Vacuum Assisted Resin Infusion Research Articles

A Comparative Study on Mechanical Properties of Kenaf Fiber-Reinforced Polyester Composites Prepared by VARI, RTM and CM Techniques

This work aims at comparing the mechanical properties of composite laminate fabricated by three different fabrication processes. Kenaf fiber polyester composite laminates were fabricated by compression moulding technique, Vacuum assisted resin infusion process (VARI) and Resin transfer moulding process (RTM). Vacuum assisted resin infusion (VARI) process bridges the gap between labour intensive compression moulding process and capital intensive Resin transfer moulding (RTM) process. The mechanical properties such as tensile, flexural and impact behaviour were studied. Vacuum assisted resin infusion process showed improved tensile and flexural strength as compared to resin transfer moulding process and compression moulding (CM) process. On the other hand, impact strength of VARI composites is slightly lower than that of RTM and CM composites. From the study, it was found that mechanical properties increase with increase in fiber content and uniform distribution of resin in the matrix. The void content and water absorption properties were evaluated and found to be maximum for the compression moulded composites.

Investigation of mechanical properties and failure surfaces of adhesively bonded composites subjected to vibration loads

The effect of cyclic-vibration-loading on adhesively bonded joints that made from laminated composites was investigated in this study. Eight layered fiber glass composite plates were produced via vacuum assisted resin infusion method and the composite plates fixed at both ends were vibrated under different vibration cycles after they were bonded single lap adhesively. Then, the tensile test was carried out to determine the ultimate load and to evaluate the joint performance and failure of E/glass-epoxy composites. The results showed that the ultimate load capacity and absorbed energy of joint decreased by increasing vibration load cycles. In addition, after the tensile test, the surfaces of the adherends were examined and it was observed that fiber failure increased with the increasing of the vibration cycle and grooves of the fibers occurred.

Processing high-performance woody materials by means of vacuum-assisted resin infusion technology

High-performance materials derived from natural wood have been vigorously developed, however, their commercialized products are very limited owing to the lack of industrial production efficiency and increase of environmental concern. This study is aimed at developing a clean process for large-scale production of high-performance woody materials without involving any chemical methods. The industrialized vacuum-assisted resin infusion (VARI) process was initially applied to solid wood for manufacturing woody materials with excellent flexural performances. VARI process can provide better control over harmful volatiles generated by resins than that of the traditional open mold techniques, making them compliant with “clean production”. The porosity was reduced from 66.0% to 33.8% after infusing epoxy into wood through the VARI process, and further reduced to 22.6% after being compressed. The flexural modulus and strength were significantly increased by 142.2% and 142.8%, respectively. The flexural strength (304.9 MPa) reached the range of alloy, between Alloy 2024-T3 (345 MPa) and Steel alloy 1040 (260 MPa). Due to its relatively low density, the specific flexural strength was only slightly lower than diamond. The dramatic reduction of porosity was deemed to be the major contribution to those improvements. The fabrication of high-performance woody materials does not use chemical treatment; therefore, it could be considered as a clean production. Additionally, the contribution to clean production of this study was further confirmed by life-cycle assessment (LCA). The comparisons of environmental impacts of the woody material, steel alloy and aluminum alloy were carried out using LCA, revealing that the global warming, acidification, human health (HH) cancer, HH noncancer, HH criteria air pollutants, eutrophication, ecotoxicity, smog, natural resource depletion, habitat alteration, and ozone depletion, were reduced by 1.72–667.06 times when the woody material was used to replace steel alloy, while were reduced by 7.34–636.21 times when the woody material was utilized to replace aluminum alloy, respectively.

Mechanical response of adhesively bonded composite joints subjected to vibration load and axial impact

In the present work, the effects of vibration and impact on the mechanical performance of adhesively bonded joint of fiber-reinforced plastic (FRP) composite structures were investigated experimentally, and the main failure modes were discussed. For this purpose, eight layered fiberglass composite plates were produced using vacuum assisted resin infusion technique. DP-460 adhesive was used for the joining of composite plates. In order to study the joint performance, the tensile test was carried out on adhesively bonded specimens subjected to vibration and impact. The changing parameters for this investigation are the number of vibration cycles and level of axial impact energy. Experimental results indicate that the vibration and impact have a great effect on joint strength. However, this effect is not always negative in contrary to the expected behavior. Certain values of impact load and vibration cycles applied to the joint improve the tensile strength of the adhesively bonded joint. This result shows a complex interaction between the composite plate and adhesive through the dynamic loading. This work provided a new approach to increase the mechanical properties of adhesively bonded joints applying the dynamic loads.

Effects of Fiber Surface Grafting with Nano-Clay on the Hydrothermal Ageing Behaviors of Flax Fiber/Epoxy Composite Plates.

Flax fiber has high sensitivity to moisture, and moisture uptake leads to the decrease of mechanical properties and distortion in shape. This paper attempts to graft flax fabric with nano-clay, with assistance from a silane-coupling agent, in order to improve hygrothermal resistance. The nano-clay grafted flax fabric reinforced epoxy (FFRP) composite produced through vacuum assisted resin infusion (VARI) process were subjected to 80% RH chamber for 12 weeks at 20, 40 and 70 °C, respectively. Moisture uptake, dimensional stability, and tensile properties was studied as a function of humidity exposure. Through SEM and FTIR, the effects of hygrothermal exposure was elucidated. In comparison to control FFRP plates, nano-clay grafting decreases saturation moisture uptake and the coefficient of diffusion of FFRP by 38.4% and 13.2%, respectively. After exposure for six weeks, the retention rate of the tensile modulus of the nano-clay grafted flax fiber based FFRP increased by 33.8% compared with that of the control ones. Nano-clay grafting also reduces the linear moisture expansion coefficient of FFRPs by 8.4% in a radial direction and 10.9% in a weft direction.

An objective comparison of common vacuum assisted resin infusion processes

This study executed an objective comparison between Resin Infusion methods currently used, providing a level comparison in identical circumstances. Six different resin infusion methods including VARTM, SCRIMP, CAPRI, DBVI, VAP, and PI were investigated to discern if the modifications made relevant to the standard VARTM process have a distinguishable effect, and how significant the effect was. Process parameters were found to vary significantly between methodologies, with large differences in infusion time, laminate pressure and relaxation, and resin usage. Fibre volume fractions were found to vary significantly both between methodologies and along the infusion length of some panels. Differences of up to 13% and 10% were found in short beam strength and compression strength between the infusion methods. There was found to be no significant difference in void content between methodologies once the best process parameters had been established, with the exception of PI which resulted in a significant increase.

One-step electrodeposition of Cu/CNT/CF multiscale reinforcement with substantially improved thermal/electrical conductivity and interfacial properties of epoxy composites

A novel copper/carbon nanotube/carbon fiber (Cu/CNT/CF) multiscale reinforcement was successfully achieved using a one-step electrophoretic deposition technique in which CNT was introduced via two techniques. Two stabilized electrolytes containing CNT of distinct charge character were prepared to investigate the effect of CNT to the thermal/electrical conductivity and interlaminar shear strength (ILSS) of the composites. The positively charged CNT composites showed increases of 359.2%, 2761% and 34.5% for thermal conductivity and electrical conductivity in the through-thickness direction and the ILSS, respectively, in comparison with de-sized CF composites. Contrast with the two-step method, the preparation time of the one-step method has been shortened to one-fifth, and the connections between the Cu and CNT were compacted to improve the conductivity of the composites. Moreover, Cu/CNT/CF prepared according to the one-step method was highly compatible with vacuum-assisted resin infusion technology and provided a route for preparing multifunctional composites that could be easily scaled up.

Mechanical properties and failure modes of hybrid fiber reinforced polymer composites with a novel liquid thermoplastic resin, Elium®

In virtue of recyclability purposes, higher impact and damage tolerance properties, efficient and ease of fabrication, a new liquid Methyl Methacrylate (MMA) thermoplastic resin, Elium® 188, has been recently developed. This new resin can replace (epoxy) thermoset-based resins for the fabrication of laminates at room temperature with equivalent mechanical properties. Plain weave ultra-high molecule weight polyethylene fiber (UHMWPE), carbon fiber, and their hybrid systems are fabricated by Vacuum Assisted Resin Infusion (VARI) method at ambient temperature. ASTM standard tests of tensile, compression, and shear (both intralaminar and interlaminar) are conducted to determine the mechanical properties with the aim of comparing the results with those of thermosets. Fractographic analyses are performed to have a better understanding of the behavior of these new thermoplastic-based laminates. The test results show the mechanical properties of thermoplastic-based laminates are comparable to those thermoset-based but with the aforementioned advantages, leading to wider applications in the industry.

Low velocity impact behavior of interlayer hybrid composite laminates with carbon/glass/basalt fibres

This work investigates the effects of carbon/glass/basalt hybridization and fabric structure on the low velocity impact resistance of fibre reinforced plastic composites. Interply hybrid specimens used in the study were fabricated in a sandwich-like stacking sequence using a vacuum assisted resin infusion molding technique. Low velocity impact tests were carried out to study the effects of hybridization and fabric structure on the impact resistance of composite laminates. A continuum damage mechanical model was developed and validated for non-hybrid woven fabric laminates at different impact energy levels. Residual damage characteristics were identified using a 3D surface scanning system and an X-ray computed tomography (CT) method. On the basis of the experimental results, numerical simulation was also conducted to explore the damage mechanisms of the hybrid laminates. The study showed that: (a) hybrid laminates with carbon fibre as the core exhibited superior impact resistance for sandwich-like stacking sequence; (b) similar impact behaviors appeared for carbon laminates hybridised with either basalt or glass fibre; (c) for basalt fibre, weave fabric composite laminates exhibited better energy absorption capability and deformation resistance than cross-ply laminates reinforced in unidirectional fabrics.

The Failure Mechanism of Composite Stiffener Components Reinforced with 3D Woven Fabrics.

Composite industry has long been seeking practical solutions to boost laminate through-thickness strengths and interlaminar shear strengths (ILSS), so that composite primary structures, such as stiffeners, can bear higher complex loadings and be more delamination resistant. Three dimensional (3D) woven fabrics were normally employed to render higher transverse and shear strengths, but the difficulty and high expense in producing such fabrics make it a hard choice. Based on a novel idea that the warp yarns that interlock layers of the weft yarns might provide adequate fiber crimps that would allow the interlaminar shear or radial stresses to be transferred and borne by the fibers, rather than by the relatively weaker matrix resin, thus improving the transverse strengths, this work provided a two point five dimensional (2.5D) approach as a practical solution, and demonstrated the superior transverse performances of an economical 2.5D shallow-bend woven fabric (2.5DSBW) epoxy composites, over the conventional two dimensional (2D) laminates and the costly 3D counterpart composites. This approach also produced a potential candidate to fabricate high performance stiffeners, as shown by the test results of L-beams which are common structural components of any stiffeners. This study also discovered that an alternative structure, namely a 2.5D shallow-straight woven fabric (2.5DSSW), did not show any advantages over the two control structures, which were a 2D plain weave (2DPW) and a 3D orthogonal woven fabric (3DOW) made out of the same carbon fibers. Composites of these structures in this study were conveniently fabricated using a vacuum-assisted resin infusion process (VARI). The L-beams were tested using a custom-made test fixture. The strain distribution and failure mode analysis of these beams were conducted using Digital Image Correlation (DIC) and X-ray Computed Tomography Scanning (CT). The results demonstrated that the structures containing Z-yarns or having high yarn crimps or waviness, such as in cases of 3DOW and 2.5DSBW, respectively, were shown to withstand high loadings and to resist delamination, favorable for the applications of high-performance structural composites.

Intra‐laminar toughening mechanisms to enhance impact damage tolerance of 2D woven composite laminates via yarn‐level fiber hybridization and fiber architecture

AbstractAdvanced composites are widely used in primary and secondary structural applications, for example, aerospace, automotive, marine, and renewable energy sectors. But it is well recognized that the impact resistance and damage tolerance of composite laminates are in general poor, which is a major challenge for optimizing structural designs. In this regard, an experimental study is conducted for enhancing the damage tolerance of 2D woven composite laminates by exploring yarn‐level fiber hybridization. Hybrid yarns are produced by combing high‐strength fibers, that is, S‐glass, and high‐toughness fibers, that is, polypropylene [PP], and using commingling and core‐wrapping processes. Using the hybrid yarns, 2D fabrics, that is, with 5H satin, 2/2 twill, and 2/2 basket architectures, are weaved, and subsequently hybrid S‐glass/PP/epoxy laminates are manufactured via vacuum assisted resin infusion. The low velocity impact response and energy absorption of the hybrid laminates are investigated by drop‐weight impact tests at different energy levels, that is, 15 J, 25 J, 35 J, and 50 J. The damage tolerance is studied by compression‐after‐impact (CAI) tests, measuring the residual compressive strength of the damaged laminates. Furthermore, the failure modes are investigated using scanning electron microscopy for identifying damage mechanisms in the hybrid laminates after the impact and CAI tests. The impact response and damage tolerance of the 5H satin, 2/2 twill, and 2/2 basket fabric laminates are compared with that of noncrimp‐fabric laminates produced with (ie, S‐glass/PP yarns) and without (ie, S‐glass yarns) yarn‐level hybridization. It is shown that yarn‐level hybridization and fiber architecture significantly affect the impact behavior and damage tolerance of the 2D woven S‐glass/PP/epoxy hybrid laminates investigated. The microscopy studies show that intra‐yarn, inter‐yarn, inter‐lamina failure mechanisms can in general be introduced by combining yarn‐level fiber hybridization and fiber architecture for modifying failure and energy dissipation mechanisms under low velocity impact and hence the damage tolerance of composite laminates.

Towards balancing in-plane mechanical properties and impact damage tolerance of composite laminates using quasi-UD woven fabrics with hybrid warp yarns

An experimental study is conducted with the aim of balancing in-plane mechanical properties and impact damage tolerance in composite woven laminates using a quasi-unidirectional (quasi-UD) woven fabric (i.e. low crimp architecture) and yarn-level fibre hybridisation. In this work, composite laminates are manufactured with and without yarn-level hybridisation and yarn crimp. By combining high-strength fibres (i.e. S-glass) and high-elongation fibres (i.e. polypropylene, PP) with commingling and core-wrapping processes, hybrid S-glass/PP yarns are produced. A quasi-UD fabric is then produced with unbalanced warp and weft yarns (i.e. 5H satin with high linear density hybrid S-glass/PP warp and low linear density S-glass weft yarns), and subsequently laminates are manufactured using vacuum-assisted resin infusion. In addition, hybrid S-glass/PP yarns are used to manufacture non-crimp (i.e. without weft yarns) and 5H satin fabric (i.e. with balanced S-glass/PP warp and weft yarns) laminates. For comparison, S-glass yarns are used to manufacture non-crimp cross-ply laminates (i.e. without yarn-level hybridisation and without weft yarns). For all the laminates, the in-plane mechanical properties are measured by using tensile and compressive tests, and the low velocity impact response is investigated using drop-weight impact tests with different energy levels (i.e. 15, 25, 35 and 50 J). Furthermore, the impact damage tolerance is characterised by measuring residual compressive strengths with compression-after-impact tests. The damaged specimens are investigated using scanning electron microscopy to identify inter- and intra-laminar failure mechanisms. The results indicate that the quasi-UD woven fabric composites with low crimp and yarn-level hybridisation can be successfully used to introduce conducive fibre architecture and microstructures to balance in-plane mechanical properties and impact damage tolerance.

Low velocity impact behaviour of recycled mussel shell particles reinforced epoxy composites

In this study, low velocity impact behaviour of the recycled mussel shell particles reinforced epoxy composites experimentally investigated. This study is a new part of a continuous research, which aims to protect the environment against pollution of the waste mussel shells. The mussel shells that were used in the study are biologically defined as Mediterranean mussels. The waste mussel shells recycled by a hammer and a rod mill, respectively. A particle size analysis was done for the recycled mussel shells. According to the particle size analysis results mean diameter of the particles are 74 μm with 64 μm standard deviation. Particle reinforced epoxy composite was produced as a plate by vacuum assisted resin infusion molding method. After resin impregnation process finished, curing process started at 80 °C for 8 h. Dimensions of the produced composite plate was 650 mm × 310 mm × 10 mm (length × width × thickness). Then, impact specimens were cut from the plate at the dimensions of 100 mm x 100 mm × 10 mm (length × width × thickness) by a table saw machine. Low velocity impact tests were conducted for five specimens for 40 J impact energy. The recycled mussel shell particles reinforced polymeric composite materials showed maximum 36 J absorbed energy according to the test results. Finally, the morphology and the failure modes of the new composites were given in macro and micro scale by the scanning electron microscope analysis, respectively. In conclusion, waste mussel shells have good impact resistance to be used as a reinforcement material in polymeric composites. Moreover, using waste mussel shells in a production is an effective way to protect environmental pollution.

Sampling phased array technology for the detection of voids in carbon fiber-reinforced plastics

In the lightweight material industries, the current focus is on fiber-reinforced plastics, in particular on carbon fiber-reinforced plastics (CFRPs), since they offer higher relative specific tensile strength and stiffness as well as reduced weight compared to conventional metallic materials. Currently, the quality assurance of manufactured CFRP components represents a major challenge for CFRP manufacturers. Voids are generated during the infusion process of CFRPs, which in turn reduce the mechanical performance of CFRPs. This article presents the possibility to detect the distribution of voids across the surface of CFRPs by using a non-destructive testing method, the so-called sampling phased array ultrasound technology. Two types of CFRPs with six carbon layers in the same direction are fabricated by means of a vacuum-assisted resin infusion process. Voids in CFRPs are generated using a foaming agent during the impregnation process. The C-scan images produced through the sampling phased array technology are subsequently analyzed by the optical image analysis software in order to determine the amount of voids for each type of manufactured CFRP.

The Effect of Thermal Shock Cycling on Low Velocity Impact Behavior of Carbon Fiber Reinforced Epoxy Composites

In this research, we investigated the effect of temperature variation on low velocity impact response of woven carbon fiber reinforced polymer (CFRP) composites. Carbon fibers were weaved in twill 2/2 type and they reinforced the composite performance. We applied epoxy as composite matrix and then fabricated CFRP plates by using vacuum assisted resin infusion molding (VARIM) method. We performed thermal cycling shock experiment between – 40 and + 120 °C for 20, 40, 60 and 80 cycles. Then, we exposed specimens to the low velocity impact test for various thermal cycling numbers. The results showed that thermal cycling shock can improve or degrade the impact behavior based on post curing and debonding processes. Debonding possibly occurred since there was a coefficient of thermal expansion (CTE) mismatch between composite components. We also observed that the (room temperature tested) RT samples and the samples exposed to 80 cycles between – 40 and + 120 °C had the best and weakest performance, respectively. Finally, the increase of cycle numbers in thermal shock cycling process degraded the composite structure and decreased the impact performance of CFRPs.

PENGARUH VARIASI JUMLAH LAPISAN FIBERGLASS DAN ANYAMAN BAMBU TERHADAP KEKUATAN BENDING KOMPOSIT DENGAN METODE VACUUM ASSISTED RESIN INFUSSION (VARI)

The objective of this research is to obtain the bending properties of composite material produced by VARI method, and to get analysis of polyester resin distribution time on the layer of fiberglass composite and bamboo woven strip.The process of making composites varies, but the process of making this research is the process of Vacuum Assisted Resin Infusion (VARI). In the VARI process, dry fiber is placed between the fixmold and plactic bag, then the resin is injected after the chamber inside the low- pressure plastic bag and the process continues until all parts of the fiber are wetted by the resin.From the results of research, testing and discussion of bending test results that have been done then can be drawn conclusions include: Variation of the number of reinforcement layer on VARI method will affect the value of bending strength of composite. By using the VARI method The highest average value of bending stress occurs in variation 4 (206,69 MPa), while the lowest occurs in variation 1 (42,83 MPa), and the time required for the distribution of resin varies in time variation 1 which takes 5 minutes 02 seconds, while for variation 4 takes 8 minutes 3 seconds.Keywords: composites, VARI method, glass fiber, bending test

Preparation and Mechanical Properties of Graphene/Carbon Fiber-Reinforced Hierarchical Polymer Composites

Conventional carbon fiber-reinforced plastics (CFRP) have extensively been used as structural elements in a myriad of sectors due to their superior mechanical properties, low weight and ease of processing. However, the relatively weak compression and interlaminar properties of these composites limit their applications. Interest is, therefore, growing in the development of hierarchical or multiscale composites, in which, a nanoscale filler reinforcement is utilized to alleviate the existing limitations associated with the matrix-dominated properties. In this work, the fabrication and characterization of hierarchical composites are analyzed through the inclusion of graphene to conventional CFRP by vacuum-assisted resin infusion molding.

Mechanical Behaviors of Flax Fiber-Reinforced Composites at Different Strain Rates and Rate-Dependent Constitutive Model.

Flax fiber-reinforced composites (FFRCs) exhibit excellent environmentally friendly qualities, such as light weight, low cost, recyclability, and excellent mechanical properties. Understanding the dynamic mechanical behavior of FFRCs could broaden their potential applications in lightweight, crashworthy, and impact-critical structures. This study presents a study on the fabrication of FFRCs by vacuum-assisted resin infusion. The dynamic stress–strain responses of the fabricated specimens at strain rates ranging from 0.006 to 2200 were evaluated using quasi-static tests and the Split–Hopkinson pressure bar (SHPB). The results indicated that the FFRC exhibited superior strain rate sensitivity. Final deformation photographs and scanning electron micrographs clearly revealed the damage evolution of the FFRC specimens, as well as various failure mechanisms, including fiber–matrix debonding, fiber pull-out, and fiber fracture at different strain rates. On the basis of the experimental results, a simplified Johnson–Cook model was established to describe the strain-rate dependent constitutive model of FFRC. The validation of the suggested constitutive model was embedded in the finite element simulations and could well repeat the strain wave observed from the experiment results. Finally, the quasi-static compression and drop-hammer impact of pyramidal lattice structures with FFRC cores were investigated both numerically and experimentally, proving the effectiveness of the simplified Johnson–Cook model. This study could potentially contribute to a deeper understanding of the dynamic mechanical behavior of FFRCs and provide fundamental experimental data for future engineering applications.

Manufacturing and mechanical performances of a novel foam core sandwich-walled hollow column reinforced by stiffeners

To obtain a strong and weight-efficient cylindrical column, we proposed a novel foam core sandwich-walled hollow column reinforced by stiffeners (FSCRS). The FSCRS was consisted of glass fibre-reinforced polymer (GFRP) faces, polyvinyl chloride (PVC) foam core, and GFRP stiffeners. Four full-diameter specimens, including two FSCRS and two traditional foam core sandwich-walled hollow columns (FSC), were manufactured using a vacuum-assisted resin infusion (VARI) process. Axial compression tests were carried out to reveal the mechanical behaviours of the FSC and FSCRS. Experiments showed that, benefitting from the combination advantage of stiffened cylinder and sandwich cylinder, this novel FSCRS can resist or postpone various buckling failure, instead of failing via face crushing with high strength. Compared to FSC, the load-mass ratio of FSCRS increased markedly by 48.3% and 50.1% for specimen face thickness of 1.2 and 2.4 mm, respectively. Combined with the cost-effective manufacturing technology, the novel FSCRS is a desirable alternative to achieve superior compression properties required in engineering structures.

Strain energy release rate of sandwich composite beams for different densities and geometry parameters

In this paper, fracture behaviour of marine sandwich structured composite beams manufactured by vacuum-assisted resin infusion process with a PVC foam core, and different thicknesses of upper and lower glass fibre-reinforced polymer face sheets have been investigated. Fracture toughness in terms of strain energy release rate of sandwich composite beam is obtained using three end notched flexure test (3 ENF) by analytical method, finite element simulation using J integral and virtual crack closure technique (VCCT). Experimental testing has been applied with more accurate loading values for finite element modelling (FEM) simulations. The good agreement between experimental and numerical results shows that the finite element model is acceptable. A parametric study is carried out to observe the effects of core thickness, density of core, length of specimens, loading directions of the specimens on strain energy release rate (SERR) of sandwich composite beams under mode II loading. It is developed for the different core thicknesses with varying density combinations. The variations of maximum SERR value are presented graphically using numerical method and compared with analytical solution.