Resin Transfer Molding Research Articles

Mechanical response of glass/kevlar hybrid composite jackets for steel containers carrying hazardous materials to enhance safety

Fiber reinforced (FRP) composite materials have high strength-to-weight ratios and excellent corrosion resistance. Cost reduction manufacturing through methods like Vacuum Assisted Resin Transfer Molding (VARTM) is impressive. This paper deals with composite materials reinforcement of railway tank cars via VARTM to enhance safety, improve fuel efficiency, and reduce adverse environmental impact during derailments aligning with industry goals for safer, sustainable solutions in relation to new railway tank car safety standards. This study investigates different performance aspects of various fiber/fabric configurations (glass, aramid) used as reinforcement with vinyl ester or epoxy. Additionally, core materials like polyurethane and polypropylene have been researched to enhance energy absorption. Effects of through-thickness stitching on mechanical integrity are evaluated for improved puncture resistance. Testing revealed that Kevlar fibers increased energy absorption by increasing strain to failure. Epoxy resin lowered maximum tensile strength by 22% compared to vinyl ester and increased the total energy absorption by 8%. Through-thickness stitching (z-direction) increased tensile strength by 13% and improved interlaminar shear strength.

Graphene Oxide and Natural Silk as Reinforcements for Epoxy Resin Matrix: Fabrication, Sample Preparation, and Testing

The integration of graphene oxide (GO) and natural silk into epoxy matrices offers a promising approach to developing high-performance composites for structural applications. This study examines the fabrication processes, focusing on sample preparation and testing of GO and natural silk-reinforced epoxy composites. A comprehensive literature review spanning 1990 to 2024 provides insights into the necessity of Vacuum-Assisted Resin Transfer Molding (VARTM) at 30 PSI, the role of ultrasonication in achieving homogeneous GO dispersion, strategies to prevent agglomeration, optimal reinforcement proportions, and challenges encountered during hybridization. Key findings, including the impact of high silk volume fractions (60–70%) on mechanical properties, are incorporated, offering a comprehensive guide for composite fabrication. The findings underscore the critical parameters for successful composite fabrication and performance enhancement. Key Words: Graphene Oxide, Natural Silk, Epoxy Composites, VARTM, Ultrasonication, Hybrid Reinforcements, Structural Applications

Hybrid Composites: Graphene Oxide and Woven Natural Silk Reinforcement for Epoxy Matrix

The integration of graphene oxide (GO) and woven natural silk as hybrid reinforcements in epoxy composites offers a novel approach to high-performance, sustainable materials for structural applications. Combining GO (0.3–1.5 wt.%) and natural silk (40–60% by volume) is hypothesized to significantly enhance tensile strength, flexural modulus, and impact resistance. Fabrication using Vacuum-Assisted Resin Transfer Molding (VARTM) and optimized GO dispersion through ultrasonication addresses challenges like GO agglomeration and fiber-matrix adhesion. Although experimental validation is pending, Theoretical predictions supported by finite element modelling (FEM) suggest significant improvements in tensile strength, flexural modulus, and impact resistance compared to neat epoxy. These composites hold promises for structural applications in aerospace, renewable energy, and automotive industries, meeting the demand for lightweight and sustainable engineering solutions.

Comprehensive analysis of the effect of braiding angle on the wettability and mechanical properties of 3D braided carbon fiber fabric-reinforced composites

Fiber-reinforced composites are designed to enhance strength, stiffness, and lightweight properties. However, while the use of continuous fibers offer substantial performance benefits it presents challenges in achieving complex configurations. This study focused on evaluating the effects of different braiding angles on the mechanical properties of braided fabric-reinforced composites (B-CFRP). Continuous fiber tows were braided around a mandrel, with meticulous control over the key process parameters to ensure consistency. The composites were then processed using the Vacuum Assisted Resin Transfer Molding (VARTM) technique to achieve optimal impregnation of the resin. Mechanical properties, including tensile, flexural, compressive strength, interlaminar shear strength (ILSS), and impact strength, were performed to establish the relationship between resin impregnation and mechanical properties with different braid angles. Additionally, resin flow experiments and scanning electron microscopy (SEM) analysis were conducted to investigate how variations in braiding angle influence fiber arrangement, resin distribution, and fracture behavior. These insights aim to guide the design and manufacturing of high-performance composites.

Influence of carbon nanotubes on the absorption performance and mechanical behavior of basalt fiber composite materials

AbstractBasalt fibers (BF) are widely used in shipbuilding due to their excellent corrosion resistance. However, basalt fibers do not possess good electromagnetic wave absorption properties, failing to meet the stealth performance requirements of ships. Therefore, this study focuses on basalt fiber composite materials, modifying the matrix by adding different amounts of carbon nanotubes (CNTs). Carbon nanotube‐basalt fiber‐epoxy resin absorptive composite materials are prepared using Vacuum Assisted Resin Transfer Molding (VARTM) technique to investigate the influence of CNT content on the materials. Samples with added CNTs can effectively absorb electromagnetic waves in the low‐frequency range, reducing surface reflectivity. In the high‐frequency range, the impedance matching value of the samples initially increases slowly. When the CNT content reaches 1.5 wt%, at a thickness of 2.5 mm and a frequency of 9.6 GHz, the minimum reflection loss of the sample is −14.40 dB, with an effective absorption bandwidth of 0.7 GHz. Also, CNTs can enhance the mechanical properties of composite materials. With increasing CNT content, both the bending strength and tensile strength of the composite materials are improved. When the CNT content reaches 1.5 wt%, the average tensile fracture strength of the material increases by 21%, and the bending strength increases by 9%.Highlights Enhanced low‐frequency electromagnetic wave absorption from CNTs and reduced polarization. Improved impedance matching and attenuation at high frequencies with CNTs. Significant enhancement in flexural and tensile strength due to CNTs and basalt fibers.

On the Fabrication Processes of Structural Supercapacitors by Resin Transfer Molding and Vacuum-Assisted Resin Transfer Molding

This study investigated the manufacturing processes for structural supercapacitors (SSCs) using smear molding (RS), resin transfer molding (RTM), and vacuum-assisted resin transfer molding (VARTM). Woven carbon fibers were used as the electrode, woven glass fibers as an insulating layer, and an alkaline/epoxy compound as the electrolyte. In the RTM process, due to the vacuum and the high-pressure injection of the electrolyte, the electrochemical and mechanical properties of the SSC can be greatly improved, and the void contents in the SSC can be reduced. The balanced electrochemical performance and mechanical properties of SSCs were observed in the range of epoxy content from 15 wt% to 30 wt%. This study contributes to the development of SSCs through the establishment of the fabrication process for improvements in part quality. The fabrication method demonstrated here can be directly applied by industries to produce even larger-scale SSCs, opening up new possibilities for practical implementation and scalability.

An efficient ultrasound vibration strategy for suppressing intra-bundle pores and regulating pore morphology in carbon fiber-reinforced composites

The competitive resin flow between intra- and inter-bundles, always causes the generation of intra-bundle pores during resin transfer molding (RTM), thereby weakening composite mechanical performance. Accordingly, an ultrasound vibration strategy is originally developed to efficiently suppress and improve the spatial morphology and distribution of intra-bundle pores in RTM manufacturing. The effects of ultrasound vibration on the spatial evolution of intra-bundle pores are systematically investigated, furthermore, the suppression mechanisms of intra-bundle pores are revealed. Additionally, an empirical model that predicts porosity under ultrasound vibration, is established and well validated for the developed ultrasound vibration strategy, which provides a feasible path for effectively manufacturing composites. X-ray micro-computed tomography experiments verify that applying a short period of ultrasound vibration balances the dual-scale flow by regulating the modified capillary number, thereby significantly reducing porosity by up to 59.4 %. Numerical analyses indicate that the acoustic cavitation and acoustic flow induced by the ultrasound vibration, facilitate the collapse and transverse migration of larger bubbles, thereby remarkably suppressing the connected pores and larger pores. In particular, the ultrasound vibration strategy completely removes the pores larger than 300 μm. Besides, the collective effects of vibration, compression, and shear forces contribute to forming near-circular pores, which are beneficial for ensuring the expected mechanical performance of composites.

A New Approach for Improving Flame Retardancy of Automotive Interior Upholstery

This study presents the flame retardant (FR) performance of chemically treated automotive upholstery fabrics using two different impregnation methods of Resin Transfer Molding (RTM) and supercritical carbon dioxide (scCO2). Referring to the related standards, untreated seat fabric obtained from seat upholstery of a bus (neat fabric, NF) and treated fabric samples underwent burning rate (BR) and limiting oxygen index (LOI) tests to compare effect of treatment and impregnation methods on FR performance. Thermal analysis was also conducted on the samples considering onset degradation temperatures and char yields. The results showed that BR and LOI of all samples were in acceptable range and treatment provided enhancement in FR performance of NF. The treated sample using scCO2 method gave the highest LOI value of 32% and the lowest BR of 21 mm/min subtending to 18.5% increase in LOI and 30% reduction in BR compared to those of NF. The performance of treatment in RTM was worse than that of scCO2 and better than that of NF. The results confirm that both treatment and methods used in this study give promising results for safety against fire in transportation vehicles.

Curved surface coupled structural battery composites manufactured by resin transfer molding process: Microstructure and multifunctional performance

To bridge industrial production and lab-scale research, this work demonstrates a technology to manufacture curved surface structural battery composites (CSBCs) that can simultaneously achieve electrochemical energy storage and load-bearing. The curved-surface carbon fiber structural anode and cathode are fabricated by coating the active materials on carbon fiber fabric with a vacuum-bag-assisted technique. The resin transfer molding (RTM) process is conducted to manufacture the coupled CSBCs by infusing bi-continuous phase epoxy resin electrolyte and curing at high temperatures. The microstructure of structural electrodes and CSBCs is characterized by scanning electron microscopy (SEM). Due to good interfacial compatibility between high mechanical strength carbon fiber structural electrode and high ionic conductivity solid polymer electrolyte bulk for load support, the fabricated CSBCs demonstrate a high density of 294 mWh kg−1 based on the whole mass of devices, a tensile strength of 257.4 MPa with Young's modulus of 12.9 GPa and a flexural strength of 194.1 MPa with flexural modulus of 11.1 GPa. In situ electrochemical-mechanical tests further confirm the durability of CSBCs under mechanical loads with a multifunctional efficiency of 1.07, suggesting the effectiveness of the introduced manufacturing techniques for coupled structural battery composites.

Defect detection on RTM composite parts via robotic contact measurement system

In this work a new approach to detect and to evaluate defects typical of carbon fiber parts manufactured via resin transfer molding (RTM) is presented. The approach is based on a robotic contact measurement system, as an alternative or combined solution to vision methods. The research is meant to provide more accurate local geometry information to the global information acquired using vision systems. The system consists of a collaborative robot equipped with a force-torque sensor that scans the surface of the workpiece with a defined motion strategy. To evaluate the system, tests were conducted on a 3D printed part presenting a feature representative of the defects found on carbon fiber components. The results are compared with the CAD model and data acquired using a structured light scanner, showing that robotic contact measurement can be a viable method to enhance the reconstruction of a part with a higher accuracy. The system is then applied and validated on a real part made with RTM.

Impact response and compression-after-impact properties of foam-core sandwich composites incorporating scrap tyre rubber particles

Integrating scrap rubber particles as fillers into polymer matrix composites offers a cost effective and environmentally sustainable pathway to manage tyre waste through the creation of value-added products. This research explores the low-velocity impact (LVI) response and compression after impact (CAI) properties of rubberised foam-core glass fibre-reinforced epoxy (GFRE) sandwich composites. Syntactic foam cores integrated with rubber particles were manufactured using vacuum-assisted resin transfer moulding (VARTM). The compression properties of rubberised foam core, vital for resisting impact damage during LVI, were examined. Results show more than 40% reduction in compression strength and modulus of the syntactic foam upon the inclusion of 33 wt.% rubber particles. The LVI response and residual compression properties of rubberised foam-core composites were also evaluated. Rubberised foam cores caused a marginal reduction in the peak impact force and led to approximately 60% reduction in the delamination area. The pre-impact compression strength was unaffected by rubber particles within the core as the GFRE face sheets carried most of the compression load. Post-impact compression strength was slightly higher in rubberised foam-core composites due to reduced delamination. Digital Image Correlation (DIC) analysis tracking of the strain evolution during CAI experiments revealed the stress-raising effect of the impact damaged region. This study showcases sustainable scrap tyre management through the inclusion of rubber particles into foam-core composites without substantially reducing in-plane compression properties before or after low-velocity impact.

Additively manufactured resin transfer molding (RTM) plastic tooling for producing composite T-joint structures

Additively manufactured resin transfer molding (RTM) plastic tooling for producing composite T-joint structures

Induction heating simulation for aircraft RTM toolings

Aircraft CFRP parts as sharklets are produced in resin transfer molding (RTM) tooling. The parts need to be heated up homogenously over the whole area with a constant temperature. The complex shape and accessibility of the tooling make it hard to introduce a common heating system. In addition, the heat must be transferred through the Invar metal tooling structure onto the CFRP. Infrared lamp, air fan and microwave heating are concepts in development. Electrical heating layer mats and cages are laborious in applying. Induction has the advantage of contact-less, efficient, and fast heating. Induction heating was tested for the structural bonding of CFRP frames and stringers showing high bonding strengths. To apply this technology for the RTM tooling, the placement and distance of the induction coils is important. Simulation can help to find the right adjustments and power needed for induction heating. With the program COMSOL the surface and the coils are modeled, and the numerically structured net is divided in small tetrahedron and quadratic sub elements. Since there is no magnetic streamline in the middle of the coil-section, a symmetric halving of the structure is applied as a boundary condition. The temperature-time development and the distance of the coils are simulated in 2D and 3D. Due to the material properties of the magnetic flux concentrator (MFC), higher flux concentration of the magnetic field occurred only in 2D. The results are validated by experiments and are in good agreement.

Real-time Bayesian inversion in resin transfer moulding using neural surrogates

In Resin Transfer Moulding (RTM), local variations in reinforcement properties (porosity and permeability) and the formation of gaps along the reinforcement edges result in non-uniform resin flow patterns, which may cause defects in the produced composite component. The ensemble Kalman inversion (EKI) algorithm has previously been used to invert in-process data to estimate local reinforcement properties. However, implementation of this algorithm in some applications is limited by the requirement to run thousands of computationally expensive resin flow simulations. In this study, a machine learning approach is used to train a surrogate model which can emulate resin flow simulations near-instantaneously. A partition of the flow domain into a low-dimensional representation enables an artificial neural network (ANN) surrogate to make accurate predictions, with a simple architecture. When the ANN is integrated within the EKI algorithm, estimates for local reinforcement permeability and porosity can be achieved in real time, as was verified by virtual and lab experiments. Since EKI utilises the Bayesian framework, estimates are given within confidence intervals and statements can be made on-line regarding the probability of defects within sections of the reinforcement. The proposed framework has shown good predictive capabilities for the set of laboratory experiments and estimates for reinforcement properties were always computed within 1 s.

Thermoviscoelastic modelling of highly reactive thermoset resins for liquid moulding applications

This paper presents a methodology for developing thermo-mechanical properties model for highly reactive resins and its use for Resin Transfer Moulding process (RTM) modelling and prediction of residual stresses. Cure Hardening Instantaneously Linear Elastic (CHILE), and Thermoviscoelastic (TVE) models, were implemented to analyze the mechanical behaviour of the resin. Simulation of the RTM process was developed and applied to a representative curved plate geometry. An integral approach was considered where the degree of cure gradient, generated during the filling stage due to the reactivity of the resin, was implemented as initial condition of the stress-deformation process simulation. The validation process included fabricating experimental parts with the representative geometry. The degree of cure variation of highly reactive thermosets during injection caused a significant effect on the final shape of the parts. These effects were captured by the simulations, where the TVE model showed a more accurate prediction of the part distortion.

Surface Treatments' Influence on the Interfacial Bonding between Glass Fibre Reinforced Elium® Composite and Polybutylene Terephthalate.

This study examines the process of using injection moulding to join two different materials to manufacture bi-component moulded products with improved performance characteristics. The two-component process, which combines the advantages of two different technologies-the high efficiency of the injection moulding process and the excellent mechanical properties of long glass fibre composites produced by resin transfer moulding (RTM) technology-offers a particular advantage and improved applicability of the prepared lightweight products in both the automotive and aerospace sectors. The composite studied here consists of Elium® thermoplastic resin (30%) reinforced with unwoven glass fibre fabric (70%) using the RTM process. The Elium® composite sample is consequently used as an insert overmoulded with polybutylene terephthalate (PBT) homopolymer reinforced with 20% w/w of short glass fibre through injection moulding. The influence of different mould temperatures and surface treatments on the adhesion between the materials used is investigated by evaluating the mechanical performance using tensile shear strength tests. It was found that while an increase in mould temperature from 40 °C to 120 °C resulted in a doubling of the initial average bond strength between untreated Elium® RTM inserts and overmoulded PBT parts (0.9 MPa), sandblasting the inserts ensured a further tripling of the bond strength of the composites to a value of 5.4 MPa.

Optimization of the VARTM Process for Prototyping a Bumper Using Hybrid Composite Materials

To provide an alternative for manufacturing auto parts using composite materials, the Vacuum Assisted Resin Transfer Molding (VARTM) process was utilized to prototype the bumper for the Chevrolet Aveo vehicle. This technique emerges as an alternative for composite material manufacturing, allowing for rapid and high-quality production of advanced composites. In this study, a hybrid composite material reinforced with fiberglass, cabuya fiber, IN2 epoxy resin, an infusion mesh, peel ply, and a vacuum bag was employed. To optimize the VARTM process in bumper prototyping, several simulations of resin flow were conducted with different locations of resin injection and vacuum entry points. Autodesk Moldflow Insight software facilitated the modification and addition of resin injection points to observe the flow evolution, thus determining the filling time for each proposed design. Six different designs were applied for the bumper mold filling. The proposed linear flow design reduced the total filling time of the bumper mold by 81.56% compared to the other five designs analyzed. The result of the numerical simulation was validated through the experimental process, where a high degree of concordance in the mold filling time was achieved between both methods.

Enhancing GFRP fatigue durability for chassis component applications through glass fiber coupling variation

As the landscape of mobility trends continues to evolve, concerted efforts have been made to incorporate Carbon Fiber Reinforced Plastic (CFRP) into automotive components. However, the substantial increase in cost relative to the achieved weight reduction has limited its widespread adoption. Consequently, research endeavors have focused on exploring alternative composite materials, adapting fibers such as glass fibers, natural fibers, and recycled fibers, to reduce the cost of composite components. Of particular interest in the automotive industry is the utilization of Glass Fiber Reinforced Plastic (GFRP) in chassis components like leaf springs. Nevertheless, the development of GFRP leaf springs encounters a significant challenge related to the adhesive strength at the interface between epoxy resin and glass fibers, which is crucial for enhancing fatigue durability. While glass fibers were traditionally paired with unsaturated polyester or vinyl ester matrices, the pursuit of improved durability has led to the adoption of epoxy matrices. Regrettably, this transition has not consistently yielded the expected gains in interfacial adhesion.In light of these challenges, this study systematically compares the interfacial adhesion strength and fatigue endurance performance. For comparison, two coupling agents widely used commercially, amino silane and epoxy silane, were selected. Glass fibers treated with each coupling agent were purchased commercially, and glass fiber-reinforced plastic (GFRP) specimens were fabricated using the HP-RTM (High-Pressure Resin Transfer Molding) method. Static property evaluations and fatigue durability assessments were conducted using the fabricated specimens. The results showed that when epoxy silane was used as the coupling agent, the interlaminar shear strength (ILSS) increased by approximately 7 %. Furthermore, SEM(Scanning Electron Microscopes) analysis confirmed a significant enhancement in interfacial adhesion, providing support for the ILSS evaluation results. Consequently, the fatigue durability performance improved by approximately six-fold. This confirms that the improvement in interfacial adhesion due to the change in coupling agents led to enhanced fatigue durability performance.

High‐performance electromagnetic shielding composite materials based on carbon nanotubes and Sandwich laminate structures

AbstractCarbon fiber‐reinforced composite materials exhibit excellent mechanical and electromagnetic shielding capabilities. However, they have some drawbacks, such as high cost and significant reflection losses. In order to address these shortcomings, this study set out to design a sandwich‐structured composite material and produce a composite material designed for electromagnetic shielding using Vacuum Assisted Resin Transfer Molding (VARTM) technology. This composite material promotes the “absorption‐reflection‐reabsorption” process of electromagnetic waves, significantly enhancing its shielding effectiveness, achieving up to 59.4 dB of shielding effect in the 8.2–12.4 GHz (X‐band) range. The study also employed carbon nanotubes (CNTs) matrix doping to modify the composite material, significantly reducing reflection losses. When the amount of carbon nanotubes added reaches 0.6 wt%, the overall SE can be increased by 18%. Additionally, the introduction of CNTs significantly improves the flexural strength and tensile strength of the composite material; at a 0.6 wt% CNT content, the average tensile strength increased from 526.4 to 600.9 MPa, indicating good interfacial interactions between CNTs and epoxy resin. This work provides valuable insights for the preparation of high‐performance electromagnetic shielding materials, with profound theoretical and practical significance.Highlights Observations through SEM and CT scanning techniques reveal that Vacuum Assisted Resin Transfer Molding (VARTM) technology facilitates strong interlayer bonding between carbon fibers, glass fibers, and copper wires, alongside effective epoxy resin adhesion, thus enhancing the mechanical properties. The sandwich structure's impedance mismatch characteristic facilitates an efficient “absorption‐reflection‐reabsorption” process of electromagnetic waves. Additionally, the incorporation of Carbon Nanotubes (CNTs) enhances the absorption mechanism, reducing reflection losses. Incorporating CNTs further boosts both flexural and tensile strengths, attributed to improved interfacial interactions inhibiting crack formation.

An ultrasound-assisted resin transfer molding to improve the impregnation and dual-scale flow for carbon fiber reinforced resin composites

The imbalance of the dual-scale flow, i.e., microscopic intra-bundles and macroscopic inter-bundles flow, always generates voids in resin transfer molding (RTM) of composites, substantially weakening the mechanical performance. An ultrasound-assisted strategy to improve the impregnation and to balance dual-scale flow is promising to suppress the voids, while, it has still not been explored. Here, an ultrasound-assisted RTM for carbon fiber reinforced resin composites, realized by a self-developed device, is originally proposed. The influences of ultrasound vibration on the carbon fibers, resins, wettability, and impregnation process are systematically explored. Furthermore, the dual-scale flow, affected by the ultrasound vibration, is optimized. It is identified that the ultrasound vibration effectively reduces the viscosity of the resin and increases the roughness and surface activity of the fibers, hence significantly weakening the delayed impregnation in the intra-bundles, and speeding up the impregnation velocity in the inter-bundles. The reduction of the viscosity and the contact angle synergistically lowers the modified capillary number Ca*, hence balancing the dual-scale flow, while the excessively high impregnation velocity in the inter-bundles detrimentally enlarges Ca*, leading to the imbalance of the dual-scale flow. Accordingly, a critical ultrasound energy input (4 min of ultrasound vibration at the power range of 400–600 W) is figured out to achieve an optimal Ca*, providing a promising approach to suppress the flow-induced voids in composites manufacturing by RTM.