Effects of processing conditions on the mechanical and water absorption properties of resin transfer moulded kenaf fibre reinforced polyester composite laminates

This paper focuses on the mechanical and water absorption properties of kenaf fibre reinforced polyester laminates manufactured by resin transfer moulding. Varying processing conditions were considered as alternatives to fibre treatments, thereby potentially avoiding additional cost and complexity in the manufacturing process. Laminates were produced by altering fibre moisture content, mould temperature and mould pressure following injection. Tensile, flexural, impact and water absorption tests were conducted. Processing conditions were found to have little effect on properties except for pressurisation which increased tensile and flexural strength and decreased water absorption at low fibre volume fractions. Examinations using a scanning electron microscope showed that all the laminates failed by fibre pull-out.     

Development of kenaf-glass reinforced unsaturated polyester hybrid composite for structural applications

The main aim of this paper is to develop kenaf-glass (KG) fibres reinforced unsaturated polyester hybrid composite on a source of green composite using sheet moulding compound process. Unsaturated polyester resin (UPE) and KG fibres in mat form were used at a ratio of 70:30 (by volume) with treated and untreated kenaf fibre. The kenaf fibre was treated with 6% sodium hydroxide (NaOH) diluted solution for 3 h using mercerization method. The hybrid composites were tested for flexural, tensile and Izod impact strength using ASTM D790-03, ASTM D618 and ASTM D256-04 standards respectively. The highest flexural, tensile and impact strength were obtained from treated kenaf with 15/15 v/v KG fibres reinforced UPE hybrid composite in this investigation.Scanning electron microscopy fractography showed fibre cracking, debonding and fibre pulled-out as the main fracture mode of composites and kenaf treated 15/15 v/v KG reinforced hybrid composite exhibited better interfacial bonding between the matrix and reinforcement compared to other combinations.     

Fabrication and testing of natural fibre composites: Vakka, sisal, bamboo and banana

A study has been carried out to investigate the tensile, flexural and dielectric properties of composites made by reinforcing vakka as a new natural fibre into a polyester resin matrix. The fibres extracted by retting and manual processes have been used to fabricate the composites. These composites are tested for tensile, flexural and dielectric properties and compared with those of established composites like sisal, bamboo and banana made under the same laboratory conditions. The composites are fabricated up to a maximum volume fraction of fibre of 0.37 in the case of tensile testing, and 0.39 for flexural and dielectric testing. It has been observed that the tensile properties increase with respect to volume fraction of fibre for vakka fibre composite and are also more than those of sisal and banana composites and comparable to those of bamboo composites. The flexural strength of vakka fibre composite is more than that of banana composite and is closer to sisal fibre composite with respect to the volume fraction of fibre, where as the flexural modulus is much higher than those of banana and sisal fibre composites and also very much closer to bamboo fibre composites. The dielectric strength of vakka fibre composite increases with increase in volume fraction of fibre in the composite unlike the case of sisal, bamboo and banana composites. The dielectric strength being a unique feature of vakka fibre composite, can be suggested for electrical insulation applications.     

静电植绒法处理多壁碳纳米管改性玻纤织物/环氧树脂复合材料的制备及力学性能

为提高玻纤增强环氧树脂复合材料的力学性能,采用静电植绒法将多壁碳纳米管(MWCNTs)附着在玻纤织物表面,得到改性的玻纤织物。利用一种低黏度的环氧树脂和所制得的改性织物,采用真空辅助成型工艺(VARI)制备了MWCNTs改性格玻纤织物/环氧树脂复合材料层合板,表征了层合板的力学性能。对进行力学实验后的MWCNTs改性玻纤织物/环氧树脂复合材料试样断口进行了SEM和OPM观察。结果显示:与未添加MWCNTs的玻纤织物/环氧树脂复合材料层合板相比,添加了MWCNTs的层合板的拉伸强度降低了10.24%,弯曲强度降低了13.90%,压缩强度降低了17.33%,拉伸模量和弯曲模量分别提高了19.38%和16.04%,压缩模量提高了13%;MWCNTs与玻纤织物之间的结合较弱,在拉伸作用下,存在明显的脱粘和分层;将改性玻纤织物在200℃下热压处理2h后,制备的MWCNTs改性玻纤织物/环氧树脂复合材料层合板的力学性能均有所提高,热压处理后树脂与玻纤织物之间的界面结合得到改善。     

Bisphenol A based polyester binder as an effective interlaminar toughener

Bisphenol A based thermoplastic polyesters are commonly used in the industry as binders, or tackifiers, to produce cost-saving preforms in Liquid Composite Moulding processes such as Vacuum Assisted Resin Transfer Moulding (VARTM). However, it is often reported that the presence of these polyesters has a detrimental effect on the mechanical properties of the resulting composite laminates. In contrast, this study shows that interlaminar toughness can be increased without negatively affecting other properties by coating the reinforcing plies with a bisphenol A based thermoplastic polyester if some precautions are taken in mind.The polyester was added to an epoxy resin in order to study its effect on the thermophysical properties and fracture toughness of the bulk epoxy. The polyester molecules acted as a plasticizer for the epoxy resin when the polyester was added in low amounts. This increased the bulk fracture toughness of the epoxy resin by 30%. Polyester modified glass/epoxy laminates were produced and tested for Mode I interlaminar fracture toughness and flexural properties. The increased toughness of the epoxy matrix led to a 60% increased Mode I interlaminar fracture toughness of the laminates, without negatively affecting flexural stiffness and strength of the laminates.     

Influence of moisture absorption on flexural properties of syntactic foams

This work studies the influence of moisture absorption on the flexural properties of vinyl ester matrix–glass particle syntactic foams. The extent and the effect of moisture absorption are related to the wall thickness and volume fraction of the particles present in the composite. Four compositions of vinyl ester–glass systems are exposed to deionized and sea water conditions. Experimental findings are compared with results on virgin specimens. In general, the exposure of syntactic foams to a water environment yields a deterioration of Young’s modulus. This phenomenon is more prominent with deionized water as compared to sea water and increases with the particle volume fraction. In addition, results from water absorption tests show that syntactic foams have a lower diffusivity as compared to the neat resin. Experimental data are interpreted by using available modeling tools that allow for predicting the composite behavior from the properties of its constituents.     

Mechanical properties of natural fibre reinforced polyester composites: Jowar,sisal and bamboo

In this paper, the experiments of tensile and flexural tests were carried out on composites made by reinforcing jowar as a new natural fibre into polyester resin matrix. The samples were prepared up to a maximum volume fraction of approximately 0.40 from the fibres extracted by retting and manual process, and compared with established composites like sisal and bamboo developed under similar laboratory conditions. Jowar fibre has a tensile strength of 302 MPa, modulus of 6.99 GPa and an effective density of 922 kg/m³. It was observed that the tensile strength of jowar fibre composite is almost equal to that of bamboo composite, 1.89 times to that of sisal composite and the tensile modulus is 11% and 45% greater than those of bamboo and sisal composites, respectively at 0.40 volume fraction of fibre. The flexural strength of jowar composite is 4%, 35% and the flexural modulus is 1.12 times, 2.16 times greater than those of bamboo and sisal composites, respectively. The results of this study indicate that using jowar fibres as reinforcement in polyester matrix could successfully develop a composite material in terms of high strength and rigidity for light weight applications compared to conventional sisal and bamboo composites.     

Comparison of tensile and compressive characteristics of vinyl ester/glass microballoon syntactic foams

The present study is focused on the synthesis and characterization of vinyl ester/glass microballoon syntactic foams. Tensile and compressive properties of vinyl ester matrix syntactic foams are characterized. Results show that the compressive strength and moduli of several syntactic foam compositions are comparable to those of the neat matrix resin. Due to the lower density of syntactic foams, the specific compressive properties of all compositions are higher than those of the neat resin. Similar trends are observed in the tensile properties. Mechanical properties of vinyl ester matrix syntactic foams are compared to well-documented mechanical properties of epoxy matrix systems. The comparison shows that low cost vinyl ester resins, which are extensively used in marine applications, can result in syntactic foams with comparable performance to epoxy matrix systems. In addition, tensile modulus is found to be 15–30% higher than the compressive modulus for all syntactic foam compositions. This difference is related to the possibility of particle fracture in the stress range where modulus is calculated in the compressive stress–strain curves.     

Effect of water immersion on the interlaminar and flexural performance of low cost liquid resin infused carbon fabric composites

This study investigates some potential benefits of using non-epoxy matrices in carbon fibre composites, targeting specific marine and wind energy applications. Water uptake during and after immersion for up to 28 days in deionised water at 40 °C, and the effects of such conditioning on the interlaminar shear and flexural performance of the composites with isophthalic polyester, vinyl ester and urethane acrylate matrices were compared to those of equivalent composites impregnated with three grades of epoxy resin. Results demonstrated that, although the epoxy systems perform equally or better than the alternative resins in the dry state, they are also more sensitive to property degradation due to water ingress. The relatively lower water absorption and subsequent limited reduction in performance of vinyl ester and urethane acrylate composites is sufficiently promising to justify further study.     

单向碳纤维增强树脂基复合材料的超低温力学性能

采用真空袋-热压罐工艺制备单向碳纤维增强树脂基复合材料(CFs/EP)层合板,并将高低温试验箱与万能试验机相结合,通过合理使用低温胶和低温引伸计,并在降温过程中实施应力-应变实时调零等关键技术,在室温和液氧超低温度(-183℃)下对单向CFs/EP层合板进行拉伸和弯曲试验,研究了其超低温力学性能,并根据室温和超低温试验后试样的微观和宏观特征,揭示了超低温环境下复合材料力学性能变化机制。结果表明,与室温力学性能相比,单向CFs/EP层合板超低温拉伸强度下降约为9.5%,而拉伸模量上升约为6.2%,主要是由于超低温环境下,树脂的收缩使绝大部分碳纤维与树脂间形成了强界面,拉伸后试样呈"劈裂式"破坏形式,无法使每根纤维都充分发挥其强度,拉伸强度下降,同时超低温也限制了树脂大分子链的运动,所以导致单向CFs/EP层合板拉伸模量上升;单向CFs/EP层合板超低温弯曲强度和弯曲模量分别提高约54.75%和11.64%,这是由于单向CFs/EP层合板的常温和超低温的弯曲破坏形式均为分层剪切破坏,超低温下复合材料的界面增强,提高了单向CFs/EP层合板抵抗剪切分层的能力,进而使CFs/EP的弯曲性能得到提高。     

Investigation on mechanical properties of woven alovera/sisal/kenaf fibres and their hybrid composites

The go-green concept results in multipoint focus towards materials made from nature; easily decomposable and recyclable polymeric materials and their composites along with natural fibres ignited the manufacturing sectors to go for higher altitudes in engineering industries. This is due to the health hazard and environmental problems faced in manufacturing and disposal of synthetic fibres. This study was undertaken to analyse the suitability of new natural fibre as an alternative reinforcement for composite materials. In this paper, tensile, flexural and impact test is made for the woven alovera and kenaf (AK), sisal and kenaf (SK), alovera, sisal and kenaf fibre hybrid epoxy composites (ASK). The composite laminates are made through a hand-layup process. The surface analysis is studied through scanning electron microscopy. From the investigation the SK hybrid composite shows good tensile property, AK hybrid composite shows better flexural property and the best impact strength is observed for ASK hybrid composite. The natural fibres slowly replace the synthetic fibres from its environmental impact, marching towards a revolution in engineering materials.     

PEK-C膜层间增韧碳纤维/环氧树脂复合材料的力学性能

为探究热塑性酚酞基聚醚酮（Polyaryletherketone with Cardo,PEK-C）树脂薄膜及膜厚对层间增韧碳纤维/环氧树脂复合材料力学性能的影响,利用浸渍提拉法制备了三种不同厚度（分别约为1 μm、10 μm、30 μm）的PEK-C膜,通过热压成型制备了层间增韧碳纤维/环氧树脂复合材料层合板,对其进行了Ⅰ型层间断裂韧性、冲击后压缩强度、层间剪切及弯曲性能测试,并利用SEM观察微观形貌及AFM扫描微观相图。结果表明:不同PEK-C膜厚增韧碳纤维/环氧树脂复合材料的Ⅰ型层间断裂韧性、冲击后压缩强度及层间剪切强度有不同程度提高,Ⅰ型层间断裂韧性及层间剪切强度以膜厚为10 μm最佳,分别增大了157.17%和17.57%,冲击后压缩强度以膜厚为30 μm最佳,达到了186.67 MPa,这是由于PEK-C与环氧树脂在热压固化过程中形成了双相结构,改善了材料韧性;但弯曲性能持续下降,强度及模量由未增韧的1 551 MPa、106 GPa分别降至30 μm时的965 MPa、79 GPa,这是由于PEK-C树脂扩散进入环氧树脂中,降低了纤维体积分数及材料刚度。      

Vacuum-assisted resin infusion (VARI) and hot pressing for CaCO3 nanoparticle treated kenaf fiber reinforced composites

This work was to apply the vacuum-assisted resin infusion (VARI) process and use calcium carbonate inorganic nanoparticle impregnation (INI) to improve the mechanical properties and water resistance of the kenaf fiber/polyester composites. The results show that the modulus of elasticity (MOE), modulus of rapture (MOR), tensile modulus (TE) and tensile strength (TS) of the composites made with INI-treated fibers are increased by 33.1%, 64.3%, 22.3% and 67.8%, respectively, compared with the composites made with un-treated fibers. The thickness swelling of 24-h water submersion is reduced from 19.7% to 1.9%. The moisture contents of the composites after the conditioning and water submersion are reduced from 5.8% to 1.5% and 18.3% to 2.2%, respectively, when INI-treated fibers are employed. The improvement makes the kenaf fiber/polyester composites possible to replace the glass fiber SMC for the automobile application.     

Development and Characterization of the Midrib of Coconut Palm Leaf Reinforced Polyester Composite

In this paper, midrib of coconut palm leaves (MCL) was investigated for the purpose of development of natural fiber reinforced polymer matrix composites. A new natural fiber composite as MCL/polyester is developed by the hand lay-up method, and the material and mechanical properties of the fiber, matrix and composite materials were evaluated. The effect of fiber content on the tensile, flexural, impact, compressive strength and heat distortion temperature (HDT) was investigated. It was found that the MCL fiber had the maximum tensile strength, tensile modulus flexural strength, flexural modulus and Izod impact strength of 177.5MPa, 14.85GPa, 316.04MPa and 23.54GPa, 8.23KJ/m² respectively. Reinforcement of MCL enhanced the mechanical properties of pure polyester, including that of tensile strength (by 26%), tensile modulus (by 356%), flexural strength (by 41.81%), flexural modulus (by 169%) and Izod impact strength (by 23 times), but the compressive strength was adversely affected. HDT decreased due to fiber loading, but increased with weight fraction of fiber content. Moreover, the experimental results were compared with theoretical model (Rule of mixture) and other natural fiber /polyester composites.     

Nano-enhanced composite materials under thermal shock and environmental degradation: A durability study

Carbon nanotubes (CNTs) were incorporated at 0.5 wt% in epoxy resin using sonication at two different levels of amplitude (50% and 100% of 400 W nominal sonication power). The CNTs modified epoxy systems were used to manufacture carbon fibre reinforced laminates (CFRPs). All specimens were subjected to thermal shock and hygrothermal exposure. The presence of CNTs did not alter the water absorption profiles for the epoxy resin, but it resulted in a spectacular 40% reduction in the water uptake at equilibrium for the CFRPs. The interlaminar shear strength of the CFRPs was not significantly affected by the thermal shock cycles; however it was reduced by 50–60% after hygrothermal exposure. The addition of CNTs led to slightly lower interlaminar shear strength values in the as-manufactured state. However their presence did not accelerate the deterioration of the strength after the environmental exposure. Although the addition of CNTs did not significantly influence the thermomechanical properties of the resin, they were beneficial in the case of the CFRPs since (i) they enhanced the storage modulus and glass transition temperature and (ii) limited the deterioration of these properties after thermal shock and hygrothermal exposure. The amplitude level during sonication which determined the dispersion state and length of the CNTs had a clear effect on the durability of the studied systems.     

Flexural properties of z-pinned laminates

This paper examines the effect of pinning on the flexural properties, fatigue life and failure mechanisms of carbon/epoxy laminates. Five-harness satin weave carbon/epoxy laminates were reinforced in the through-thickness direction with different volume fractions and sizes of fibrous composite pins. Microscopic examination of the laminates before flexural testing revealed that the pins caused considerable damage to the microstructure, including out-of-plane crimping, in-plane distortion and breakage of the fibres and the formation of resin-rich zones around each pin. The pins also caused swelling of the laminate that reduced the fibre volume content. Despite the damage, the pins did not affect the flexural modulus of the laminate. However, increasing the volume content or diameter of the pins caused a steady decline in the flexural strength and fatigue life, which appear to be governed by fiber rupture on the tensile side of the laminate. Property changes are discussed in terms of transitions in the dominant failure mechanisms due to the presence of pins.     

Effect of moisture on elastic and viscoelastic properties of epoxy and epoxy-based carbon fibre reinforced plastic filled with multiwall carbon nanotubes

In this study, we investigated the peculiarities of moisture absorption and moisture-induced effects on the elastic and viscoelastic flexural properties of epoxy resin and carbon fibre reinforced plastic (CFRP) filled with multiwall carbon nanotubes (MWCNTs). Short-term cyclic creep-recovery tests of moistened epoxy and CFRP filled with MWCNTs revealed improvements in creep resistance for both materials. The addition of MWCNTs to the epoxy resin suppressed the moisture absorption by the material, causing a reduction in the diffusion coefficient by 31% and equilibrium moisture content by 15%. The addition of MWCNTs reduced the flexural strength of moistened epoxy and CFRP samples by approximately half, and also lowered the flexural modulus by ∼1.4 and ∼3 times, elastic strain by 1.25 and 1.04 times, viscoelastic strain by 1.39 and 1.03 times, and plastic strain by 2.68 and 1.60 times, respectively.     

The effect of low energy impact on the tensile strength of coated and uncoated glass particulate composites

The residual tensile strength of glass filled particulate composites has been determined after low energy impact for various energy values. The material systems constructed for the needs of this research consisted of epoxy resin filled with glass beads. The glass beads were either uncoated or alternatively coated with a reactive silane based bonding agent. Specimens with various filler volume fractions were available. The effect of silane coating as well as the filler volume fraction was analytically discussed. Finally, a model developed in previous work for continuous fibre reinforced composite laminates was adopted to describe the residual tensile strength after impact. In most of the cases the predicted curves fit the experimental results very well.     

Optimization of mechanical properties of non-woven short sisal fibre-reinforced vinyl ester composite using factorial design and GA method

This work presents a systematic approach to evaluate and study the effect of process parameters on tensile, flexural and impact strength of untreated short sisal fibre-reinforced vinyl ester polymer-based composites and predicts the optimum properties of random natural fibre-reinforced composites. The natural fibre of sisal at lengths of 10, 30 and 50 mm and vinyl ester resin at loadings of 15, 30 and 45 (wt%) were prepared. The composite panel was then fabricated using hand lay method in cold process of size 180×160 mm². Samples were then cut from the panel and subjected to mechanical properties testing such as tensile, flexural and impact strengths. The average tensile strength ranges between 27·1 and 43·9 MPa. The flexural strength ranged between 26·9 and 49·5 MPa and the impact strength ranged between 16 and 93 J/m. The strength values were optimized using factorial design and genetic algorithm (GA) method. The predicted optimum process parameter values are in good agreement with the experimental results.     

Excellent flexural properties of aminimide-cured epoxy resin as a matrix for mica-dispersed polymer composites

The flexural behaviour of mica-dispersed epoxy resin composites has been examined. The flexural strength and flexural modulus have been determined as a function of the volume fraction of mica flakes (V _f) for both aminimide-cured epoxy resin matrix and a conventional epoxy resin reference matrix. On the basis of microscopic observation of fractured surfaces, the effect of improving the particle-matrix interface has been analysed using the modulus reduction factor (MRF) in a modified form. It is found that there is a steady increase in the flexural modulus with the volume fraction of mica flake for the aminimide-cured epoxy resin matrix. In contrast, the increase in flexural modulus levels off at a high content of filler for the reference samples. It is noteworthy that the intact mica flakes without surface treatment exhibit a substantial reinforcing effect on the flexural strength in the case of aminimide-cured epoxy resin composites. A further surprise is the difference among the curing agents used. The reference epoxy resins behave just like conventional matrix resins, exhibiting 30 to 40% reduction in the flexural strength when a small fraction of mica is added. These superior properties of the matrix resin for the composites are ascribed to the characteristics of aminimide-cured epoxy resins such as hardness, toughness, and excellent adhesivity.