Effect of linear density and yarn structure on the mechanical properties of ramie fiber yarn reinforced composites

Effects of linear density and yarn structure on both static and dynamic mechanical properties of ramie fiber yarn reinforced composites (RYRCs) were investigated. The failure mechanisms of RYRCs were analyzed with the aid of ultrasonic C-scan and Scanning electronic microscopy (SEM). The results showed that the tensile strength of RYRCs increased gradually with increase of the linear density of the single yarns. The maximum tensile strength was obtained when the linear density reached 67.3 tex. However, a downtrend of the tensile strength was observed with further increase of the linear density of ramie single and plied yarns. The interlaminar fracture toughness was relatively high for RYRCs made from yarns with lower linear density due to the extensive fiber bridging observed during the double cantilever beam test. Meanwhile, the linear density and structure of ramie yarn had remarkable influence on the failure mode of RYRCs during the drop weight impact test.     

A short review on basalt fiber reinforced polymer composites

A recent increase in the use of ecofriendly, natural fibers as reinforcement for the fabrication of lightweight, low cost polymer composites can be seen globally. One such material of interest currently being extensively used is basalt fiber, which is cost-effective and offers exceptional properties over glass fibers. The prominent advantages of these composites include high specific mechano-physico-chemical properties, biodegradability, and non-abrasive qualities to name a few. This article presents a short review on basalt fibers used as a reinforcement material for composites and discusses them as an alternative to the use of glass fibers. The paper also discusses the basics of basalt chemistry and its classification. Apart from this, an attempt to showcase the increasing trend in research publications and activity in the area of basalt fibers is also covered. Further sections discuss the improvement in mechanical, thermal and chemical resistant properties achieved for applications in specific industries.     

Layered silicates nanocomposite matrix for improved fiber reinforced composites properties

Three-phase glass fiber reinforced composites (GFRP) consisting of traditional woven glass fiber and polyamide-6 (PA6) matrix dispersed with organically modified layered silicates were prepared and investigated in this study. The fabrication of GFRP with different weight percentages of layered silicates was successful when the matrix contains less than 5 wt% of the layered silicates. The improvement due to the high aspect ratio and high stiffness of the layered silicates is illustrated through the matrix-controlled properties of the GFRP. The results showed that the GFRP with 5 wt% layered silicates offer the largest improvement of approximately 30% increase in both flexural strength and compressive strength at elevated temperatures. On the other hand, the in-plane shear properties measured from [±45]_s laminates revealed that the layered silicates help improved both the in-plane shear strength and modulus appropriately. By utilizing a nanocomposite matrix, improvement of stiffness and strength, as well as thermal and barrier properties is obtained without any change in processing temperature of the fiber composites.     

Tensile and flexural properties of snake grass natural fiber reinforced isophthallic polyester composites

Natural fiber composite materials are one such capable material which replaces the conventional and synthetic materials for the practical applications where we require less weight and energy conservation. The present paper, which emphasis the importance of the newly identified snake grass fibers which are extracted from snake grass plants by manual process. In this paper, the tensile properties of the snake grass fiber are studied and compared with the traditionally available other natural fibers. The mixed chopped snake grass fiber reinforced composite is prepared by using the isophthallic polyester resin and the detailed preparation methodology is presented. Fiber pull-outs on the fractured specimen during the physical testing of the composites are also investigated. The experimental evidence also shows that the volume fraction increases the tensile, flexural strength and modulus of the snake grass fiber reinforce composite.     

Study on the mechanical properties and thermal properties of jute and banana fiber reinforced epoxy hybrid composites

The aim of the present study is to investigate and compare the mechanical and thermal properties of raw jute and banana fiber reinforced epoxy hybrid composites. To improve the mechanical properties, jute fiber was hybridized with banana fiber. The jute and banana fibers were prepared with various weight ratios (100/0, 75/25, 50/50, 25/75 and 0/100) and then incorporated into the epoxy matrix by moulding technique to form composites. The tensile, flexural, impact, thermal and water absorption tests were carried out using hybrid composite samples. This study shows that addition of banana fiber in jute/epoxy composites of up to 50% by weight results in increasing the mechanical and thermal properties and decreasing the moisture absorption property. Morphological analysis was carried out to observe fracture behavior and fiber pull-out of the samples using scanning electron microscope.     

Effect of fiber arrangement on mechanical properties of short fiber reinforced composites

The present paper developed a three-dimensional (3D) “tension–shear chain” theoretical model to predict the mechanical properties of unidirectional short fiber reinforced composites, and especially to investigate the distribution effect of short fibers. The accuracy of its predictions on effective modulus, strength, failure strain and energy storage capacity of composites with different distributions of fibers are validated by simulations of finite element method (FEM). It is found that besides the volume fraction, shape, and orientation of the reinforcements, the distribution of fibers also plays a significant role in the mechanical properties of unidirectional composites. Two stiffness distribution factors and two strength distribution factors are identified to completely characterize this influence. It is also noted that stairwise staggering (including regular staggering), which is adopted by the nature, could achieve overall excellent performance. The proposed 3D tension–shear chain model may provide guidance to the design of short fiber reinforced composites.     

Evaluating the mechanical properties of reinforced LDPE composites made with carbon fibres recovered via solvothermal processing

Carbon fibre was recovered from a thermoset composite via a solvo-thermal process and used as reinforcement in low density polyethylene (LDPE). The oxidized recovered carbon fibres have shown better properties than original non-oxidized fibres. The best interactions between the continuous and dispersed phases were found using 3-aminopropyl-trimetoxysilane and experimentally synthesized polyalkenyl-polymaleic anhydride based polymers. The tensile strength of the prepared composites nearly doubled when 3-aminopropyl-trimetoxysilane was used as compatibilizer, in comparison to the composites prepared without additives. Based on infrared analysis, a chemical reaction has been proposed between –COOH groups of compatibilizers and the –OH groups of the carbon fibre surface for the best composites.     

Effect of fiber loading on the properties of treated cellulose fiber-reinforced phenolic composites

The effect of fiber loading on the properties of treated cellulose fiber-reinforced phenolic composites was evaluated. Alkali treatment of the fibers and reaction with organosilanes as coupling agents were applied to improve fiber–matrix adhesion. Fiber loadings of 1, 3, 5, and 7 wt% were incorporated to the phenolic matrix and tensile, flexural, morphological and thermal properties of the resulting composites were studied. In general, mechanical properties of the composites showed a maximum at 3% of fiber loading and a uniform distribution of the fibers in such composites was observed. Silane treatment of the fibers provided derived composites with the best thermal and mechanical properties. Meanwhile, NaOH treatment improved thermal and flexural properties, but reduced tensile properties of the materials. Therefore, the phenolic composite containing 3% of silane treated cellulose fiber was selected as the material with optimal properties.     

Thermal and dynamic mechanical analysis of polystyrene composites reinforced with short sisal fibres

The thermal behaviour of polystyrene composites reinforced with short sisal fibres was studied by means of thermogravimetric and dynamic mechanical thermal analysis. The thermal stability of the composites was found to be higher than that of sisal fibre and the PS matrix. The effects of fibre loading, fibre length, fibre orientation and fibre modification on the dynamic mechanical properties of the composites were evaluated. Fibre modifications were carried out by benzoylation, polystyrene maleic anhydride coating and acetylation of the fibre and the treatments improved the fibre-matrix adhesion. PS/sisal composites are thermally more stable than unreinforced PS and sisal fibre. The addition of 10% fibre considerably increases the modulus but the increase is found to level off at higher fibre loadings. The T_g values of the composites are lower than that of unreinforced PS and may be attributed to the presence of some residual solvents in the composites entrapped during the composite preparation. The treated-fibre composites show better properties than those of untreated-fibre composites. The Arrhenius relationship has been used to calculate the activation energy of the glass transition of the composites. A master curve is constructed based on time-temperature superposition principle.     

Mechanical properties of cellulose nanofiber (CNF) reinforced polylactic acid (PLA) prepared by twin screw extrusion

The aim of this study was to develop cellulose nanofiber (CNF) reinforced polylactic acid (PLA) by twin screw extrusion. Nanocomposites were prepared by premixing a master batch with high concentration of CNFs in PLA and diluting to final concentrations (1, 3, 5 wt.%) during the extrusion. Morphology, mechanical and dynamic mechanical properties (DMA) were studied theoretically and experimentally to see how different CNF concentrations affected the composites’ properties. The tensile modulus and strength increased from 2.9 GPa to 3.6 GPa and from 58 MPa to 71 MPa, respectively, for nanocomposites with 5 wt.% CNF. The DMA results were also positive; the storage modulus increased for all nanocomposites compared to PLA; being more significant in the high temperature region (70 °C). The addition of nanofibers shifted the tan delta peak towards higher temperatures. The tan delta peak of the PLA shifted from 70 °C to 76 °C for composites with 5 wt.% CNF.     

Aramid fibers reinforced silica aerogel composites with low thermal conductivity and improved mechanical performance

Aramid fibers reinforced silica aerogel composites (AF/aerogels) for thermal insulation were prepared successfully under ambient pressure drying. The microstructure showed that the aramid fibers were inlaid in the aerogel matrix, acting as the supporting skeletons, to strengthen the aerogel matrix. FTIR revealed AF/aerogels was physical combination between aramid fibers and aerogel matrix without chemical bonds. The as prepared AF/aerogels possessed extremely low thermal conductivity of 0.0227 ± 0.0007 W m⁻¹ K⁻¹ with the fiber content ranging from 1.5% to 6.6%. Due to the softness, low density and remarkable mechanical strength of aramid fibers and the layered structure of the fiber distribution, the AF/aerogels presented nice elasticity and flexibility. TG–DSC indicated the thermal stability reaching approximately 290 °C, can meet the general usage conditions, which was mainly depended on the pure silica aerogels. From mentioned above, AF/aerogels present huge application prospects in heat preservation field, especially in piping insulation.     

Tensile and thermomechanical properties of short carbon fiber reinforced polyamide 6 composites

In this study, carbon fiber (CF) reinforced polyamide 6 (PA6) composites were prepared by using melt mixing method. Effects of fiber length and content, on the mechanical, thermal and morphological properties of CF reinforced PA6 composites were investigated. Fiber length distributions of composites were also determined by using an image analyzing program. It was seen that the maximum number of fibers were observed in the range of 0–50 μm. Mechanical test results showed that, increasing CF content increased the tensile strength, modulus and hardness values but decreased strain at break values of composites. DSC results showed that T_g and T_m values of composites were not changed significantly with increasing CF content and length. However, heat of fusion and the relative degree of crystallinity values of composites decreased with ascending CF content. DMA results revealed that storage modulus and loss modulus values of composites increased with increasing CF content.     

Allyloxy-modified starch with low degree of substitution for fiber reinforced thermoset starch composites

In the present work dough moulding compound premixes of allyl glycidyl ether modified (AGE)-potato starch, (DS) = 0.2, has been prepared and tested for its fiber reinforced composite properties. The AGE-starch was hydrolyzed with α-amylase under neutral condition for 6 h at 45 °C for improved process ability. The grafting and hydrolytic scission was confirmed by nuclear magnetic resonance (NMR) and size exclusion chromatography (SEC), respectively. Homogeneous composite premixes of AGE-starch, wood fibers, various amount of glycerol and ethylene glycol dimethacrylate were successfully mixed with a Brabender-kneader at 55 °C and cured by compression molding at 150 °C using 2 wt% of dibenzoyl peroxide. Adding 5 wt% of glycerol did not reduce the ultimate strength of the composites; 10% glycerol reduced the strength from 60 MPa to 40 MPa, and 16% glycerol to 14 MPa. The results with 5 wt% glycerol are comparable with earlier achieved results. The water absorption rate increased with increased glycerol content and the mechanical strength of the composites was lost completely when the moisture uptake reached 15 wt%.     

Microstructure,flexural properties and durability of coir fibre reinforced concrete beams externally strengthened with flax FRP composites

This study investigated the flexural behaviour of plain concrete (PC) and coir fibre reinforced concrete (CFRC) beams externally strengthened by flax fabric reinforced epoxy polymer (FFRP) composites. PC and CFRC beams without and with FFRP (i.e. 2, 4 and 6 layers) reinforcement were tested under three- and four-point bending. The microstructures of coir fibre, coir/cement matrix, flax/epoxy matrix, and FFRP/concrete interfaces were analysed using scanning electronic microscope (SEM). Test results indicated that the peak load, flexural strength, deflection and fracture energy of both PC and CFRC specimens enhanced proportional to an increase of FFRP layers. Coir further increased load, strength and energy of the specimens remarkably. It was also found that the thickness and coir influenced the failure modes while the test method influenced the load and energy of the specimens remarkably. SEM studies showed effective bond at coir/cement, flax/epoxy and FFRP/concrete interfaces. Therefore, it concluded that natural FFRP composites can be used to repair or retrofit existing concrete structures.     

Reinforcement of ramie fibers on regenerated cellulose films

All-cellulose composite films reinforced with ramie fibers were prepared from aqueous NaOH–urea solvent system via a simple pathway. The structure and physical properties of the modified ramie fibers and composite films were characterized by scanning electron microscope (SEM), wide angle X-ray diffraction (WAXD), Fourier transform infrared spectrometer, ultraviolet–visible spectroscope, thermogravimetry, biodegradation tests and tensile tests. The results revealed that a good compatibility existed between the modified ramie fibers and cellulose matrix. The all-cellulose composite films exhibited high tensile strength, good optical transmittance, thermal stability, and biodegradability. The tensile strength and elastic modulus of the composite films increased with an increase of the ramie fibers. These high-strength biodegradable films prepared by a “green” pathway have potential applications as packaging materials and biomaterials.     

Polyoxymethylene composites with natural and cellulose fibres: Toughness and heat deflection temperature

Cellulose and abaca fibre reinforced polyoxymethylene (POM) composites were fabricated using an extrusion coating (double screw) compounding followed by injection moulding. The long cellulose or abaca fibres were dried online with an infrared dryer and impregnated fibre in matrix material by using a special extrusion die. The fibre loading in composites was 30 wt.%. The tensile properties, flexural properties, Charpy impact strength, falling weight impact strength, heat deflection temperature and dynamic mechanical properties were investigated for those composites. The fibre pull-outs, fibre matrix adhesion and cracks in composites were investigated by using scanning electron microscopy. It was observed that the tensile strength of composites was found to reduce by 18% for abaca fibre and increase by 90% for cellulose fibre in comparison to control POM. The flexural strength of composites was found to increase by 39% for abaca fibre and by 144% for cellulose fibre. Due to addition of abaca or cellulose fibre both modulus properties were found to increase 2-fold. The notched Charpy impact strength of cellulose fibre composites was 6-fold higher than that of control POM. The maximum impact resistance force was shorted out for cellulose fibre composites. The heat deflection temperature of abaca and cellulose fibre composites was observed to be 50 °C and 63 °C higher than for control POM respectively.     

Shape memory and thermo-mechanical properties of shape memory polymer/carbon fiber composites

In this study, chopped carbon fiber reinforced trans-1, 4-polyisoprene (TPI) was developed via a proposed new manufacturing process with the aim of improving weak mechanical properties of bulk TPI bulk. Specimens of the developed shape memory polymer (SMP) composites were fabricated with carbon fiber weight fraction of 5%, 7%, 9%, 11% and 13%, respectively. Measured are the effects of chopped carbon fiber and temperature on: (a) shape recovery ratio and rate; (b) stress–strain relationship; (c) maximum tensile stress, strain and Young’s modulus; and (d) maximum stress and residual strain under a constant strain cyclic loading. In addition, SEM micrographs were also presented to illustrate the fracture surface. The present experimental results show that the SMP with 7% carbon fiber weight fraction appears to perform best in all the tests. This indicates that the 7% carbon fiber weight fraction could be the optimum value for the SMP developed using the proposed manufacturing process.     

Influence of concrete matrix and type of fiber on the shear behavior of self-compacting fiber reinforced concrete beams

Steel fibers are known to improve shear behavior. The Design Codes (Eurocode 2 (EC2), Spanish EHE-08, Model Code 2010 and RILEM approach) have developed formulas to calculate the fiber contribution to shear, mainly focused on standard FRCs, i.e. medium strength concretes with a low content of normal strength steel fibers. However, in real applications other combinations are possible, such as high or medium strength concretes with high strength steel fibers of different lengths and geometry. An experimental program consisting of 12 self-compacting fiber reinforced concrete (SCFRC) I-type beams was carried out. All the beams had the same geometry and fiber content (50 kg/m³), and they were made with two different concrete compressive strength values and five different types of steel fibers and were tested for shear. The main conclusions reached were that the type of fiber substantially affects shear behavior, even when the Design Code formulas indicate similar contributions. The combination of high strength concrete matrixes with low strength fibers does not seem to be efficient. Also, the use of high residual flexural tensile strength values (e.g. f_R3 or f_R4) does not appear to be the most accurate reference value to calculate the beam shear strength in these cases. The present Design Codes consider standard FRCs, but their formulas should be revised for concretes with fibers of different strengths, slenderness and geometry, since these properties substantially affect shear behavior.     

Additive manufacturing of carbon fiber reinforced thermoplastic composites using fused deposition modeling

Additive manufacturing (AM) technologies have been successfully applied in various applications. Fused deposition modeling (FDM), one of the most popular AM techniques, is the most widely used method for fabricating thermoplastic parts those are mainly used as rapid prototypes for functional testing with advantages of low cost, minimal wastage, and ease of material change. Due to the intrinsically limited mechanical properties of pure thermoplastic materials, there is a critical need to improve mechanical properties for FDM-fabricated pure thermoplastic parts. One of the possible methods is adding reinforced materials (such as carbon fibers) into plastic materials to form thermoplastic matrix carbon fiber reinforced plastic (CFRP) composites those could be directly used in the actual application areas, such as aerospace, automotive, and wind energy. This paper is going to present FDM of thermoplastic matrix CFRP composites and test if adding carbon fiber (different content and length) can improve the mechanical properties of FDM-fabricated parts. The CFRP feedstock filaments were fabricated from plastic pellets and carbon fiber powders for FDM process. After FDM fabrication, effects on the tensile properties (including tensile strength, Young's modulus, toughness, yield strength, and ductility) and flexural properties (including flexural stress, flexural modulus, flexural toughness, and flexural yield strength) of specimens were experimentally investigated. In order to explore the parts fracture reasons during tensile and flexural tests, fracture interface of CFRP composite specimens after tensile testing and flexural testing was observed and analyzed using SEM micrograph.     

Fluorinated graphene reinforced polyimide films with the improved thermal and mechanical properties

In order to explore the addition effect of fluorinated graphene (FG) on the mechanical and thermal performances of polyimide (PI) matrix, FG sheets are first prepared and employed as the nanofillers to construct PI/FG nanocomposite films. The prepared film is optically transparent at low content of FG and experimental results demonstrate that the addition of FG can effectively enhance the properties of PI matrix. Especially, compared with pure PI matrix, the addition of 0.5 wt% FG in PI can endow 30.4% increase in tensile stress and 115.2% increase in elongation at break. Experimental analyses considering the morphology and microstructure are also conducted, and the results indicate that the improved mechanical properties of the PI/FG nanocomposite films are mainly attributed to the good dispersibility of FG sheets in PI host, and the effective stress transfer between the polymer and the FG.