjected to impact as per ASTMD standards. Further SEM Fracto graphs analysed thoroughly to understand the failure mechanism. The experimental results were co-related to identify a set of process parameters to produce sound FRP components in all respects.

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.

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.

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.

Preform-based toughening technology for RTMable high-temperature aerospace composites

This article describes the efforts that led to the development of surface-loaded preforms that may be used to significantly improve the compression-after-impact strength of high-temperature composites and correspondingly to dramatically reduce the area of damage because of impact. Moreover, by matching the toughening polymer surface-loaded and design of the surface pattern, in-plane mechanical properties are unaffected or even improved over laminates made from the identical materials. The proprietary preforms, so-called ES™-Fabrics, may be handled and infused with the high-temperature RTMable resins such as bismaleimide and polyimide in exactly the same manner as traditional fabrics without surface modification. The RTM conditions for the preform-based toughening is fully compatible with the traditional process procedure, making the technology cost-effective in production. This technology represents a key enabler for the use of low-cost RTM processes for high-temperature resins to supplant prepreg as the building-block material of choice for aeronautical composite structures.

Hyperelastic model for large deformation analyses of 3D interlock composite preforms

Abstract A hyperelastic constitutive law is proposed to describe the mechanical behaviour of 3D layer to layer angle interlock composite reinforcements. The objective of this model is to simulate shaping of thick textile preforms for RTM processes. After the identification of the independent deformation modes of initially orthotropic reinforcements, a strain energy potential is built up based on strain invariants representative to those modes assuming an additive composition of them. The parameters of the proposed constitutive model are identified using standard and specific mechanical tests performed on a 3D interlock material. Then, the model is validated on forming simulations on a single curve and double curve shapes. Three point bending tests on thick interlock reinforcements have been analysed experimentally and numerically. The specific transformation of cross sections is depicted by the proposed hyperelastic model.

Polyurethane structural adhesives applied in automotive composite joints

In recent years structural adhesives technology has demonstrated great potential for application due to its capacity to transform complex structures into solid unitary and monolithic assemblies using different materials. Thus, seams or joints integrate these structures providing, besides a reduction in weight, a considerable increase in the mechanical resistance and stiffness. The increase in the industrial use of structural adhesives is mainly due to their ability to efficiently bond different materials in an irreversible manner, even replacing systems involving mechanical joints. In the automobile industry structural adhesives have been widely used for the bonding of metal substrates, thermoplastics and composites, frequently employing these in combination, particularly glass fiber and polyester resin composites molded using RTM and SMC processes. However, the use of urethane structural adhesives in applications involving composites and thermoplastics has been the subject of few investigations. In this study the effects of temperature and time on the shear strength of RTM, SMC and ABS joints, applying temperatures of -40, 25, 80, 120 and 177 °C and times of 20 minutes and 500 hours, were determined. The objective was to evaluate the performance under extreme conditions of use in order to assess whether these joints could be used in passenger or off-road vehicles. The results showed that the urethane structural adhesive promoted the efficient bonding of these materials, considering that due to the high adhesive strength the failures occurred in the substrates without adversely affecting the bonded area. For each test condition the joint failure modes were also determined.

Investigation and Modeling of Compaction Behavior of Plain Fabrics

Fabric compressibility is very important in all RTM processes, and affects both the material and processing properties of the part. As the fabric is compressed by fluid pressure or the mold surface the fibers get compacted and the fiber volume fraction increases. This decreases the thickness of the part, decreases the permeability, and decreases the porosity. Compressibility is possibly more important to understand in one sided molding processes than in closed-mold processes. In this study, changing in permeability for four types of fibers that have been under pressure is measured. Based on experimental data related to permeability changes, for each type of fibers, plotted corresponding curves using interpolation and for each sample, modeled its behavior. Finally, the model outputs for several samples compared with experimental data to evaluate precision of model. The results showed that this model with low error can predict the permeability changes of fibers.

Simple models and optimization of compression resin transfer molding process

The optimization of the couplings between LCM processes and structural performances by repeated numerical simulations is expensive in terms of the computational cost. In order to overcome this difficulty, we propose a semi-analytical modeling of RTM and CRTM processes. Various processing routes of CRTM are considered according to the combinations of different stages of resin injection and reinforcement compression. This article is composed of two parts. First, we present analytical and semi-analytical models concerning the CRTM process with an imposed compression speed, in order to explain the methodology of resolution for the other CRTM manufacturing routes by an imposed compression force. The problems related to different constraints imposed on the CRTM process (imposed fiber volume fraction, feasibility criteria of process, and mold strength) are analyzed and formulated, so that they can be taken into account a numerical optimization. In the second part, a new numerical modeling of CRTM process with reinforcement compression under a force was developed and a comparison with semi-analytical model carried out. Recent work in the literature [Merotte J, Simacek P and Advani SG. Flow analysis during compression of partially impregnated fiber perform under controlled force. Compos Sci Technol 2010; 70: 725–733.] about the analysis of resin flow during compression of partially impregnated fiber preform under controlled force, allowed us to explore another alternative of comparison. Finally, this approach is used to control the RTM and CRTM processes and it is applied to a series of parametric studies, considering the effects of part size and fiber volume fraction on the mold filling time. This study not only contributes to the optimization of the couplings between manufacturing processes and structure, but also provides a tool for the control of the CRTM and RTM processes.

Edge effect in RTM processes under constant pressure injection conditions

AbstractIn resin transfer molding processes, the edge effect caused by the nonuniformity of permeability between fiber preform and edge channel may disrupt resin flow patterns and often results in the incomplete wetting of fiber preform, the formation of dry spots, and other defects in final composite materials. So a numerical simulation algorithm is developed to analyze the complex mold‐filling process with edge effect. The newly modified governing equations involving the effect of mold cavity thickness on flow patterns and the volume‐averaging momentum equations containing viscous and inertia terms are adopted to describe the fluid flow in the edge area and in the fiber preform, respectively. The volume of fluid (VOF) method is applied to tracking the free interface between the two types of fluids, namely the resin and the air. Under constant pressure injection conditions, the effects of transverse permeability, edge channel width, and mold cavity thickness on flow patterns are analyzed. The results demonstrate that the transverse flow is not only affected by the transverse permeability and the edge channel width but also by the mold cavity thickness. The simulated results are in agreement with the experimental results. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

On the Equivalent In-Plane Permeability

Simulation of RTM processes is usually performed in 2D. Thus, only a mesh of the middle plane is needed with the associated degrees of freedom savings with respect to fully 3D modeling. However such modeling needs the definition of an equivalent in-plane permeability representing the ignored dimension (the thickness). The definition of such permeability is not a trivial task because each ply in the thickness direction can be anisotropic, being the principal anisotropy direction different from one ply to the neighbor plies. In this work we propose a novel fully 3D modeling whose computational cost is equivalent to a 2D solution. It allows addressing properly the equivalent in-plane permeability issue.

Effect of Fiber Sizing — Test Fluid Interaction on the Unsaturated and Saturated Flow in the VARTM Process

The focus of this experimental investigation is the sizing-test fluid interaction reported to result in variable flow behavior in and permeability values for porous media. The flow behavior is studied for Vacuum Assisted Resin Transfer Molding (VARTM). Three types of sizing and three test fluids were chosen for the experiments. Two carbon stitch and two glass stitch bonded fabrics of different tow sizes were used for flow characterization. The present study uses two fluids with the same viscosity for each fabric to determine fluid-sizing interaction. The results show that the permeability values are the same with the fluids of same viscosity. The saturated flow behavior due to the heterogeneous nature of the media is different from the one observed in RTM processes. For VARTM processes the dual scale flow characteristics is not observed for a variety of tow sizes.

Effect of Fiber Sizing - Test Fluid Interaction on the Unsaturated and Saturated Flow in the Vartm Process

The focus of this experimental investigation is the sizing-test fluid interaction reported to result in variable flow behavior in and permeability values for porous media. The flow behavior is studied for Vacuum Assisted Resin Transfer Molding (VARTM). Three types of sizing and three test fluids were chosen for the experiments. Two carbon stitch and two glass stitch bonded fabrics of different tow sizes were used for flow characterization. The present study uses two fluids with the same viscosity for each fabric to determine fluid-sizing interaction. The results show that the permeability values are the same with the fluids of same viscosity. The saturated flow behavior due to the heterogeneous nature of the media is different from the one observed in RTM processes. For VARTM processes the dual scale flow characteristics is not observed for a variety of tow sizes.

Measurement of permeability of continuous filament mat glass–fibre reinforcements by saturated radial airflow

The measurement of fibre reinforcement permeability is important for the understanding, optimisation and modelling of RTM and resin infusion processes. This work investigates the use of a saturated radial air flow experiment for measuring the permeability of continuous filament mat (CFM), which is a common reinforcement type used for industrial RTM parts. The use of air, rather than liquid resin, is cleaner, quicker and potentially easier to control. The paper considers the problems inherent in using a compressible fluid, instead of a liquid, for the measurement of permeability, and the requirements for maintaining laminar flow. It describes the instrumentation used for flow and pressure measurement, and the effect of varying flow rate. Results compare favourably with published permeability values based on liquid flow experiments, and are independent of flow rate within the range of values investigated.

Effective mould release for RTM processes

The RTM process offers a challenge to mould release technologies because of its particular features. Fernando Castro of Zyvax explains this challenge and outlines a solution.

Analytical Modeling of CRTM and RTM Processes. Part I: General Mathematical Development

Analytical Modeling of CRTM and RTM Processes. Part I: General Mathematical Development

Analytical Modeling of CRTM and RTM Processes. Part II: Applications to the Analysis of the Process

Analytical Modeling of CRTM and RTM Processes. Part II: Applications to the Analysis of the Process