All-polyamide composites prepared by resin transfer molding

Resin transfer molding (RTM) was used to manufacture all-polyamide (all-PA) composites in which PA6 matrix was in situ formed by the anionic polymerization of ε-caprolactam (CL). Influence of molding temperature (T _M), a critical process parameter, on the structure and properties of all-PA composites was investigated using TGA, DSC, SEM, and tensile, flexural test. Increasing T _M resulted in the decrease of CL conversion and the enhancement of fiber/matrix interface bonding. By comparing the mechanical properties of all-PA composites prepared at different T _M (140–200 °C), an optimal T _M (180 °C) was found in this temperature range. As a whole, the complete consolidation of all-PA composites and the remarkable reinforcing effect of PA66 fibers on PA6 matrix were assured by low-void fraction, high-CL conversion and strong interface performance though in a wide T _M range.     

Electrical properties of short sisal fiber reinforced polyester composites fabricated by resin transfer molding

The electrical properties of sisal fiber reinforced polyester composites fabricated by resin transfer molding (RTM) have been studied with special reference to fiber loading, frequency and temperature. The dielectric constant (ε′), loss factor (ε″), dissipation factor (tan δ) and conductivity increases with fiber content for the entire range of frequencies. The values are high for the composites having fiber content of 50 vol.%. This increment is high at low frequencies, low at medium frequencies, and very small at high frequencies. The volume resistivity varies with fiber loading at lower frequency and merges together at higher frequency. When temperature increases the dielectric constant values increases followed by a decrease after the glass transition temperature. This variation depends upon the fiber content. Finally an attempt is made to correlate the experimental value of the dielectric constant with theoretical predictions.     

Post-fire flexural properties of fibre-reinforced polyester, epoxy and phenolic composites

The effect of fire damage on the flexural properties of fibre-reinforced polymer (FRP) composites is investigated. The FRP composites studied contained glass, carbon or Kevlar fibres with a polyester, epoxy or phenolic resin matrix. Artificial fire tests were performed on the composites using a cone calorimeter. The residual flexural modulus and strength of the burnt composites were determined at room temperature after the fire tests. The post-fire flexural properties of all the composites decreased rapidly with increasing heating time. Even the properties of the fibre-reinforced phenolic materials were severely degraded despite their low flammability and excellent fire resistance. The flexural properties of the phenolic-based composites were reduced due to thermal degradation and cracking of the resin matrix. In comparison, the properties of the polyester- and epoxy-based composites were reduced by combustion of the resin and formation of delamination cracks. A model is presented for determining the post-fire flexural properties of FRP composites with good accuracy.     

A comparative study on mechanical properties of carbon fiber/PEEK composites

The aim of this work was to improve mechanical properties such as flexural strength and interlaminar shear strength (ILSS) of polyetheretherketone (PEEK) thermoplastic polymer which has very high processing temperature due to its high melting temperature. Carbon fiber (CF) surface was modified by two different methods: oxidative and non-oxidative. Piranha solution and chromate solution were used for chemical treatment (oxidative treatment), and silicone based polymers were used for polymer coating (non-oxidative). The changes on the surface structure and surface chemistry were characterized by scanning electron microscopy and Fourier transform infrared spectroscopy (FTIR), respectively. FTIR results indicate that coating fibers decreases carbon element content, whereas increases the oxygen and silicone content as well as their functional groups on the surface. Flexural strength and ILSS properties of CF/PEEK composites were measured according to ASTM D-790 and ASTM D2344, respectively.     

天然细菌纤维素增强不饱和聚酯树脂复合材料的制备及性能

将天然纤维-细菌纤维素（BC）作为增强材料加入不饱和聚酯树脂（UPR）基体中,采用RTM工艺制备BC/UPR复合材料,并对其力学性能、吸湿性能进行了研究。通过紫外辐照方法探讨了BC/UPR复合材料的降解性能。研究结果表明:通过对细菌纤维素的表面改性,在亲水性的天然纤维和疏水性的高聚物基体之间形成了化学键结合,提高了BC/UPR复合材料的力学性能;BC纤维体积分数的增加也有助于提高力学性能, 当纤维体积分数为20%时,该复合材料拉伸强度最高可达152.9MPa; BC/UPR复合材料的吸湿过程符合Fick定律,吸湿可导致力学性能下降; BC/UPR复合材料吸收光能后,表面含氧官能团数量增加,发生一定程度的光降解。      

MgO／不饱和聚酯树脂复合材料的制备与性能

利用对苯二甲酸二甲酯（DMT）、顺丁烯二酸酐（MA）和1,2-丙二醇（PG）制备对苯型不饱和聚酯树脂（UPR）,然后与表面改性后的MgO粉体机械共混制备了MgO／UPR复合材料,考察改性后MgO粉体在UPR基体中的分散情况及其对MgO／UPR复合材料动态热力学性能、耐热性及硬度的影响。XRD、FTIR和SEM测试结果表...     

Effect of fiber surface modification on the mechanical and water absorption characteristics of sisal/polyester composites fabricated by resin transfer molding

Sisal fibers were subjected to various chemical and physical modifications such as mercerization, heating at 100 °C, permanganate treatment, benzoylation and silanization to improve the interfacial bonding with matrix. Composites were prepared by these fibers as reinforcement, using resin transfer molding (RTM). The mechanical properties such as tensile, flexural and impact strength were examined. Mercerized fiber-reinforced composites showed 36% of increase in tensile strength and 53% in Young’s modulus while the permanganate treated fiber-reinforced composites performed 25% increase in flexural strength. However, in the case of impact strength, the treatment has been found to cause a reduction. The water absorption study of these composites at different temperature revealed that it is less for the treated fiber-reinforced composites at all temperatures compared to the untreated one. SEM studies have been used to complement the results emanated from the evaluation of mechanical properties.     

Low-cost tooling for the hot press moulding of glass fibre-reinforced polyester: a case study

Glass fibre-reinforced polyester, with its high strength to weight ratio, offers great potential as a structural material for use in the civil engineering industry. One application in which it has shown particular promise is in the form of repeatable basic units that can be assembled together to form a structure. This paper describes the manufacture of a moulding tool to enable a limited number of glass fibre-reinforced polyester components to be manufactured economically by the hot press moulding of sheet moulding compound. It outlines the manufacture of the tool and the difficulties encountered at all stages in the production of the final article. The paper also illustrates a structural model to one-fifth scale which has been fabricated from the final composite sheet moulding compound units and which will be tested to destruction. The results of this test and those for small tensile coupons will be the subject of a further paper.     

Improving the resin transfer moulding process for fabric-reinforced composites by modification of the fabric architecture

The use of resin transfer moulding (RTM) as an economic and efficient means of producing high-performance fibre-reinforced composites is critically limited by the permeability of the fabrics employed. Commercial fabrics are available where the architecture of the reinforcement is designed to cluster the fibres giving higher permeabilities than conventional fabrics. This has been shown to improve processing times, but there is evidence that such clustering is detrimental to the mechanical performance of the resulting composite material.

The objective of this work was to relate variations in permeability, and in the laminate mechanical properties, to differences in microstructure. A series of experimental carbon fibre fabrics woven to incorporate a novel flow enhancement concept (use of 3K tows in a 6K fabric) were used to manufacture plates by RTM in a transparent mould. The progress of the resin front was recorded to computer disc during injection, thus allowing the permeabilities of the fabrics to be calculated.

The manufactured plates were subsequently sectioned for mechanical testing (moduli and strengths in tension and compression) and automated image analysis. Relationships were sought between measured permeabilities, mechanical properties and microstructures using a Quantimet 570 automatic image analyser to determine fractal dimensions from polished sections. It has been shown that variations in the microstructures can be related to the permeability and mechanical property values obtained. Further the deterioration of mechanical properties for the novel fabrics with reduced fibre volume fractions is less than has been reported for fabrics with clustered flow-enhancing tows at constant fibre volume fraction.     

The effects of moulding geometry on the structure and mechanical properties of fibre-reinforced polypropylene structural foam mouldings

The influence of weld lines and changes in moulding section thickness on structure and mechnanical properties has been determined for short glass-fibre reinforced polypropylene structural foam prepared using a short-shot moulding procedure at two different melt injection times. Results are discussed in terms of the variability in skin to core thickness ratio, moulding density and fibre orientation obtained in these mouldings and subsequent effects on flexural stiffness and impact energy to failure.     

Effects of fibre surface silanisation on silica fibre/phenolics composites produced by resin transfer moulding process

Abstract

The effects of fibre surface silanisation on silica fibre/phenolics composites produced by the resin transfer moulding (RTM) solution impregnation route were investigated. Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and micro-Wilhelmy method were used to evaluate the surface properties of silanised silica fibre. The interlaminar shear strength (ILSS) measurements and morphological observations of the silica fibre/phenolics composites were also performed. The interactions occurring between silica fibre and the components of phenolic resin solution affect the dynamic adsorption behaviour of phenolic resin onto fibre reinforcement. The competitive adsorption of ethanol as solvent onto silica fibre suppresses that of phenolic resin. Fibre surface silanisation by γ-aminopropyl-triethoxysilane (γ-APS), γ-glycidoxypropyl-trimethoxysilane (γ-GPS) and γ-methacryloxypropyl-trimethoxysilane (γ-MPS) leads to the improvement of mechanical interfacial properties of silica fibre/phenolics composites on one hand and decreases the inhomogeneities of resin distribution and mechanical interfacial properties at different regions of the RTM product on the other hand.     

The effect of resin failure strain on the tensile properties of glass fibre-reinforced polyester cross-ply laminates

An investigation has been made of the effect of resin properties on the transverse cracking behaviour of glass fibre-reinforced polyester resin three-ply laminates. The polyester resin properties were modified by the addition of a flexibilizing resin to produce five resin systems with failure stresses ranging from 1.75 to 11.1%. The mechanical properties of the resins which were determined, are observed to affect the stress level at which transverse cracking is initiated and the nature of the cracking behaviour. If fibre bunching is taken into account the Kies strain magnification theory can predict the general trend of the results. However, it is concluded that strain-rate effects associated with fibre bunching are worthy of further investigation.     

Environmental resistance of flax/bio-based epoxy and flax/polyurethane composites manufactured by resin transfer moulding

As biocomposites are highly sensitive to water absorption, the aim of this study was to compare the physical properties two biocomposites: (1) a flax/bio-based epoxy (Entropy SUPER SAP CLR/INS) and (2) a flax/polyurethane (HENKEL LOCTITE MAX 3). Both materials were reinforced with 14 layers of flax (TEXONIC twill 2 × 2) and manufactured using a resin transfer moulding process. Post-cured composite samples were aged at 90% RH and 30 °C for various periods of time up to 720 h. The results showed that both composites followed a Fickian diffusion behaviour. Water had a plasticizing effect on the composites and it changed their failure mode. This effect took longer to appear for the polyurethane composites. The chemical bonds between the hydroxyl groups of the fibres and the isocyanate lead to a stronger interface which improved the mechanical properties (short beam and compressive strengths) as compared to the flax/bio-epoxy composites.     

Some mechanical properties of untreated jute fabric-reinforced polyester composites

This research work is concerned with the evaluation of the mechanical properties—modulus, Poisson's ratio and strength—of woven jute fabric-reinforced composites. The specimens are prepared using hand lay-up techniques as per the ASTM standard. This is the first report by any single group of researchers in which tensile strength, compressive strength, flexural strength, impact strength, inplane shear strength, interlaminar shear strength and hardness are given. This work being an experimental study on untreated (`as received' jute fabric) woven jute fabric-reinforced polyester composites, demonstrates the potential of this renewable source of natural fibre for use in a number of consumable goods.     

Study on microstructures and mechanical properties of short-carbon-fiber-reinforced SiC composites prepared by hot-pressing

Short-carbon-fiber-reinforced silicon carbide composites were prepared by hot-pressing with SiC powder, Polycarbosilane as precursor polymer and MgO–Al₂O₃–Y₂O₃ as sintering additives. The phase composition, microstructure and mechanical properties of the composites with different Polycarbosilane content were investigated. The results showed that, dense composites could be prepared at a relatively low temperature of 1800 °C via the liquid-phase-sintering mechanism and the highest mechanical property was obtained for the composites with 20 wt.% PCS and 8 wt.% sintering additives. The amorphous interphase formed during sintering process in the composites not only contributed to the densification of the composites, but also improved the fiber–matrix bonding. The nano-silicon carbide derived from Polycarbosilane, could also play a role of improving the relative density of the composites.     

Thermal and dynamic mechanical properties of IPNS formed from unsaturated polyester resin and epoxy polyester

The interpenetrating polymer networks (IPNs) were formed by unsaturated polyester resin (UPR) polymerized by free radical initiators: benzoyl peroxide (BPO) or cumene hydroperoxide (CHP) and epoxy polyester (EP), cured with acid anhydrides: tetrahydrophthalic anhydride (THPA) or maleic anhydride (MA). IPNs consisting 10, 30, 50, 70, 90 wt% of EP were prepared. The effect of the EP component in the IPNs and the type of curing agent on the cure behavior, thermal, and viscoelastic properties have been investigated. The results showed that both EP content and used curing system influenced on studied properties. As the EP content increased, the glass transition temperatures (T _g) also increased. Moreover, higher values of tanδ_max and lower values of cross-linking density in a rubbery state (ν_e) of IPNs containing higher EP content, probably due to plasticization effect of EP component were observed. Additionally, more heterogeneous network structure (higher values of the full-width at half-maximum (FWHM) as the EP content decreased was prepared. The thermal and viscoelastic properties of the blends cured with BPO/MA or CHP/MA system were considerably better than those cured with BPO/THPA or CHP/THPA. The higher stiffness, ν_e, T _g and lower tanδ_max values were obtained. It was probably connected with the interactions of carbon–carbon double bonds of MA with vinyl monomer (styrene), UPR and radical initiators causing to obtain more cross-linked polymer network structure. This supposition was confirmed on basis of the cure reaction monitored by DSC. The chemical interactions between two components of the blends and epoxy hardener caused that the BPO/MA or CHP/MA cure systems influenced on the cure behavior of UPR and EP components in the IPNs. The exotherm peak temperature (T _max1) shifted to lower values compared to these in the neat UPR whilst T _max2 shifted to higher values than in the neat EP. However, the cure behavior of the UPR was not greatly affected by the presence of EP component when BPO/THPA or CHP/THPA cure systems were used due to the lack of chemical interactions between the components and their curatives.     

A review of the effect of stitching on the in-plane mechanical properties of fibre-reinforced polymer composites

This paper reviews over fifty studies into the effect of through-the-thickness stitching on the in-plane mechanical properties of fibre-reinforced polymer composites. Reviewed are the in-plane tensile, compressive, flexure, interlaminar shear, creep, fracture and fatigue properties, although little work has been undertaken on the last three properties. When comparing studies it is apparent that many contradictions exist: some studies reveal that stitching does not affect or may improve slightly the in-plane properties while others find that the properties are degraded. In reviewing these studies it is demonstrated that predicting the influence of stitching on the in-plane properties is difficult because it is governed by a variety of factors, including the type of composite (eg. type of fibre, resin, lay-up configuration), the stitching conditions (eg. type of thread, stitch pattern, stitch density, stitch tension, thread diameter), and the loading condition. The implications of these findings for the use of stitching in lightweight engineering structures are discussed.     

Comparison of the mechanical and physical properties of a carbon fibre epoxy composite manufactured by resin transfer moulding using conventional and microwave heating

Microwave processing holds great potential for improving current composite manufacturing techniques, substantially reducing cure cycle times, energy requirements and operational costs. In this paper, microwave heating was incorporated into the resin transfer moulding technique. Through the use of microwave heating, a 50% cure cycle time reduction was achieved. The mechanical and physical properties of the produced carbon fibre/epoxy composites were compared to those manufactured by conventional resin transfer moulding. Mechanical testing showed similar values of flexural moduli and flexural strength for the two types of composites after normalisation of the corresponding data to a common fibre volume fraction. A 9% increase of the interlaminar shear strength (ILSS) was observed for the microwave cured composites. This enhancement in ILSS is attributed to a lowering of resin viscosity in the initial stage of the curing process, which was also confirmed via scanning electron microscopy by means of improved fibre wetting and less fibre pull-out. Furthermore, both types of composites yielded minimal void content (<2%). Dynamic mechanical thermal analysis revealed comparable glass transition temperatures for composites produced by both methods. A 15 °C shift in the position of the β-transition peak was observed between thermally and microwave cured composites, suggesting an alteration in the cross-linking path followed.     

Thermal and mechanical properties of waste grass broom fiber-reinforced polyester composites

The main focus of this study is to utilize waste grass broom natural fibers as reinforcement and polyester resin as matrix for making partially biodegradable green composites. Thermal conductivity, specific heat capacity and thermal diffusivity of composites were investigated as a function of fiber content and temperature. The waste grass broom fiber has a tensile strength of 297.58 MPa, modulus of 18.28 GPa, and an effective density of 864 kg/m³. The volume fraction of fibers in the composites was varied from 0.163 to 0.358. Thermal conductivity of unidirectional composites was investigated experimentally by a guarded heat flow meter method. The results show that the thermal conductivity of composite decreased with increase in fiber content and the quite opposite trend was observed with respect to temperature. Moreover, the experimental results of thermal conductivity at different volume fractions were compared with two theoretical models. The specific heat capacity of the composite as measured by differential scanning calorimeter showed similar trend as that of the thermal conductivity. The variation in thermal diffusivity with respect to volume fraction of fiber and temperature was not so significant.The tensile strength and tensile modulus of the composites showed a maximum improvement of 222% and 173%, respectively over pure matrix. The work of fracture of the composites with maximum volume fraction of fibers was found to be 296 Jm⁻¹.