Vacuum Assisted Resin Infusion Research Articles

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.

Damage progression monitoring using self-sensing capability and acoustic emission on glass fiber / epoxy composites and damage classification through principal component analysis

In this study, the synergistic combination of acoustic emission (AE) and self-sensing capability provided by the integration of carbon nanotube (CNT) networks was used to a better damage progression monitoring of glass fiber epoxy composites under flexural loading. The specimens were prepared with different stacking sequences ([06], [04], [0/90]S, and [90/0]S) using the vacuum assisted resin infusion procedure. The acoustic signals recorded during the tests were analyzed by a classification methodology which consists of the k-means method and principal component analysis (PCA), this analysis allowed the identification of the various damage mechanisms such as matrix cracking, fiber/matrix debonding, delamination and fiber breakage. The electromechanical response, through the change in electrical resistance signal, and some AE parameters such as the cumulative energy and/or strength cumulative were able to capture the occurrence of specific failure events during the composites damage evolution. Damage evaluation of failed specimens by means of scanning electron microscopy was performed, and it exhibited a less damage severity on specimens with CNT due to the reinforcement effect. This work demonstrates the complementarity of both non-destructive inspection techniques for monitoring damage progression in composite structures.

Low velocity impact behavior of twill basalt/epoxy composites modified by graphene nanoparticles

Nanoparticles are considered as feasible strengthening agent which strengthen different types of polymeric materials with minor reduction in the density of composites. In this study, 0.1 and 0.5 wt. % Graphene Nano Platelets (GNPs) are added to the matrix of basalt fiber reinforced epoxy composites (BECs) and the effects of such addition on low velocity impact behavior are investigated. In this regard, the epoxy matrix is reinforced in macro scale by basalt fibers weaved together in 2/2 Twill pattern. Vacuum Assisted Resin Infusion Molding (VARIM) method is used to fabricate the pure and multi-scale BECs. The profile energy method is also used to evaluate the penetration and perforation threshold of fabricated pure and multi-scale BEC specimens. The force versus time and deflection, energy and deflection versus time curves are plotted and the key parameters of low velocity impact test including maximum force, energy and deflection are compared. According to the results, introducing of GNP nanoparticles in the matrix of BECs improves the low velocity impact behavior of these composites by increasing the contact force and decreasing the absorbed energy in rebounding state. Finally, based on the experiments, the 0.5 wt.% BEC has the best impact performance by applying 15.08 kN impact force against the applied forces of 13.78 kN and 11.208 kN for 0.1 wt.% and pure BECs.

Spray-coating of graphene nanoplatelets on sisal fibers and its influence on electromechanical behavior of biocomposite laminates

Spray coating and vacuum-assisted resin infusion processes were implemented in this work to develop multifunctional biocomposite laminates. The biocomposites were fabricated using a bio-based epoxy resin reinforced with natural sisal fibers coated with graphene nanoplatelets (GNPs). A systematic characterization of material properties was performed to evaluate the mechanical, thermomechanical, electrical, and piezoresistive behavior of biocomposites with different GNPs contents (0, 1, 4, 6, and 8 wt.%). The mechanical tests revealed that adding GNPs to biocomposites has a slight positive effect on their flexural properties compared to the neat biocomposites (without GNPs). The electrical and thermomechanical tests showed that the electrical conductivity and glass transition temperature of biocomposites containing GNPs were enhanced significantly, achieving average values of 5.19 x 10-4 S/m and 63.29°C (26%), respectively. Regarding electromechanical tests, the biocomposites with 8 wt.% GNPs exhibited an excellent piezoresistive behavior under monotonic loading conditions, achieving a gage factor (strain sensitivity) of 3.56. Bending tests with cyclic loading were also performed, and cyclic reproducibility of the piezoresistive response of the biocomposites after 10 cycles was demonstrated, evidencing that the incorporation of GNPs onto sisal fibers by spray-coating produces an effective formation of conductive networks into biocomposites suitable for sensing applications.

Experimental validation of a new adaptable LCM mold filling software

Resin Transfer Molding (RTM) is a manufacturing process for fiber reinforced polymer composites where dry fibers are placed inside a mold and resin is injected under pressure. During mold design, filling simulations can study different manufacturing concepts (i.e. placement of injection gates and vents) to guarantee complete filling of the part and avoid air entrapment where flow fronts converge. In this work, a novel software tool LCMsim, which was implemented by the authors, is benchmarked against other tools and real-world flow experiments. Its development was driven by two ideas: Easy-of-use for the mold engineer and maximum flexibility for the researcher. Two experiments were used for validation. In the first, zones with different preform properties were present and in the second, race-tracking was enforced. Flow fronts from LCMsim and experiment agree with 7% error and simulated flow fronts from LCMsim and the commercially available software PAM-RTM agree with 3% error.

Analysis of Sandwich Composite Manufacture with Triaxial-Processed Foam Core by Vacuum-Assisted Resin Infusion Moulding and Resin Reinforcement

Analysis of Sandwich Composite Manufacture with Triaxial-Processed Foam Core by Vacuum-Assisted Resin Infusion Moulding and Resin Reinforcement

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.

The influence of addition of carbon nanotube and graphene platelets on characteristics of carbon/basalt fiber reinforced intra‐ply hybrid composites

AbstractIn this study, effects of addition of carbon nanotubes (CNTs) and graphene platelets (GPLs) on characteristics of carbon/basalt fiber reinforced intra‐ply hybrid composites were investigated. The composites were fabricated using vacuum assisted resin infusion molding (VARIM) method in two types including bare and 0.1, 0.5 wt.% of GPL and CNT nanoparticles filled hybrid composites. Fabricated normal and multiscale composites were cut by water jet and mechanical properties of specimens were examined by tensile, flexural, SBS experiments. Therefore, the modulus of elasticity, flexural modulus, tensile and flexural strength and ILSS of bare and multiscale composites were compared. Thermomechanical properties of fabricated composites were evaluated by dynamic mechanic analyze (DMA), thermogravimetric analyze (TGA) and thermal conductivity (TC) tests and storage modulus, loss modulus, damping ratio, glass transition temperature, weight loss and derivative weight loss were compared in fabricated normal and multiscale composites. Similarly, modal properties of fabricated composites such as natural frequency and damping factor were obtained by vibrational tests and compared in fabricated composites. According to the results, the addition of carbon‐based nanoparticles improved the characteristics of carbon/basalt fiber intra‐ply hybrid composites. The response of composites was directly proportional to the addition ratio of the carbon‐based nanoparticles.

Reinforcement contribution of cellulose nanocrystals (CNCs) to tensile properties and fracture behavior of triaxial E-glass fabric/epoxy composites

Triaxial E-glass fabric/CNCs/epoxy composites were fabricated using the vacuum-assisted resin infusion procedure. CNCs/epoxy mixtures were prepared through dispersing various amounts of CNCs within two different mixing mediums, i.e., mixture of epoxy/curing agent (technique EC) and curing agent (technique C). The effects of mixing medium (curing agent vs resin system) and CNC concentration (0.125, 0.25 and 0.5 wt%) on tensile modulus, tensile strength and fracture toughness of the composite samples were evaluated as a novel theoretical attempt. Fracture behaviors of composite samples containing a circular hole were investigated based on energy method developed by Griffith & Irwin in fracture mechanics. Incorporation of 0.25 wt% CNCs within epoxy matrix via technique C yielded an increase of 21.1 % in fracture toughness. Enhancements in critical crack length (16.06 %) and critical energy release rate (88 %) of CNCs-modified composites through technique C propose additional energy absorption during fracture.

Interactive fiber-elastomer composites for locomotion mechanism

There is a considerable need for research to fully exploit the application potential of adaptive fiber-reinforced plastics based on functional materials, in particular with regard to industry-specific solutions. Hence, this paper presents the development of a locomotion mechanism based on fiber-elastomer composites with shape memory alloys. In order to attain this goal, shape memory alloys were textile-technically integrated into the reinforcing fabric in the weft direction using flat knitting technology. The functionalized reinforcing fabrics was infused by the vacuum assisted resin infusion with an elastomeric silicone matrix system. Later, an extensive electro-thermal-mechanical characterization of the fiber-elastomer composites by varying electrical power caused by the varying voltage amplitude was completed. The fiber-elastomer composites were then shaped in a cross-country ski as an example of locomotion mechanism. Finally, the forward movement of the cross-country skiers was realized by activating the shape memory alloy in the left and right leg.

Effect of fibre stacking orientation on the mechanical and thermal properties of laminated kenaf fibre/epoxy composites

ABSTRACT Natural fibre-reinforced composites have been developed by researchers and industries as a solution to reduce the use of synthetic fibres. Kenaf fibre is one of the most abundant natural fibres in Indonesia. This study aimed to obtain the mechanical and thermal properties of kenaf fibre-reinforced epoxy laminated composites fabricated using a vacuum-assisted resin infusion method. The alkaline-treated fibres were arranged in the orientations 0°/0°/0°/0° and 0°/90°/0°/90°. Density measurements, mechanical tests, and thermogravimetric analysis were carried out on the epoxy and the composites. The results of the mechanical testing showed that the tensile, flexural, and compression strengths of the kenaf fibre-reinforced epoxy composites with a 0°/0°/0°/0° fibre orientation were higher than those of the composites with a 0°/90°/0°/90° fibre orientation, with values of (96.61 ± 10.18) MPa, (131.01 ± 6.60) MPa, and (71.96 ± 5.50) MPa, respectively. Scanning electron microscope observations showed that the composites had good fibre-matrix adhesion. The thermal stability of the epoxy was enhanced from 557 °C to 571 °C by incorporating kenaf fibre with 0°/0°/0°/0° orientation. With reference to the Indonesian National Standard 01-4449–2006, the two composites could be classified as T2 45 High Density Fibreboard.

The Hybridization Effects of Glass and Carbon Fibers on the Mechanical Properties of Kenaf Mat/Epoxy Composites

ABSTRACT Kenaf mat/epoxy composite possesses low mechanical properties. The investigation examined the hybridization impact on the mechanical performance of kenaf mat/carbon/epoxy and kenaf mat/glass/epoxy hybrid composites. Pure and hybrid composites were fabricated using the vacuum-assisted resin infusion method. Density, tensile, flexural, interlaminar shear, and fracture toughness (Mode II) properties were tested according to the ASTM standards. The results showed that density increased around 10% for kenaf mat/carbon/epoxy hybrid and 29% for kenaf mat/glass/epoxy hybrid compared to pure kenaf mat/epoxy composites. Kenaf mat/carbon/epoxy hybrid composites displayed approximately 529%, 497%, 512%, 1055%, 272%, and 443% improvement in the tensile strength, tensile modulus, flexural strength, flexural modulus, interlaminar shear strength (ILSS), and fracture toughness, respectively, compared to the pure kenaf mat/epoxy composite. Kenaf mat/glass/epoxy hybrid composites displayed approximately 467%, 275%, 405%, 413%, 232%, and 366% improvement in the tensile strength, tensile modulus, flexural strength, flexural modulus, ILSS, and fracture toughness, respectively, compared to the pure kenaf mat/epoxy composite. Although the carbon fiber volume fraction was the lowest (17.23%) in hybrid kenaf mat/carbon/epoxy composites compared to glass fiber (24.83%) in hybrid kenaf mat/glass/epoxy composites, the tensile, flexural, and interlaminar shear performance was higher in hybrid kenaf mat/carbon/epoxy composites than hybrid kenaf mat/glass/epoxy composites.

Low velocity impact response of sandwich composites with hybrid glass/natural fiber face-sheet and PET foam core

Abstract The focus of this study is manufacture of sandwich composites using palm and jute natural fibers with E-glass due to their high specific advantages such as lightweight, thermal insulation strength, biodegradability characteristics. The sandwich composites using in this study were fabricated using vacuum assisted resin infusion molding (VARIM) technique. The palm, jute and E-glass fibers were used as reinforcing materials, and PET foam core having a thickness of 10 mm was used as a core material. All specimens were then subjected to low velocity impact tests under various impact energy levels of 20 J, 30 J, 40 J, 50 J, and 60 J at room temperature. Force-time and force-deflection diagrams, maximum contact forces, contact times, and deflections corresponding to the peak forces, and absorbed energies of sandwich composites were obtained for each impact energy level in detail. Damages of sandwich composites are shown for selected energies. According to the obtained results, it was found out that the sandwich composite fabricated with palm fiber has a superior impact behavior in terms of maximum contact force compared to other configurations of sandwich composite (i.e., neat E-glass and jute reinforced E-glass).

Monitoring of three-dimensional resin flow front using hybrid piezoelectric-fiber sensor network in a liquid composite molding process

In this paper, a hybrid piezoelectric-fiber sensor network is developed to monitor the three-dimensional resin flow front of thick composite parts in the vacuum assisted resin infusion (VARI) process. Three different approaches based on non-invasive and integrated piezoelectric lead-zirconate-titanate (PZT) sensor network are developed to detect the three-dimensional resin flow front globally. To check the location of the invisible three-dimensional flow front inside the preform, multiple fiber optic sensors are embedded as flow sensors in different layers. The measurements from the piezoelectric and fiber optic sensor networks are then combined as a complement of each other to estimate the three-dimensional resin flow front. The applicability of the proposed hybrid sensor network is investigated on a thick carbon fiber reinforced plastic specimen with three different thicknesses at different locations. Experimental results confirm that the hybrid piezoelectric-fiber sensor network is capable of successfully estimating the three-dimensional flow front in situ and in real-time, achieving smart health monitoring.

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.

On the effect of binders on interlaminar fracture energies and R-curves of carbon/epoxy laminates with non-woven micro-fibre veils

The effect of short micro-fibre-based veils on the mode-I and mode-II interlaminar fracture energies and R-curves of composite laminates is investigated in this study—with an emphasis on the role of veil binders. Non-woven polyphenylene sulfide veils with 10 g/m2 areal weight and two different binders (i.e. cross-linked styrene-acrylic and cross-linked polyester), and non-woven carbon veils with 10 g/m2 areal weight and four different binders (i.e. cross-linked styrene-acrylic, cross-linked polyester, polyester and polyvinyl alcohol) are used for interleaving composite laminates. Carbon/epoxy laminates are manufactured by vacuum-assisted resin infusion with out-of-autoclave curing. The mode-I and mode-II fracture behaviour of the laminates are investigated. The results show that the binders used in the manufacturing of veils can considerably affect the fracture energy, crack path and R-curve behaviour, and that the effect of binders is more pronounced in the laminates with carbon veils than in the laminates with PPS veils.

An experimental study on the effects of introducing carbon nanotube on low velocity impact behavior of carbon/aramid fiber reinforced intra-ply hybrid composites

In this research, the addition effects of Multi Wall Carbon Nanotube (MWCNT) on low velocity impact behavior of Carbon/Aramid Fiber Reinforced (CAFRP) intra-ply hybrid composites were studied. In this regard, three types of pure, 0.1 wt.% and 0.5 wt.% introduced CAFRP intra-ply hybrid composites were fabricated by Vacuum Assisted Resin Infusion Molding (VARIM) method. The profile energy method was used to determine the penetration and perforation threshold. The main purpose of this research was to improve the impact behavior of CAFRP by addition of MWCNT to the matrix of these composites. The low velocity impact test was also carried out in 30, 50, 80 and 120 J energy values. The effect of addition MWCNTs in the matrix of composite was investigated by plotting force, absorbed energy and deflection vs. time and the key parameters of impact test such as maximum contact force, absorbed energy, deflection and duration time were compared for pure and multi scale CAFRP composited. According to the results, the addition of MWCNT improved the low velocity impact behavior of CAFRP intra-ply hybrid composites by not only increasing the toughness of epoxy matrix but also upgrade the adhesion of carbon fibers to the epoxy matrix. It was also found that fiber breakage, fiber pull out, matrix cracking, delamination and fiber matrix debonding were the most important failure modes in these types of tested composites.

Experimental study of low-velocity impact behavior and damage characteristics of flat-knitted spacer fabrics reinforced composites

Flat-knitted spacer fabrics are three-dimensional fabrics with good formability and impact resistance, which can be rapidly produced complicated shape preforms. In this work, low-velocity impact behavior and damage characteristics of flat-knitted spacer fabrics reinforced composites were studied and the mechanism of the effects of spacer yarn structure on the impact properties of the composites were explored. Flat-knitted spacer fabrics with three spacer structures were produced using ultrahigh molecular weight polyethylene (UHMWPE) filaments, and composite plates were prepared by vacuum-assisted resin infusion. Low-velocity impact tests were carried out using a drop-weight impact testing machine equipped with a hemispherical impactor. It was revealed that the impact process of the flat-knitted spacer fabrics reinforced composites could be divided into three areas. The effect of initial impact energy on the impact properties of the sample was mainly reflected in the damage speed and initial damage threshold in the first areas. With the increase of spacer yarn span, the damage tolerance, stiffness, and impact resistance of the composite were also increased. Besides, the main damage mechanism of flat-knitted spacer fabric reinforced composites was plastic deformation, matrix fracture, fiber-matrix debonding, and tow splitting.