Vacuum Assisted Resin Infusion Process Research Articles

Effects of crosslinker concentration on curing process and performances of needled fiber preform reinforced phenolic aerogel composite using process simulation and comprehensive experiments

A kind of needled quartz/carbon fiber preform reinforced phenolic aerogel composite (NQCF/PR) was fabricated through impregnating needled fiber preform with phenolic resin precursor solution, followed by sol–gel polymerization and solvent drying. The needled fiber preform serves as lightweight quasi-three-dimensional reinforcement, while phenolic aerogel matrix provides high porosity and low thermal conductivity. During fabrication of aerogel composite part using vacuum-assisted resin infusion process, distribution of crosslinker hexamethylenetetramine (HMTA) in precursor solution can be problematic, as precipitated crosslinker particles may be filtered by fibrous preform. In this study, the impact of HMTA filtration induced heterogeneous structure on subsequent curing process was investigated using process simulation. Temperature effects of sol–gel polymerization and solvent evaporation were considered through establishment of corresponding kinetic models. Impacts of heterogenous structure on distribution of temperature, resin curing degree and solvent conversion degree in large hemispherical aerogel composite structure were investigated. This leads to variations in gel network and pore structure of aerogel, thereby affecting final material performance. Based on experimental results, as HMTA concentration increases, compressive performance of NQCF/PR obviously increases. Among these, NQCF/PR with 4.7 wt% HMTA provides a balance of lightweight nature (0.25 g/cm3), excellent thermal insulation property (0.052 W·m−1·K−1) and compressive performance (strength of 0.35 MPa).

Flexural and interlaminar shear response of novel methylmethacrylate composites reinforced with high-performance fibres

This experimental work presents a comparative study on the mechanical behaviour of novel infusible methylmethacrylate matrix (Elium®) composites reinforced with different types of high-performance fibres. A vacuum-assisted resin infusion process was employed to fabricate the laminates using carbon, basalt, Kevlar®, and high molecular weight polyethene (UHMWPE) fibres. Flexural and interlaminar shear properties of the composites were evaluated. Test results revealed that carbon fibre composites had superior flexural strength, stiffness and interlaminar shear stress as compared to the other composites tested. Further, composites containing Kevlar and UHMWPE fibres demonstrated significantly higher flexural strains to failure. Post-testing, specimens were examined using scanning electron microscopy (SEM). Microscopy revealed possible interfacial interaction differences based on the reinforcement fibre type, which was further confirmed by an analytical approach for analysing the flexural behaviour of various types of composites. The sequence of damage progression in specimens was also analysed.

Effect of halloysite addition on the dynamic mechanical and tribological properties of carbon and glass fiber reinforced hybrid composites

Composite materials have become prominent in the aerospace, automotive, wind energy, biomedical, and machine tool industries. This has demanded the evaluation of the dynamic mechanical and tribological behaviour of composites to understand their performance and ensure their reliability and safety in varied operating conditions. In this study, the effect of halloysite nano-clay addition on the dynamic mechanical and tribological properties of the carbon/glass hybrid composites was investigated. The composites were produced with the vacuum assisted resin infusion process. by varying the content of halloysite nano-clay (1, 3, and 5 wt%). The dynamic mechanical properties of the manufactured composites were examined at temperatures ranging from 30 °C to 180 °C. The tribological properties of the specimens were assessed by varying the applied load (10, 20, and 30 N), sliding speed (1.5, 3, and 4.5 m/s) and sliding distance (500, 1000, and 1500 m). Box-Behnken design was utilized to optimize the number of experiments. The results showed that the halloysite-added samples had better dynamic mechanical and tribological properties than the carbon/glass hybrid composites. Especially, hybrid composites containing 3 wt% halloysite outperformed the other composites investigated. A scanning electron microscope (SEM) was used to examine the worn surface and wreckage in the investigated composite specimens.

Mechanical and viscoelastic properties of novel resin-infused thermoplastic tri-block copolymer 3D glass fabric composites

The current study investigates the mechanical and viscoelastic properties of a novel acrylic resin-infused thermoplastic (Elium®) tri-block copolymer (Nanostrength®) 3D fibre-reinforced composites (FRCs). The toughened thermoplastic resins with three different concentrations of tri-block copolymer, i.e., 10 wt%, 15 wt%, and 20 wt%, were prepared and used to fabricate thermoplastic 3D-FRCs using a vacuum-assisted resin-infusion process at room temperature. The flexural, interlaminar, and viscoelastic properties and failure modes were evaluated and compared with those of pristine thermoplastic 3D-FRCs. The addition of tri-block copolymer significantly improves the flexural strength of 3D-FRC (up to 75 % and 34 % along the warp and fill directions, respectively, at 15 wt% of tri-block copolymer) and interlaminar shear strength (up to 80 % and 111 % along the warp and fill directions, respectively, at 20 wt% of tri-block copolymer). Additionally, the residual flexure and interlaminar shear strength improved up to 35 % and 109 % at 15 wt% of tri-block copolymer. Dynamic mechanical analysis (DMA) demonstrated that the glass transition temperature and storage modulus of thermoplastic 3D-FRCs were increased up to 11 °C and 24 %, respectively at 20 wt% of tri-block copolymer, which may be due to increased physical crosslinking and the agglomeration of tri-block copolymer particles. The improved mechanical and viscoelastic properties of resin-infused thermoplastic tri-block copolymer 3D-FRCs are attributed to better interface adhesion, improved matrix toughness, and crack-bridging mechanisms induced by the tri-block copolymer. The toughened thermoplastic 3D-FRCs can be utilized in the design and development of composite structures for improved damage tolerance applications.

Lateral compressive behavior of multi-layer lattice-web reinforced composite cylinders

Several novel multi-layer lattice-web reinforced composite cylinders, consisting of glass fiber reinforced polymer (GFRP) face sheets and lattice webs, polyurethane (PU) foam core and clay ceramsite filler, were proposed and manufactured using a vacuum assisted resin infusion process (VARIP) method. A series of quasi-static lateral compressive experiments were carried out to investigate the feasibility of the proposed cylinders. For both the hollow composite cylinders and ceramsite filling composite cylinders, the bearing capacity and energy absorption performance can be significantly improved with the use of multi-layer lattice-web layouts. Among the proposed three types of lattice-web layouts, the double-layer dislocated lattice-web layout made the composite cylinder exhibit the greatest specific energy absorption (SEA) performance and can be chosen as an optimal configuration. Furthermore, numerical models were established using LS-‍DYNA software to simulate the large deformation of the composite cylinders with double-layer dislocated lattice-web layout. Based on the numerical models, parametric analysis was carried out to discuss the effects of various parameters on the crushing response of the composite cylinders. Generally, using thicker GFRP material or higher radial lattice web can make the composite cylinders present an increased likelihood of brittle failure. However, filling ceramsite can not only make them exhibit plastic deformation characteristics but also facilitate the full utilization of various components.

Effect of seawater aging on the erosive wear response of aramid fiber reinforced composites

This study presents the effect caused by the saline environment (artificial seawater) on the physical and tribological properties of laminated composite materials reinforced with aramid fibers when they are subjected to erosive wear by sand particles. Composite materials made by epoxy resin and reinforced with glass fiber, carbon fiber and hybrid fiber (aramid with carbon) were studied. The laminates were superficially reinforced with layers of Kevlar fiber and prepared by the vacuum-assisted resin infusion process. The samples were subjected to a seawater accelerated aging process at 70°C for 1122 h. To reproduce erosive wear conditions of marine structural components, sea sand was used as solid particle under conditions of 4.5 bar of pressure, impact speed of 4.7 m/s and impact angle of 90°. The results showed that aged materials absorb more impact energy with respect to unaged counterparts, causing less material loss and a less depth in the wear track. The information generated by this research work may serve for the design and durability analysis of marine structures such as tidal turbine blades.

An experimental study on the failure mechanism of local-strengthening glass fiber reinforced polymer T-joints under/after the low-velocity impact loading

In this study, an experimental methodology, consisting of low-velocity impact (LVI) and quasi-static compressive test, is conducted to investigate the performance and failure mechanism of GFRP T-joints, fabricated by vacuum-assisted resin infusion process (VARI), when subjected to out-of-plane LVI loading at the corner. Further, the effect of LVI loading on the reduction of strength is analyzed by the tensile test after LVI. In order to improve the strength of the GFRP T-joints, one layer of stainless-steel wire net (SSWN) is inserted into the corner of the T-joints structure. The experimental results indicate that the addition of SSWN decreases the damaged area of delamination in the web, meanwhile, connecting the nearby GFRP layers to avoid the structure failure suddenly, which improves its performance of tensile test after LVI.

Crushing behavior of multi-layer lattice-web reinforced double-braced composite cylinders under lateral compression and impact loading

This paper reports on the crushing behavior of several novel multi-layer lattice-web reinforced double-braced composite cylinders composed of glass fiber reinforced polymer (GFRP) face sheets, GFRP lattice webs, polyurethane (PU) foam core and steel bars. A series of quasi-static lateral compression and low-velocity impact experiments were carried out to investigate the feasibility of the proposed cylinders. All the experimental specimens were manufactured using a vacuum assisted resin infusion process (VARIP) method. The bearing capacity and energy absorption performance of the composite cylinders can be significantly improved with the enhancement of multi-layer lattice-web layout and use of bracing. Among the proposed three types of lattice-web layouts, the double-layer dislocated lattice-web layout made the composite cylinder exhibit the greatest specific energy absorption (SEA) performance and good impact resistance property and can be chosen as an optimal configuration. Furthermore, numerical models were established using LS-DYNA software to simulate the large deformation of the composite cylinders with double-layer dislocated lattice-web layout. Based on the numerical models, parametric analysis was carried out to discuss the effects of various parameters on the crushing behavior of the composite cylinders. The bearing capacity and impact resistance property can be generally improved with the increase of GFRP thickness or radial lattice-web height. Additionally, using stronger foam material or smaller inclination of bracing can increase the absorbed energy in PU foam but the GFRP material always makes an essential contribution to the energy absorption of the composite cylinders.

Influence of stacking sequence and halloysite addition on the fracture toughness and low‐velocity impact strength of carbon/glass fiber reinforced hybrid composites

AbstractThe objective of this study is to produce bidirectional woven carbon/glass fiber reinforced epoxy hybrid composites and to assess their fracture toughness (FT) and low‐velocity impact strength. The composites were produced for the study by changing the stacking order of fiber layers using a vacuum assisted resin infusion process. In addition, the consequence of halloysite nano‐clay addition on the above properties were explored. The outcomes disclosed that the arrangement of fiber layer notably influences the FT and low‐velocity impact strength of the composites. Particularly, the addition of more carbon fiber layers played a key role in enhancing the FT of hybrid composites, while a reverse trend was observed for low‐velocity impact strength of composites due to the elastic nature of glass fibers, which absorbs more energy through global deformation. Additionally, the incorporation of halloysites enhanced the FT and impact strength of hybrid composites due to increased interfacial adhesion between composite elements. In addition, morphological analysis was conducted to evaluate the damage morphologies and failure mechanisms of tested laminates, which offers crucial information for the structural design of these laminates as well as for the enhancement of their performance.Highlights Fracture toughness and impact strength of hybrid composites were investigated. Arranging carbon fibers on the extreme layers enhanced the fracture toughness. Glass fiber used in hybrid composite supports to increase their impact strength. Addition of halloysite improved the overall performance of hybrid composites.

In-situ monitoring of carbon fiber-reinforced plastic manufacturing using electrical resistance during infusion

Carbon fiber reinforced plastics (CFRPs) have been widely applied in various fields such as aerospace, vehicles, and civil infrastructure, even though their manufacturing time, labor, and cost are burdensome compared to other materials. However, studies on monitoring systems for composite manufacturing are limited. The spotlight is biased toward CFRP design and functional nanocomposites. Therefore, in this study, an in-situ monitoring system of a CFRP is proposed to investigate the vacuum-assisted resin infusion process in real time using electrical resistance changes. Specifically, two electrode types namely Cu tape and silver paste, were comparatively analyzed under several vacuum bag pressures. Resin impregnation was then investigated on the scale of a carbon fiber single tow and laminae. Impregnated resin increases the thickness of the laminae, thereby increasing the electrical resistance. Moreover, the curing behavior of the resin was correlated with changes in its electrical resistance so that the viscosity and degree of curing of the resin could be identified. The proposed method enables the detection of not only the resin front, but also the degree of curing.

Synergistic effect of r-GO on the mechanical, microstructural and high velocity impact behaviour of synthetic fibre reinforced NiTi intermetallic laminates

In this work, the effect of different concentration (0.5, 1 and 1.5 wt%) of reduced graphene oxide (r-GO) on the mechanical, microstructural and high velocity impact behaviours of novel fibre intermetallic laminates (FIL) made up of Nitinol foils and carbon/aramid fibres were experimentally investigated. The vacuum assisted resin infusion process is employed to fabricate the FILs with alternatively stacked woven fibres. The mechanical and chemical surface treatments were performed to ensure the improved adhesion and interaction between epoxy matrix and nitinol foils. The mechanical properties such as tensile, flexural and high velocity impact strengths were investigated for unreinforced, and r-GO reinforced FILs. Results revealed that the assimilation of r-GO fillers exhibit the capable of improving ultimate tensile strength of 16.5%, ultimate flexural strength of 13.9% and impact strength of 7.62% compared to unreinforced FILs. Improved tensile, flexural and impact strengths were obtained at the concentration of 1wt% r-GO infused FILs. On the contrary, the mechanical properties are deteriorated with further addition of r-GO fillers above the optimum levels. Moreover, the morphologies of surface treated Nitinol foils, nano filled epoxy matrix and the mechanical fractured surfaces were investigated with the aid of SEM to assimilate the failure mechanisms with respect to the inclusion of reduced-graphene oxide.

Mechanical performances of polyvinyl chloride (PVC) foam sandwich composites with glass cloth face-sheet

The mechanical performances of polyvinyl chloride (PVC) foam sandwich panels with different types of cores prepared by vacuum-assisted resin infusion process (VARI) were investigated. The flatwise, edge-wise compression, flexural and impact properties of three types of PVC sandwich panels of the prepared panels were performed. The results show that the mechanical performances of the foam sandwich composites can be enhanced due to the presence of polymer pins, and the impact properties appear slightly different at different stages. Due to the existence of pins, the energy absorption and impact properties of the sandwich panels are slightly reduced during the impact rebound phase, while the impact properties of the three sandwich panels do not change much during the impact penetrated phase. The contact surface and the cross-section through the damaged area were observed to analyze the failure modes of sandwich composites.

Optimization of Characteristics Polymer Composite Reinforced Kenaf and Jute Fiber Using Taguchi-Response Surface Methodology Approach

ABSTRACT The use of composite materials with natural fiber reinforcement (CMNFR) has experienced rapid development in the automotive industry to apply synthetic materials that are expensive and not environmentally friendly. Biocomposite is a composite consisting of a polymer matrix and natural fiber reinforcement. Natural fiber materials are used as a substitute for conventional non-renewable reinforcing materials. This study uses the vacuum-assisted resin infusion (VARI) process to fabricate composites using woven kenaf and jute from natural fiber. The Taguchi experimental design method with L27 3 as an orthogonal array matrix was used in this research to obtain the optimum CMNFR fabrication parameters. Response Surface Methodology is used to obtain the optimal response value based on microstructural analysis. The factors used were NaOH treatment (4, 6, 8 wt%), water absorption test (6, 12, 24 hours), and fiber type (KF, JF, KF-JF). The study’s results found a combination of optimization of CMNFR manufacturing parameters using RSM, namely, A1B1C2 with a mean material strength of 0.241 J/mm2 (impact strength) and a combination of A1B3C1 parameters with a mean material strength of 94.8650 MPa (flexural strength). It was also found that the presence of contaminants and voids harmed the mechanical properties.

Durability Study of Glass/Carbon Hybrid Composites Immersed in Seawater for Marine Application

The hybridization of carbon fiber (CFRP) and glass fiber (GFRP) composites is required to overcome the disadvantages of GFRP composites and their commercial feasibility for marine applications. This study was conducted on a hybrid glass/carbon composite with a vinyl ester matrix made by vacuum-assisted resin infusion process with a stacking sequence of [GCG2CG2C] s. Composites are immersed in natural seawater for up to 6 months. The maximum weight gain of e-glass/carbon hybrid composite is 0.79%. The results showed that the tensile, shear and compressive strengths of the glass/carbon hybrid composite after immersion in natural seawater decreased to 19%, 13%, and 50%, respectively. The decrease in compressive strength is the highest compared to others. It indicates that compressive strength should be of more significant concern for marine environmental applications. SEM analysis exhibited that seawater absorption causes the matrix, fiber, and fiber/matrix interface degradation. It is indicated by the absence of a firm matrix fracture surface, the number of fractures in the thread, the presence of fiber/matrix debonding, and fiber pull-out in the specimen after immersion in seawater. It is the cause of the decrease in the mechanical properties of the hybrid composite.

Resorcinol-Derived Vitrimers and Their Flax Fiber-Reinforced Composites Based on Fast Siloxane Exchange.

Natural fiber-reinforced composites are gaining increased interest for their significantly reduced carbon footprint compared to conventional glass or carbon fiber-based counterparts. In this study, natural fibers are used in a resorcinol-based epoxy resin that is thermally reshapable at higher temperatures (>180°C) by using fast exchanging siloxane bonds, catalyzed by 1,5,7-triazabicyclo[4.4.0]dec-5-ene. Stress relaxation times of only about 6s at 220°C can be reached. A resorcinol-based epoxy compound is selected because it can be derived from cellulose, opening ways for more sustainable and reshapable composite materials. In a last step of the research, the low viscosity vitrimer formulation (<200mPas) is applied to make a flax fiber-reinforced composite using an industrially relevant vacuum-assisted resin infusion process. A section of this composite is successfully reshaped, which allows for envisioning a second life for natural fiber-reinforced composites.

Effect of Flame Treatment on Bonding Performance of GF/EP Pultrusion Sheets Used for VARI Process

This paper presents an easy and low-cost flame treatment method to improve the bonding performance of GF/EP (Glass Fiber-Reinforced Epoxy) pultrusion plates, which are using widely for large size wind blades. In order to explore the effect of flame treatment on the bonding performance of the precast GF/EP pultruded sheet vs. the infusion plate, the GF/EP pultruded sheets were treated with different flame treatment cycles and were embedded in the fiber fabrics during the vacuum-assisted resin infusion process (VARI). The bonding shear strengths were measured by tensile shear tests. It is found that after 1, 3, 5, and 7 flame treatments, the tensile shear strength between the GF/EP pultrusion plate and infusion plate increased by 8.0%, 13.3%, 22.44%, and -2.1%, respectively. This indicates that the maximum tensile shear strength can be obtained after five times of flame treatment. In addition, DCB and ENF tests were also adopted to characterize the fracture toughness of the bonding interface with the optimal flame treatment. It is found that the optimal treatment gives increments of 21.84% and 78.36% for G I C and G II C, respectively. Finally, the surficial topography of the flame-treated GF/EP pultruded sheets were characterized by optical microscopy, SEM, contact angle test, FTIR, and XPS. The results show that flame treatment plays an impact on the interfacial performance through the combination of physical meshing locking and chemical bonding mechanism. Proper flame treatment would remove the weak boundary layer and mold release agent on the surface of the GF/EP pultruded sheet, etch the bonding surface and improve the oxygen-containing polar groups, such as C-O and O-C=O, to improve the surface roughness and surface tension coefficient of pultruded sheet to enhance the bonding performance. Excessive flame treatment destroys the integrity of epoxy matrix on bonding surface which results into the exposure of the glass fiber, and the carbonization of release agent and resin on the surface loosen the surficial structure, which reduces the bonding properties.

Experimental investigation on the compression-after-double-impact behaviors of GF/epoxy laminates embedded with/without metal wire nets

This work investigated the effect of embedded metal wire nets on both double-point low-velocity impact (LVI) and compression-after-double-impact (CAI) behaviors of glass fiber-reinforced polymer (GFRP) laminates. The once-forming conventional GFRP laminates with metal wire nets are manufactured by the vacuum-assisted resin infusion (VARI) process. A novel fixture is designed to conduct the double-point LVI experiment with a different impact distance. The results, including impact response history and failure morphology, demonstrate that adding wire nets can improve the impact-resistance capacity of GFRP by dispersing the incident energy from the impact center to the outer region. Under the impact distance of 20 mm and impact energy of 60 J, the energy absorption rate of the wire net-hybrid laminates is 19.18% lower than that of the pure GFRP laminates. According to the scanning electron microscope (SEM), the damage on hybrid laminates is concentrated near the metal mesh, leading to a more extensive damage area. In the CAI tests, the performance of hybrid laminates is poorer than that of conventional GFRP under the condition of both high incident energy and distance.

An experimental study on the failure and enhancement mechanism of bolt-strengthening GFRP T-joint subjected to tensile loading

Abstract The aim of this article is to investigate the failure and enhancement mechanism of bolt-strengthening glass fiber-reinforced polymer (GFRP) T-joints under quasi-static tension. One-step molding technology based on the vacuum-assisted resin infusion process is carried out to fabricate the GFRP T-joints structures. Then, a special fixture and constraint condition are set up to take the quasi-static tensile test with high reliability. Moreover, it is demonstrated that the T-joints structures may decrease their bearing capacity, resulting in interlaminar delamination at the corner region. Further, to strengthen the T-joints, the bolts are employed to effectively prevent the initiation and propagation of interlaminar delamination in the tensile loading. At the same time, as their enhancement and failure mechanisms are revealed deeply, the strengthening method is optimized as well.

Static and dynamic mechanical properties of carbon fiber reinforced polymer with different stacking sequences

With the wide application of carbon fiber reinforced polymer (CFRP) composites, dynamic loading cases are increasingly considered in structural design and analysis. Hence, it is necessary to investigate their dynamic mechanical properties. In this paper, the carbon/epoxy laminates with different stacking sequences prepared by vacuum assisted resin infusion process were studied by quasi-static tension and split Hopkinson tension bar experiments. The loading strain rate is ranged from 2.2 × 10−4 s−1 to 2200 s−1. The results indicate that the composites are strain rate dependent. Four stacking sequence laminates show different strain rate sensitivities, and their mechanical performance differences depend on the strain rate. As the strain rate increases, tensile strength and elastic modulus increase, but failure strain decreases. Therein, the elastic modulus is highly sensitive. The elastic modulus difference of unidirection/cross-ply or unidirection/quasi-isotropic decreases but that of unidirection/angle-ply increases with increasing strain rate. The failure strain difference of unidirection/angle-ply decreases significantly with increasing strain rate. These experimental data and research results could provide some insight for epoxy matrix CFRPs.

Experimental and Numerical Investigations of the Vibration and Acoustic Properties of Corrugated Sandwich Composite Panels

To explore the lightweight structures with excellent vibration and acoustic properties, corrugated composite panels with different fiber reinforcements, i.e., carbon and glass fibers, were designed and fabricated using a modified vacuum-assisted resin infusion (VARI) process. The vibration and sound transmission loss (STL) of the corrugated composite panels were investigated via mode and sound insulation tests, respectively. Meanwhile, finite element models were proposed for the verification and in-depth parametric studies. For the vibration properties of the corrugated composite panels, the results indicated that the resin layer on the panel surface, despite the extremely low thickness, showed a significant effect on the low-order bend modes of the entire structure. In addition, the difference in the mode frequency between the panels consisting of different fiber types became more and more apparent with the increase of the frequency levels. For the sound insulation property of the panel, the initial frequency of the panel’s resonant sound transmission can be conveniently increased by increasing the layer thickness of surface resin, and the fraction of fiber reinforcements is the most predominant factor for the sound insulation property, which was significantly improved by increasing the thickness of the fiber cloth. This work can provide fundamental support for the comprehensive design of vibration and acoustics of the composite sandwiched panel.