Resin Transfer Molding Process Research Articles

Influence of MoS2 nano-filler additions on wear behavior of carbon fiber reinforced epoxy composites

In this research work, two body wear and three-body wear performance of carbon fabric reinforced HTR 212 epoxy resin(CF/Epoxy) composites are experimentally evaluated. Carbon fabric/epoxy resin composite panels with MoS2 nano-filler additions of 0.1, 0.2, 0.4 and 0.7 weight percentage are developed by Vacuum Assisted Resin Transfer Molding process. Two Body Wear test is conducted on the prepared specimen in accordance with ASTM G-99, whereas Three Body Abrasive wear test is conducted as per ASTM G-65. Experimental Tests are conducted for sliding and abrading distances in multiples of 250 m up to 1500 m. Results reveal that Carbon fabric/epoxy resin composites with 0.7 weight percent of MoS2 show 18% reduction in two body wear compared to a decrease of 35% in Three Body abrasive wear at 1500 m abrading distance. Scanning Electron Microscopy is used to study the surface morphology of the tested samples and to know the mode of damage at the surface.

Near-infrared spectroscopy in resin transfer molding—determination of the degree of cure

AbstractNear-infrared (NIR) spectroscopy is employed to directly monitor the degree of cure of composite material during the curing phase in the resin transfer molding (RTM) process. The composite material consists of natural fibers and an epoxy-amine resin system. The quantitative determination of the degree of cure, α, from the NIR spectra is realized by partial least square (PLS) regression in conjunction with various pre-treatments of the spectral data. As a reference, the degree of cure is determined by isothermal differential scanning calorimetry (DSC) experiments. The best PLS model that could be obtained for α is characterized by a determination coefficient of prediction (R²P) of 0.980 and root mean square error of prediction (RMSEP) of 4.4 %. While the spectra change during curing according to the literature for each RTM trial, significant differences can be observed between the spectra of different RTM trials. The reasons for this are discussed in detail. The findings show the potential of inline NIR spectroscopy for monitoring α in the RTM process.

Dynamic wetting performance and resin-flow behavior of two-level selective laser-etched metal surface in resin transfer moulding process of fiber-metal laminates

ABSTRACT In selective laser etching for the interfacial strengthening of Fiber Metal Laminates (FMLs), the wettability of customized structured features significantly affects their overall mechanical properties. For two-level features, their complicated geometry makes the evaluation of wettability difficult, which introduces challenges to feature design. In this study, a sandwich FMLs comprising an AA2024-O metal skin and a plain-woven carbon-fiber fabric core is investigated. Three types of two-level feature interfaces are designed and introduced into the FMLs structure. To understand the effect of two-level features on the resin flow and dynamic wetting progress in resin transfer molding, two-phase flow Computational Fluid Dynamics numerical models coupled with porous media and level-set numerical methods are built. The feasibility of the numerical simulation in the qualitative analysis was verified by comparing the results with those of the testing porosity values from X-ray scanning. In addition, the mechanisms of pore formation and transportation are revealed. These results indicate that the deeper groove structure in the etched features plays an important role in discharging residual air and determining the transformation of pores to reduce porosity. The permeability orientations of the porous media and surface structure both have significant impacts on the flow behavior and formation of pores.

A Novel Preparation Method of Composite Bolted T-Joint with High Bending Performance Based on the Prepreg-RTM Co-Curing Process.

A co-curing resin system consisting of 9368 epoxy resin for prepreg and 6808 epoxy resin for resin transfer molding (RTM) was developed. A corresponding preparation method for a novel polymer composite bolted T-joint with internal skeleton and external skin was proposed based on the prepreg-RTM co-curing process, and novel T-joints were fabricated. A series of conventional configuration T-joints based on the RTM process and T-joints made of 2A12 aluminum alloy were prepared simultaneously. Bending performances were studied on these T-joints experimentally. The results indicate that 9368 epoxy resin and 6808 epoxy resin exhibit good compatibility in rheological and thermophysical properties. The novel T-joints prepared with the prepreg-RTM co-curing process show no obvious fiber local winding or resin-rich regions inside, and the interface quality between the internal skeleton and the external skin is excellent. The main failure modes of the novel T-joint under bending load include the separation of the skin and skeleton and the fracture along the thickness on the base panel; the skeleton carries the main bending load, but there is still load transfer between external skin and internal skeleton through their interface. The internal damages of the novel T-joint are highly consistent with surface damages observed visually, facilitating the detection and timely discovery of damages. The initial stiffness, damage initiation load, and ultimate load of the novel T-joint are 1.65 times, 5.89 times, and 3.45 times that of the conventional T-joint, respectively. When considering the influence of the density, the relative initial stiffness and relative ultimate load of the novel T-joint are 1.44 times and 2.07 times that of the aluminum alloy T-joint, respectively.

Environmental Impact of an Innovative Aeronautic Carbon Composite Manufactured via Heated Vacuum-Assisted Resin Transfer Molding

The Vacuum-Assisted Resin Transfer Molding (VARTM) process has gained popularity as a reliable and cost-effective alternative to autoclave molding for high-performance composite production, which is especially interesting for aeronautics, where weight reduction is crucial. However, to date, the environmental impact of components produced through VARTM remains relatively unknown. To address this gap, this study applied the Life Cycle Assessment (LCA) methodology to estimate the environmental impact of a thermoset composite laminate produced through heated VARTM. Aiming to support the decision, the VARTM composite part’s production was compared to conventional autoclave manufacturing, and the influence of alternative end-of-life (EoL) scenarios and energy mixes was considered, through LCA. The study found that energy consumption represented the majority of the environmental impacts of the heated VARTM component (33%), followed by carbon fibers, resins, consumables, and wastes. In terms of the comparative analysis, the autoclave manufacturing process showed better environmental results. Regarding EoL management, supercritical hydrolysis (with heat recovery) recycling emerges as the most beneficial method, reducing the impacts of the VARTM-manufactured component by 25%. This study emphasizes the importance of sustainable practices, such as reducing energy consumption, using low-carbon energy mixes, and adopting recycling methods to improve VARTM composite’s environmental performance.

Pultrusion vs RTM

Pultrusion and resin transfer molding (RTM) are two widely used manufacturing processes for producing composite materials. Kim Sjödahl, VP of technology and R&D at Exel Composites, considers the benefits of pultrusion and compares them to the RTM process.

Evaluation of resin impregnation using self-sensing of carbon fibers

The wettability of fiber-reinforced composites plays a crucial role in both mechanical properties and the efficiency of the manufacturing process. This is particularly significant in large and intricate composite structures where any flaws can have more severe consequences. In this study, the impregnation of epoxy resin into carbon fiber (CF) mats in-situ was monitored by observing the electrical resistance (ER) behaviors of CFs without any other additional sensors. The ERs of CF and CF tows at various points were measured, while epoxy resin was applied to establish fundamental data on ER behavior during the Vacuum Assisted Resin Transfer Molding (VARTM) process. During the VARTM process, the ERs of CF mats in-situ were compared with the behaviors of micro and sub-micro CFs, along with capturing images of the front flow of epoxy resin. The ER data obtained during the VARTM process was visualized through 3D ER mapping, which allowing for real-time monitoring of the flow front. Ultimately, the resin flow front of epoxy resin into CF mats was successfully monitored using the ER behaviors of CFs themselves.

Static and dynamic study of fiber-reinforced hemispherical stacked sandwich structure

Sandwich structures have garnered considerable attention due to their ability to meet the requirements of the aerospace and defense industry for impact resistance and lightweight performance. Unlike the plate or block construction investigated in previous studies, this present study proposes a new type of configuration known as the fiber-reinforced hemispherical stacked sandwich (FRHSS) structure. The fabrication of this FRHSS is achieved through the utilization of the Vacuum Assisted Resin Transfer Molding (VARTM) process and its response under quasi-static compression load is analyzed through both simulation and experiment. It is found that the internal configuration design effectively determines the direction of contraction in the hemispherical construction when it is subjected to quasi-static compression load. Furthermore, the impact resistance of the FRHSS against projectile penetration is also assessed. Through a comparison of simulation and experimental results, it becomes evident that the Chang-Chang failure criterion can successfully model the penetration process. Finally, the influence of internal configuration on the penetration resistance of the structure is studied by finite element method. The results show that the internal configuration plays an important role in the ballistic limiting velocity and ballistic performance of the construction. This study provides a valuable reference for the design of hemispherical sandwich structures.

Void formation and suppression in CFRP laminate using newly designed ultrasonic vibration assisted RTM technique

This study introduces an ultrasonic vibration assisted resin transfer molding (RTM) technique as an innovative approach to address the inherent challenges associated with traditional methods for producing CFRP laminates. It investigates the mechanism of void formation in CFRP composites under ultrasonic vibration using 3D X-ray microscopy. Numerical calculations and simulation analyses are also employed to validate the impact of ultrasonic vibration on mechanical properties of CFRP. The findings indicate that ultrasonic vibration results in CFRP laminates with more uniform thickness, leading to a substantial increase in fiber volume fraction up to ∼16 %. Concurrently, there are significant improvements in flexural strength (∼20 %) and fracture energy (∼90 %). Ultrasonic vibration also effectively reduces CFRP porosity by at least 25 %, resulting in a more consistent distribution of voids, primarily consisting of small circular voids. This porosity reduction is attributed to the cavitation effect and enhancing wettability, consequently improving the mechanical properties of CFRP. Moreover, simulations and numerical calculations demonstrate the significant occurrence of cavitation effect within the resin under specific process conditions. The intensity of cavitation is influenced by factors such as the initial bubble radius, acoustic pressure amplitude, and static pressure of the resin. The ultrasonic-assisted RTM process is proved as a promising method for producing CFRP laminates with superior properties.

Physical and mechanical characterization of glass fiber‐grewia optiva fiber reinforced hybrid polymer composite fabricated by vacuum assisted resin transfer moulding

AbstractThe natural and synthetic fibers are combined in a single composite to achieve a balance between the desired strength and cost considerations. In this study, the vacuum resin transfer moulding process was used to prepare an epoxy‐based composite. The composite consisted of grewia optiva as the natural fiber and glass fiber as the synthetic fiber, both with a fixed weightage of 10 %. Dolomite was used as a filler with varying content (0 %, 5 %, 10 %, and 15 weight %). The physical, mechanical, erosion wear and morphological behavior of the epoxy‐based composite were investigated. The inclusion of dolomite filler significantly increased the composite hardness and impact strength but reduced its tensile and flexural strength. At a dolomite filler content of 10 weight %, the erosive wear was reduced, while it increased at higher dolomite filler contents. The composite was examined using the L16 array, and the minimum wear rate was observed at an impingement angle of 30°, a velocity of 10 m/s, and an erodent size of 150 μm. Morphological studies were conducted to explore the possible mechanism for the variation in erosive wear at different dolomite contents in the hybrid composites.

Bayesian Optimal Experimental Design for Race Tracking in Resin Transfer Moulding

A Bayesian inference formulation is applied to the Resin Transfer Moulding process to estimate bulk permeability and race-tracking effects using measured values of pressure at discrete sensor locations throughout a preform. The algorithm quantifies uncertainty in both the permeability and race-tracking effects, which decreases when more sensors are used or the preform geometry is less complex. We show that this approach becomes less reliable with a smaller resin exit vent. Numerical experiments show that the formulation can accurately predict race-tracking effects with few measurements. A Bayesian A-optimality formulation is used to develop a method for producing optimal sensor locations that reduce the uncertainty in the permeability and race-tracking estimates the most. This method is applied to two numerical examples which show that optimal designs reduce uncertainty by up to an order of magnitude compared to a random design.

Modeling formation and evolution of voids in unsaturated dual scale preforms in Resin Transfer Molding processes

Modeling formation and evolution of voids in unsaturated dual scale preforms in Resin Transfer Molding processes

Effect of mold on curing deformation of resin transfer molding‐made textile composites

AbstractIn the process of preparing textile composites by resin transfer molding (RTM) method, both the upper and lower surface of the mold will interact with the composite parts due to the mismatch of thermal expansion coefficient between the mold and the part, resulting in warpage deformation. To address this key technical problem, this article first studied the effect of mold on the warpage deformation of composite material under different fiber volume fractions. Then a mold–part interaction modeling method for RTM process with nonthermoelastic deformation is proposed. By introducing shear layers between the upper and lower surfaces of the mold and the composite part, a finite element simulation model for predicting the curing deformation of the component is established and experimentally verified. The results show that the effect of mold–part interaction on the warpage deformation of the composite decreases with increasing fiber volume fraction. Meanwhile, the proposed modeling method can avoid complete material characterization, and the comparison between experimental and simulation results proves that the model can accurately simulate the curing deformation of composite components under the same process conditions. Finally, the analysis reveals that the interaction caused by thermal mismatch between the composites and the mold is less related to the intermediate layup, but mainly related to the fiber orientation of the layup layer in contact with the mold.Highlights The warpage deformation law of the mold on the composites with different fiber volume fractions is investigated. A mold–part interaction modeling method for a resin transfer molding process with nonthermoelastic deformation is proposed, where the mold stretching effect is represented by the cumulative effect of the interaction between the two layers on the upper and lower surfaces of the part.

Strength Assessment of PET Composite Prosthetic Sockets.

A prosthesis is loaded by forces and torques exerted by its wearer, the amputee, and should withstand instances of peak loads without failure. Traditionally, strong prosthetic sockets were made using a composite with a variety of reinforcing fibres, such as glass, carbon, and Kevlar. Amputees in less-resourced nations can lack access to composite prosthetic sockets due to their unavailability or prohibitive cost. Therefore, this study investigates the feasibility of polyethylene terephthalate (PET) fibre-reinforced composites as a low-cost sustainable composite for producing functional lower-limb prosthetic sockets. Two types of these composites were manufactured using woven and knitted fabric with a vacuum-assisted resin transfer moulding (VARTM) process. For direct comparison purposes, traditional prosthetic-socket materials were also manufactured from laminated composite (glass-fibre-reinforced (GFRP)), monolithic thermoplastic (polypropylene (PP) and high-density polyethylene (HDPE)) were also manufactured. Dog-bone-shaped specimens were cut from flat laminates and monolithic thermoplastic to evaluate their mechanical properties following ASTM standards. The mechanical properties of PET-woven and PET-knitted composites were found to have demonstrated to be considerably superior to those of traditional socket materials, such as PP and HDPE. All the materials were also tested in the socket form using a bespoke test rig reproducing forefoot loading according to the ISO standard 10328. The static structural test of sockets revealed that all met the target load-bearing capacity of 125 kg. Like GFRP, the PETW and PETK sockets demonstrated higher deformation and stiffness resistance than their monolithic counterparts made from PP and HDPE. As a result, it was concluded that the PET-based composite could replace monolithic socket materials in producing durable and affordable prostheses.

Method of Manufacturing Structural, Optically Transparent Glass Fiber-Reinforced Polymers (tGFRP) Using Infusion Techniques with Epoxy Resin Systems and E-Glass Fabrics.

Recently, fiber-reinforced, epoxy-based, optically transparent composites were successfully produced using resin transfer molding (RTM) techniques. Generally, the production of structural, optically transparent composites is challenging since it requires the combination of a very smooth mold surface with a sufficient control of resin flow that leads to no visible voids. Furthermore, it requires a minimum deviation of the refractive indices (RIs) of the matrix polymer and the reinforcement fibers. Here, a new mold design is described and three plates of optically transparent glass fiber-reinforced polymers (tGFRP) with reproducible properties as well as high fiber volume fractions were produced using the RTM process and in situ polymerization of an epoxy resin system enclosing E-glass fiber textiles. Their mechanical (flexural), microstructural (fiber volume fraction, surface roughness, etc.), thermal (DSC, TGA, etc.), and optical (dispersion curves of glass fibers and polymer as well as transmission over visible spectra curves of the tGFRP at varying tempering states) properties were evaluated. The research showed improved surface quality and good transmission data for samples manufactured by a new Optical-RTM setup compared to a standard RTM mold. The maximum transmission was reported to be ≈74%. In addition, no detectable voids were found in these samples. Furthermore, a flexural modulus of 23.49 ± 0.64 GPa was achieved for the Optical-RTM samples having a fiber volume fraction of ≈42%.

Predicting the effect of voids generated during RTM on the low-velocity impact behaviour by machine learning-based surrogate models

The main objective of the present paper is to demonstrate the feasibility of machine-learning-based surrogate models for predicting low-velocity impact behaviour considering void content and location generated during the resin transfer moulding process. Generating reliable experimental datasets for training those models is almost impossible, therefore an adapted finite element model was implemented providing reliable results to generate the synthetic datasets. The optimum hyperparameter combination for training the Random Forest model was found based on the grid search technique. The accuracy of the classification, single-output regression and multi-output regression models was sufficient. It was concluded that the multi-output regression model, which predicts the force-time, displacement-time, and energy-time curves, provides the best information, and is sufficiently accurate (R2 > 0.995) and fast (5 s per sample) as an online structural performance monitoring tool.

Preparation and properties of carbon fiber reinforced bio‐based degradable acetal‐linkage‐containing epoxy resin composites by RTM process

AbstractThe recycling of carbon fiber (CF) reinforced bio‐based degradable epoxy resin composites is of great significance for resource saving, environment protection and sustainable development of economy and society. Resin transfer molding (RTM) has been recognized as one of the most promising processes to manufacture CF Reinforced polymeric composites cost‐effectively. The bio‐based diglycidyl ether pentaerythritol vanillin diacetal (DEPVD) epoxy resin used in this study is an epoxy resin that can be degradable under mild conditions. And its CF composites were prepared by the RTM process using DDS as a curing agent and low viscosity bisphenol A‐E51 epoxy resin as a diluent. The chemical rheological properties, curing behavior, thermal stability, dynamic viscoelasticity and mechanical properties of DDS‐E51‐DDS epoxy resin were investigated. It is found that the increase of DEPVD content is beneficial to improve the mechanical properties, Tg and solid residue after thermal degradation of DEPVD‐E51‐DDS epoxy resin. Moreover, the effects of DEPVD content in epoxy resin on the mechanical properties of CF/DEPVD‐E51‐DDS composites were evaluated. When the DEPVD content is 70%, the tensile and flexural strength of CF/EPVD‐E51‐DDS composites are 1649.4 MPa and 1207.4 MPa, respectively. The degradability and mechanism of CF/DEPVD‐E51‐DDS composites were further investigated. CF/DEPVD‐E51‐DDS composites containing 70% DEPVD have excellent degradability, and the recycled CFs exhibit comparable mechanical properties to the virgin CFs, which demonstrates a novel way to recover the high‐quality of used CFs.

Mechanical, Thermal Properties and Void Characteristics of Bamboo Fiber-Reinforced Epoxy Resin Composites Prepared by Vacuum-Assisted Resin Transfer Molding Process

ABSTRACT This study aimed to examine the effect of epoxy resin (EP) systems on the impregnation of bamboo fibers (BFs) by EP and the properties of BF/EP composites prepared by vacuum-assisted resin transfer molding (VARTM) process. BF preforms obtained by solution suspension method were used as reinforcement, and epoxy/anhydride system (EP-1), epoxy/amine system (EP-2) and two-component epoxy system (EP-3) were employed as matrix; on this basis, BF/EP-1, BF/EP-2 and BF/EP-3 composites were prepared by VARTM. The physical, mechanical and thermal properties and void characteristics of BF/EP composites were characterized. The results showed that EP-1 with a viscosity of 265 mPa·s at 23°C and an operating time of room temperature without curing was beneficial for the EP-1 to impregnate BFs adequately and uniformly. The incorporation of BFs into EP-1 significantly improved the flexural, shear and impact properties, thermal properties and interface properties of EP-1. Moreover, the properties of BF/EP-1 composites were better than those of BF/EP-2 and BF/EP-3 composites. Three-dimensional X-ray microscopy scans revealed that the volume and distribution of voids in the BF/EP composites differed significantly depending on the EP systems, and the percentage of void volume in the BF/EP-1 composites was only 0.14% in 3D reconstruction models.

Performance analysis of hybrid bio-composites developed through different processing routes for automobile application

The performance of polymer composites strongly depends upon the constituents and the processing method of composite fabrication. The present study investigates the effect of fabrication processes (hand lay-up process, compression molding and resin transfer molding (RTM)) on the physical and mechanical properties of the developed bio-composites having different combinations of uni-directional sisal and uni-directional ramie fiber mat reinforcement in unsaturated polyester matrix. Scanning electron micrographs (SEM) were used to study the failure behavior of composite constituents under various loading conditions. Results indicate that composites fabricated by RTM process showed 5%–15% voids (percentage density change) while hand lay-up showed 30%–45% voids (percentage density change). Longitudinal and transverse flexural modulus of composites fabricated by RTM and compression molding are 2–3 times higher than composites developed by hand lay-up process. The study concludes that processing of composites through different routes and varying the reinforcement have significant effect on mechanical properties of the developed bio-composites.

Efficient dual-scale flow simulation for Resin Transfer Molding process based on domains skeletonization

In the Resin Transfer Molding (RTM) process, a polymeric resin is injected inside a dry preform to fill the gaps around and inside the fiber tows. Simulating this process at the scale of the tows is challenging because of the computational cost associated to solving a three-dimensional dual-scale flow problem. In this work, a novel Dual-Scale Skeleton model (DSS) is introduced, capable of solving a dual-scale flow problem at an affordable computational cost. The three-dimensional geometry of a multi-layer layup, consisting of inter-tow channels and permeable tows, is replaced by a skeletonized representation of the original subdomains. Dual-scale flow is modeled using a Reynolds-Darcy finite elements formulation. The model is validated numerically and its application is demonstrated over a few test cases. The adoption of the DSS model allows one to simulate complex dual-scale flow problems over large domains at a reduced computational cost when compared to full 3D solutions.