RTM Process Research Articles

Influence of voids presence on mechanical properties of 3D textile composites

Presence of the voids in final part made of textile reinforced materials is one of the main process-induced type of defects, which is governed by a set of manufacturing parameters. This work focuses on investigating the effect of voids on mechanical properties of the 3D textile reinforced composites. This study includes the following steps: manufacturing of composite plates with RTM process, mechanical analysis, and multi-scale material modeling. The internal structure has been characterized from μCT scans and scanning electron microscopy observations. The influences of micro- (intra-yarn) and meso- (inter-yarn) porosities are discussed. Anisotropic damage model has been implemented into Fast Fourier Transform solver for simulation of nonlinear response of the 3D interlock composite. Analysis includes the averaged stresses in different material phases (warp, weft, and matrix) and local concentration of stress/damage field near voids.

Experimental process pressure analysis for model-based manufacturing of composites by resin transfer moulding

An experimental study of the process pressure characteristics prevailing in an RTM mould during the preform impregnation stage is presented. The pressure data is analysed with respect to a superposition of preform compaction and hydraulic fluid pressure. A methodology is proposed to isolate the hydraulic fluid pressure from the preform compaction pressure involving knowledge about the compressibility behaviour of the reinforcing material. For this purpose, the preform compressibility and relaxation behavior was studied by means of transverse compaction tests on both, unsaturated as well as the saturated sample stacks. The resulting isolated hydraulic fluid pressure is finally compared with numerical predictions derived from flow simulations, revealing good overall agreement. The findings of this work will contribute to realize the concept of model-based processing of fibre-reinforced polymer composites by means of the RTM process.

RTM technology of woven spacer fabric reinforced sandwich composite panels

The polyester fiber was utilized to fabricate the woven spacer fabric on the common loom, and the sandwich panels were produced by resin transfer molding process (RTM). The parameter of RTM molding process was determined. The correct ratio of resin, curing agent and accelerator in RTM process is 100:86:1. The injection temperature is 65°C. Injection time is shorter than 2 hours. Flexure and flatwise compression of composite panels were tested. The experiment result shows: flexure property and flatwise compression property of the RTM composite panels are better than that produced by handle paste shaping process.

Overview of Preparation Methods for High Performance Composite Materials

This article summarizes the advantages and disadvantages of the RTM process and its products. Based on a comprehensive analysis and comparison of common methods for improving the performance of RTM products, the principle and characteristics of the compression RTM (CRTM) process are highlighted and summarized. The research status at home and abroad analyzes the CRTM process parameters and their effects on the properties of composite materials, and points out the development trend of the CRTM process.

Introduction of intra-tow release/storage mechanisms in reactive dual-scale flow numerical simulations

Classical dual-scale reactive simulations of the RTM process assume permanent intra-tow resin storage in the saturated domain. However, recent experimental investigations revealed that permanent storage is occurring only in a limited volume of the tows. In the remaining volume, fluid is released in the channels with a rate that depends on the architecture of the textile and on the fiber volume fraction. Based on experimental observations, a new model is proposed to refine the simulation of the high speed reactive RTM process: a simplified microstructural model is used to enable permanent and partial transient storage within the tows. Additionally, a new sink term is proposed to reproduce the kinetics of the convective tow-channel fluid exchanges in the saturated domain. After a state of the art on dual-scale and reactive flow, the experimental inputs of the study are presented. The new model is then introduced, validated and characterized using the experimental inputs. Additionally, the influence of the release mechanisms on a reactive dual-scale injection is estimated by conducting comparative single-scale, and dual-scale simulations with transient or permanent storage. The new model has been demonstrated to be appropriate to reproduce accurately the release mechanisms, and simulations reveal the interest of taking these release mechanisms into account to simulate reactive dual-scale injections with an increased accuracy.

Simulating Mold Filling in Compression Resin Transfer Molding (CRTM) Using a Three-Dimensional Finite-Volume Formulation

Light-weight structural components are increasingly made of continuous fiber reinforced plastics (CoFRP), but their mass production is still very expensive. Because of its high automation potential, especially the Compression Resin Transfer Molding (CRTM) process gains more and more attention. Numerical mold filling simulations help to optimize this process and can avoid expensive experimental studies. Here, we present a new method to simulate mold filling in CRTM using a full three-dimensional finite-volume (FV) method. In comparison to known finite-element (FE) methods, it contains a compressible two-phase/Volume-of-Fluid description of the air- and resin-phase. This approach is combined with a moving mesh to account for the change of cavity height during the process, which results in a change of fiber volume fractions and thus permeabilities. We verify the method by comparison to analytic solutions of the Darcy equation and to solutions of state-of-the-art mold filling simulation software. The presented method enables CRTM mold filling simulation of complex parts, which is shown in two application examples. Furthermore, this shows the potential of using FV-based tools to simulate mold filling in RTM process variants containing non-constant cavity geometries.

Transverse permeability determination and influence in resin flow through an orthotropic medium in the RTM process

Transverse permeability determination and influence in resin flow through an orthotropic medium in the RTM process

Applying CFD in Manufacturing of Polymer Composite Reinforced with Shape Memory Alloy via Resin Transfer Molding Process

This paper aims to study the manufacturing process of polymer composite reinforced with shape memory metal alloys by RTM process using ANSYS CFX ® software. The mathematical modeling consists of mass and momentum conservation equations applied to a metal mold with dimensions 0.3 × 0.3 × 0.002 m³ containing ten NiTi alloy wires 0.0005 m diameter. Results of the flow front position of the resin (polyester resin mixed with calcium carbonate particles), pressure, streamlines and resin velocity fields during the process are presented and discussed. We conclude that the addition of calcium carbonate resulted in increased resin viscosity and greater inlet pressure obtained at the entrance of the mold which resulted in short time to full fill the mold and the highest pressures at the NiTi alloy wire surface were obtained in the central region and near the mold entrance.

An Investigation on RTM Process Parameters and their Influence on Impact Failure Behavior of FRP Laminates

The FRP industry needs certain suitable process parameters to produce sound FRP components with repeatable quality. The present investigation performed experiments on resin transfer moulding for making glass polyester laminates in the controlled volume. Experiments were conducted on chopped strand mat reinforcement with the general purpose resin, with varying process parameters, such as injection pressure and volume fraction of the reinforcement. Specimens made of various process parameters were subjected to impact test as per ASTMD256 standard. Laminates were prepared with various resin injection pressures were assessed by a ASTMD 2734-94 for the voids formation due to flow of the resin through the complex fiber architecture of the perform by RTM process. The experimental results were analyzed to correlate these results with the process parameters. The fractured surfaces are analyzed with scanning electron microscope to assess the influence of defects like voids in the laminate and to correlate the experimental results of impact test. This paper publishes the conclusions drawn from this experimental work to arrive at best process parameters for best damage tolerance of composite laminate.

RTM 공정에 의한 탄소/페놀 복합재료의 제조 및 특성 분석

RTM 공정에 의한 탄소/페놀 복합재료의 제조 및 특성 분석

Compressive Behavior of 3D Woven Composite Stiffened Panels: Experimental and Numerical Study

The structural behavior and damage propagation of 3D woven composite stiffened panels with different woven patterns under axial-compression are here investigated. The panel is 2.5D interlock woven composites (2.5DIWC), while the straight-stiffeners are 3D woven orthogonal composites (3DWOC). They are coupled together with the Z-fibers from the stiffener passing straight thought the thickness of the panel. A “T-shape” model, in which the fiber bundle structure and resin matrix are drawn out to simulate the real situation of the connection area, is established to predict elastic constants and strength of the connection region. Based on Hashin failure criterion, a progressive damage model is carried out to simulate the compressive behavior of the stiffened panel. The 3D woven composite stiffened panels are manufactured using RTM process and then tested. A good agreement between experimental results and numerical predicted values for the compressive failure load is obtained. From initial damage to final collapse, the panel and stiffeners will not separate each other in the connection region. The main failure mode of 3D woven composite stiffened panels is compressive failure of fiber near the loading end corner.

Synergistic local toughening of high performance epoxy-matrix composites using blended block copolymer-thermoplastic thin films

A new block copolymer-thermoplastic dual toughening concept for high performance RTM6 epoxy matrix composites is elaborated through a comprehensive microstructural study of well-defined model systems. A blend of phenoxy and MAM (copolymer of poly(methyl methacrylate) and poly(butyl acrylate)) increases the toughness of the corresponding carbon fiber reinforced composite by 125%, a five-fold synergistic improvement over the situation where the tougheners are used alone at the same total concentration. Selective intercalation of blended toughener thin films in the preform gives rise to a diffusion-induced composition gradient during the RTM process, which generates a morphology gradient upon curing. The observed microstructures results from MAM self-assembly in the miscible mixture of phenoxy and the epoxy resin precursor, followed by reaction induced phase separation, forming wormlike micelles, interconnected micelles and co-continuous morphologies. The resulting microstructures activate different toughening mechanisms responsible for the observed synergy.

Modelling VARTM process induced variations on bending performance of composite Omega beams

Finite element simulation with cohesive contact is presented, to correlate the vacuum assisted RTM process and the bending performance of Omega beams. The model considers the process induced variations, including part thickness, resin rich pockets and voids. The bending performance prediction relies on cohesive contact to model delamination initiation and propagation. Computing efficiency is achieved by mesh scaling. The modelling approach applies to three variations of Omega beams with the different mode-mixture ratios. The finite element predictions result in a high degree of agreement with the experimental measurements.

Mechanical Characterization of Composites Manufactured by RTM Process: Effect of Fiber Content, Strain Rate and Orientation

HIGH PERFORMANCE COMPOSITES ARE EXPOSED TO SEVERE LOADING AND ENVIRONMENTAL CONDITIONS. IN THIS WORK, MECHANICAL PROPERTIES OF FIBERGLASS REINFORCED POLYESTER (FRP) MANUFACTURED BY RESIN TRANSFER MOLDING WERE EVALUATED. THE EFFECT OF THE STRAIN RATE ON MECHANICAL PROPERTIES UNDER THREE QUASI-STATIC TESTING CONDITIONS, FOUR FIBER CONTENTS AND SEVERAL ORIENTATIONS WAS STUDIED USING INSTRUMENTED TENSILE TESTS. A MODEL WAS FITTED TO PREDICT TENSILE STRENGTH, YOUNG€™S MODULUS AND SHEAR MODULUS AND THE FAILED SAMPLES WERE ANALYZED TO UNDERSTAND THE FAILURE MECHANISMS. THE RESULTS SHOWED THAT THE FITTED MODEL IS RELIABLE ENOUGH TO CONCLUDE ABOUT THE EFFECT OF THE FIBER VOLUME FRACTION AND THE STRAIN RATE ON THE MECHANICAL PROPERTIES. YOUNG€™S MODULUS AND TENSILE STRENGTH INCREASED WHEN THE STRAIN RATE IS HIGHER. TENSILE STRENGTH ALSO INCREASED WITH FIBER CONTENT (VF) UP TO V_F=41%. THE PREDOMINANT FAILURE MECHANISM IS FIBER RUPTURE FOR THE MAIN DIRECTIONS AND FOR THE OFF-AXIS DIRECTIONS, THE FAILURE MECHANISMS ARE FIBER PULLOUT AND DELAMINATION

Effect of fiber chemical treatment of nonwoven coconut fiber/epoxy composites adhesion obtained by RTM process

In this work untreated and alkali treated nonwoven coconut fiber mats/epoxy resin composites were manufactured using the resin transfer molding process. The alkaline solution removes some impurities present on fibers superficial layers and the effect regarding fiber/matrix adhesion were investigated by thermogravimetric analysis, dynamic mechanical analysis (DMA), scanning electron microscopy (SEM), ultrasonic C‐scan, and quasi‐static flexural test. Results show a removing of some amorphous fibers constituents, mainly waxes, extractives, and hemicellulose, revealing the fiber roughness surface but no initial degradation temperature changing. Regarding the composites, a similar interfacial adhesion was observed in both one through the results of SEM, DMA and quasi‐static flexural tests. The conclusion is that chemical treatment conditions applied on the fiber surface was been suitable to improve fiber roughness but did not the adhesion between coconut fibers mat and epoxy resin. POLYM. COMPOS., 38:2518–2527, 2017. © 2015 Society of Plastics Engineers

The Hybrid RTM Process Chain: Automated Insertion of Load Introducing Elements during Subpreform Assembling

Fiber reinforced plastics are increasingly employed in the automobile industry. The process chain of resin transfer molding offers one approach for realizing structural components made of fiber reinforced plastic in high quantities. In order to increase economic efficiency, automated solutions for the subpreform assembly are required. There is also the need for mechanically highly stressable and at the same time economical joining techniques for joining fiber reinforced plastics with metal. The following article shall provide an approach to meet both of these requirements.

섬유방향성을 고려한 복합소재 대차 프레임의 RTM 성형 특성 해석

섬유방향성을 고려한 복합소재 대차 프레임의 RTM 성형 특성 해석

Eco-Casting of Aeolian Blades and Solar Panels With Composites Materials Via RTM Technology

The technique used for manufacturing composite wind turbine blades and solar panels must be sure of environment-friendly. In order to achieve this objective, the closed mould manufacturing process that takes into account environment preservation and health protection besides assurance quality will be the subject of this article. The requirements of sustainable development and ecodesign are the objectives to be fulfilled with an acceptable degree of tolerance in relation to the new regulations and eco-standards.Keywords: composite materials; ecodesign; RTM process; permeability; sustainable development; renewable energy

Characterization of Metal Inserts Embedded in Carbon Fiber Reinforced Plastics

The use of fiber-reinforced-plastics (FRP) contributes to an efficient implementation of lightweight design due to their outstanding specific mechanical properties. The RTM process offers great design freedom and allows the integration of functional elements during manufacturing. Embedded metal elements, so-called inserts, can be used to deal with the load transfer to structural parts. These elements have distinctive characteristics in comparison to other joining technologies. For example, detachable connections can be established with the help of inserts. Due to the fiber continuity not being interrupted and, subsequently, the FRP parts not having to be drilled, there is no local bearing stress. This paper aims at the characterization of metal inserts in FRP parts. The parts are manufactured using the RTM process with a specially adapted RTM mold with exchangeable cartridges for different insert geometries. The inserts are made of metal sheets with welded bushings and are embedded during preforming. The cured FRP specimens are tested under different load conditions to evaluate their suitability for various fields of application. Furthermore, the diameter and thickness of the metal sheet of the insert as well as the thickness of the FRP are varied to identify their influence on the failure behavior and load capacity under tensile loads.

Lightweight Hybrid Composites of CFRP and Aluminum Foam

The lightweight potential of components made of fiber-reinforced plastic can be enhanced by use of sandwich composites. So far, limited dynamic properties of plastic-based foams have prevented the use of sandwich composites in machine applications. The combination of closed-cell aluminum foam (ALF) and carbon fiber reinforced plastic (CFRP) provides a solution to this obstacle. Aluminum foam is characterized by favorable damping properties with minimum weight and CFRP provides high strength and stiffness at similarly low density. This paper deals with the design of a hybrid sandwich composite and its interpretation by using customized FEM simulations.Producing this kind of a sandwich composite in an economic production process presents a major challenge. Thus, a method has been developed that prevents excessive penetration of the resin into the pores of the aluminum foam. A high volume fraction of the resin in the foamed sandwich core would increase density and negatively influence damping properties. The implementation of a barrier layer will avoid this penetration. A DoE was developed and RTM process parameters were varied with the objective of achieving the highest specific bending stiffness. In preliminary experiments the appropriate range of injection pressure, mold temperature, and pressure force was determined. Tests with a nonwoven fabric could prevent the resin from infiltrating into the aluminum foam. Mechanical properties of the sandwich composite are only marginally affected.A model was developed to calculate the obtainable sandwich composite properties. The calculation method considers both the characteristics of the aluminum foam and the CFRP anisotropy. Based on this model a reliable calculation of the applied load could be accomplished. The design of the sandwich composite was targeting at high stiffness and determination of the natural frequency. Parallel to calculations, tests on specimen were performed and the obtained results were included into the calculation as part of the material model.