Natural fibre composites: Comprehensive Ashby-type materials selection charts

To aid design engineers in closing the existing gap between current scientific knowledge and actual market applications of plant fibre reinforced plastics (PFRPs), this article provides comprehensive Ashby-type materials selection charts for PFRPs to facilitate product design and development. General tensile mechanical property profiles are presented for a variety of PFRPs to enable the design for (i) optimal stiffness and strength, (ii) minimal weight (i.e. optimal specific properties), (iii) minimal cost, and (iv) minimal eco-impact. A large database is used to capture the range in properties of different (i) reinforcements forms (short fibres: pellets and nonwovens; long fibres: multiaxials and unidirectionals), (ii) polymer matrices (thermoplastic and thermosetting), and (iii) manufacturing techniques (injection moulding, compression moulding, hand lay-up, vacuum infusion, resin transfer moulding and prepregging). As PFRPs are often viewed as alternatives to glass fibre composites (GFRPs), for demonstrative purposes the tensile properties of the various PFRPs are compared with similar GFRPs. Moreover, highlighting that other mechanical parameters may be critical performance indices for specific products and applications, a materials property chart for a fatigue-limited design is also produced.     

Wood fibre-reinforced cement composites

The use of wood fibres as reinforcement for a structural composite material has been investigated. Although wood fibres have relatively poor mechanical properties compared with synthetic fibres, they have the advantages of low density, low cost and low energy demand during manufacture. A number of possible matrix materials were considered and Portland cement was chosen for further investigation. An examination was made of the effect of the pulping technique used to prepare the fibre on the strength of the composite and on the stability of the wood fibres in the cement matrix. A chemically pretreated high-temperature thermomechanical pulp and a pulp produced by the kraft process were selected for further study. The effect of the water-cement ratio of the matrix and the weight of fibre in the composite on the strength of the composite and the rate of increase in strength and fracture energy of composite are reported for composites containing these pulps. The results indicate that the kraft pulp is suitable for applications where slurry dewatering can be employed during the forming operation and that the thermomechanical pulp is more suited to applications where low water-cement ratio slurry is used.     

Fire structural resistance of basalt fibre composite

Basalt fibres are emerging as a replacement to E-glass fibres in polymer matrix composites for selected applications. In this study, the fire structural resistance of a basalt fibre composite is determined experimentally and analytically, and it is compared against an equivalent laminate reinforced with E-glass fibres. When exposed to the same radiant heat flux, the basalt fibre composite heated up more rapidly and reached higher temperatures than the glass fibre laminate due to its higher thermal emissivity. The tensile structural survivability of the basalt fibre composite was inferior to the glass fibre laminate when exposed to the same radiant heat flux. Tensile softening of both materials occurred by thermal softening and decomposition of the polymer matrix and weakening of the fibre reinforcement, which occur at similar rates. The inferior fire resistance of the basalt fibre composite is due mainly to higher emissivity, which causes it to become hotter in fire.     

Carbon/Carbon – an inverse composite structure

Carbon/carbon composites are a type of material, which combines the refractory properties of carbon with the high strength and stiffness of carbon fibres. Although one could not expect a reinforcement by the combination of a carbon matrix with carbon fibres the fibre properties can be used. Additionally the material shows a pseudoplastic fracture behaviour in spite of its ceramic nature. Explanations for this inverse behaviour in comparison to other composite structures will be presented including mechanical viewpoints, interactions at the interface between fibre and matrix, their influence to the fracture characteristics and micromechanical behaviour as well as the interactions between modulus and microstructure. Furtheron examples for some industrial applications are described.     

Novel basalt fibre reinforced glass matrix composites

A novel hot-pressing technique for the manufacturing of basalt fibre reinforced glass matrix composites was investigated. Two-dimensional (2D) fibre mats were sandwiched between borosilicate glass powder layers, thus configuring a much simpler processing route than that commonly employed for the production of fibre-reinforced glasses. Besides economic benefits, the use of fibre mats may lead to technologic advantages due to the possibility of readily coating the fibres with a suitable material (e.g. titanium oxide) by means of the sol-gel method. The coating of basalt fibre mats with TiO₂ is proposed for preventing the fibres from an excessive adhesion to the glass matrix. The developed composites containing 15 vol% of 2D-fibre reinforcement exhibited promising bending strength (∼90 MPa) and desirable “graceful” fracture behaviour without catastrophic failure. Thus the present study represents a convenient approach for production of advanced low-cost fibre reinforced glass matrix composites for structural applications.     

A review on basalt fibre and its composites

In recent years, both industrial and academic world are focussing their attention toward the development of sustainable composites, reinforced with natural fibres. In particular, among the natural fibres (i.e. animal, vegetable or mineral) that can be used as reinforcement, the basalt ones represent the most interesting for their properties. The aim of this review is to illustrate the results of research on this topical subject. In the introduction, mechanical, thermal and chemical properties of basalt fibre have been reviewed. Moreover, its main manufacturing technologies have been described. Then, the effect of using this mineral fibre as reinforcement of different matrices as polymer (both thermoplastic and thermoset), metal and concrete has been presented. Furthermore, an overview on the application of this fibre in biodegradable matrix composites and in hybrid composites has been provided. Finally, the studies on the industrial applications of basalt fibre reinforced composites have been reviewed.     

Mechanical and tribological properties of zinc-aluminium metal-matrix composites

Recently, commercial Zn-Al foundry alloys such as ZA-27 have found increasing use for many applications and have competed effectively against copper, aluminium and iron-based foundry alloys. However, the elevated temperature (> 100°C) properties of zinc-aluminium alloys are unsatisfactory and restrict their use in some applications. One viable approach to improving the elevated temperature properties is to reinforce the zinc-aluminium alloys with alumina fibres. In this investigation, the mechanical properties of a Zn-Al alloy reinforced with alumina fibres were evaluated. Tensile, compression and impact properties were determined at 25, 100 and 150°C. Lubricated wear tests were also performed on the unreinforced alloy and composites. It was found that although fibre reinforcement did result in some improvement of tensile and compression properties at elevated temperatures, the composites had poor toughness and ductility. The presence of a brittle SiO₂ layer at the fibre/matrix interfaces resulted in fibre/matrix decohesion under tensile loading, impairing the performance of the reinforced materials. Some improvement in wear resistance was noted for the composite materials but fibre reinforcement did not yield significant improvement in fatigue resistance.     

Interfacial characterization of Nicalon SiC fibre reinforced oxynitride glass matrix composites

Nicalon SiC and Hi-Nicalon SiC fibre oxynitride glass and glass–ceramic composites were prepared and the interface between the fibres and matrix characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) spectroscopy. It was found that the formation and thicknesses of interfacial layers were primarily determined by the type of fibre reinforcement, but the role of these interfaces in influencing composite properties was dependent on the thermal properties of the matrix. For Nicalon SiC composites, the carbon-rich layer did not promote fibre debonding and toughening unless the matrix had a smaller thermal expansion coefficient than the fibres. For Hi-Nicalon SiC composites, the absence of oxygen in the fibre significantly encouraged chemical reaction between fibre and matrix, resulting in no strengthening or toughening. This revised version was published online in November 2006 with corrections to the Cover Date.     

Development of durable cementitious composites using sisal and flax fabrics for reinforcement of masonry structures

Natural fibres are one of the most studied materials. However, the use of these fibres as reinforcements in composite materials for structural applications, especially for existing or historical masonry structures, remains a challenge. In this study, efforts were made to develop sustainable composites using cementitious matrices reinforced with untreated bi-directional fabrics of natural fibres, namely, flax and sisal fibres. The fibres were mechanically characterised by tensile tests performed on both single yarns and fabric strips. Ageing effects due to fibre mineralisation in alkaline cement paste environments may cause a reduction in the tensile strength of natural fibres. The matrices used to study fibre durability were a natural hydraulic lime-based mortar (NLM) mix with a low content of water-soluble salts and a lime-based grouting (NLG) mix containing natural pozzolans and carbonated filler. Tensile tests on impregnated single yarns subjected to wetting and drying cycles by exposure to external weathering were conducted at different ages to quantify these problems. Composite specimens were manufactured by the hand lay-up moulding technique using untreated fibre strips and an NLG matrix. The mechanical response of natural fibre reinforced cementitious (NFRC) composites was measured under tension, and the effect of the matrix thickness was also addressed. Both sisal and flax fibres showed good adhesion with the NLG matrix, making them capable of producing composites with ductile behaviour and suitable mechanical performance for strengthening applications in masonry structures.     

Plâtres renforcés de fibres cellulosiques

Tensile strength and toughness of plaster is highly improved by fibre reinforcement, specially because of the delaying action of the fibres on crack propagation. The conditions required for an optimal reinforcement are a low porosity of the matrix, a uniform distribution of the fibres and a good connection between fibres and matrix. The water/plaster ratio affects the physical (density) and mechanical properties of plaster: water content in excess results in a low-density porous material. A wet process is used for making fibre-plaster composites; since cellulosic fibres have also a strong interaction with water, the effect of casting duration and water content on the mechanical performance of fibre reinforced plasters are presented and discussed in this paper.     

Flax fibre and its composites – A review

In recent years, the use of flax fibres as reinforcement in composites has gained popularity due to an increasing requirement for developing sustainable materials. Flax fibres are cost-effective and offer specific mechanical properties comparable to those of glass fibres. Composites made of flax fibres with thermoplastic, thermoset, and biodegradable matrices have exhibited good mechanical properties. This review presents a summary of recent developments of flax fibre and its composites. Firstly, the fibre structure, mechanical properties, cost, the effect of various parameters (i.e. relative humidity, various physical/chemical treatments, gauge length, fibre diameter, fibre location in a stem, oleaginous, mechanical defects such as kink bands) on tensile properties of flax fibre have been reviewed. Secondly, the effect of fibre configuration (i.e. in forms of fabric, mat, yarn, roving and monofilament), manufacturing processes, fibre volume, and fibre/matrix interface parameters on the mechanical properties of flax fibre reinforced composites have been reviewed. Next, the studies of life cycle assessment and durability investigation of flax fibre reinforced composites have been reviewed.     

Use of electrophoretic deposition in the processing of fibre reinforced ceramic and glass matrix composites: a review

Electrophoretic deposition (EPD) is a simple and cost-effective method for fabricating high-quality ‘green’ composite bodies which, after a suitable high-temperature treatment, can be densified to a composite with improved properties. In this contribution, we describe the use of EPD technique in the fabrication of fibre reinforced composites, with an emphasis on composites with glass and ceramic matrices containing metallic or ceramic fibre fabric reinforcement. EPD has been used to infiltrate preforms with tight fibre weave architectures using different nanosized ceramic particles, including silica and boehmite sols, as well as dual-component sols of mullite composition. The principles of the EPD technique are briefly explained and the different factors affecting the EPD behaviour of ceramic sols and their optimisation to obtain high infiltration of the fibre preforms are considered. In particular, the EPD fabrication of a model alumina matrix composite reinforced by Ni-coated carbon fibres is presented. The pH of the solution and the applied voltage and deposition time are shown to have a strong influence on the quality of the infiltration. Good particle packing and a high solids-loading were achieved in most cases, producing a firm ceramic deposit which adhered to the fibres. Overall, the analysis of the published data and our own results demonstrate that EPD, being simple and inexpensive, provides an attractive alternative for ceramic infiltration and coating of fibre fabrics, even if they exhibit tight fibre weave architectures. The high-quality infiltrated fibre mats are suitable prepregs for the fabrication of advanced glass and ceramic matrix composites for use in heat-resistant, structural components.     

High performance carbon-carbon composites

Carbon-carbon composites rank first among ceramic composite materials with a spectrum of properties and applications in various sectors. These composites are made of fibres in various directions and carbonaceous polymers and hydrocarbons as matrix precursors. Their density and properties depend on the type and volume fraction of reinforcement, matrix precursor used and end heat treatment temperature. Composites made with thermosetting resins as matrix precursors possess low densities (1.55–1.75g/cm³) and well-distributed microporosity whereas those made with pitch as the matrix precursor, after densification exhibit densities of 1.8–2.0g/cm³ with some mesopores, and those made by the CVD technique with hydrocarbon gases, possess intermediate densities and matrices with close porosities. The former (resin-based) composites exhibit high flexural strength, low toughness and low thermal conductivity, whereas the latter (pitch- and CVD-based) can be made with very high thermal conductivity (400–700 W/MK) in the fibre direction. Carbon-carbon composites are used in a variety of sectors requiring high mechanical properties at elevated temperatures, good frictional properties for brake pads in high speed vehicles or high thermal conductivity for thermal management applications. However, for extended life applications, these composites need to be protected against oxidation either through matrix modification with Si, Zr, Hf etc. or by multilayer oxidation protection coatings consisting of SiC, silica, zircon etc.     

Polyester-based biocomposites containing wool fibres

Biocomposites based on a biodegradable polyester containing different amounts of wool fibres (up to 40 wt.%) were prepared by melt blending in an internal batch mixer. Wool fibres were used as received or pre-treated in order to preserve a high aspect ratio and increase adhesion with polymer matrix. Morphological, thermal, mechanical and dynamic-mechanical properties of the ensuing composites were investigated focusing the attention on fibre length and their distribution as well as on fibre/matrix interaction in order to correlate these aspects with polymer reinforcement. Data from mechanical and dynamic-mechanical analysis were also compared with theoretical models.     

Tensile failure mechanisms in synthetic fibre-reinforced mortar

The ultimate tensile behaviour of fibre-reinforced cementitious composites is closely related to its failure mechanisms which in turn are dependent on reinforcement parameters such as fibre characteristics and the fibre/matrix interface properties. Based on the direct tensile tests of mortar specimens reinforced with various synthetic fibres, this paper attempts to explain such relationships and to indicate directions towards more effective fibre reinforcement.     

Analysis of Mechanical Properties of Injection Molded Short Glass Fibre (SGF)/Calcite/ABS Composites

Acrylonitrile-butadiene-Styrene (ABS), with and without calcium carbonate (calcite) particles,was used as the matrix for reinforcement with as-received short-glass fibres (were originallytreated by the manufacturer) and sized short-glass fibres with two amino-silane coupling agents.The calcite particle content is 0, 11.7 and 23.5 vol. pct for the matrices. The glass fiber contentis 0, 10 and 15 vol. pct. The matrix materials and corresponding composites were compoundedusing a twin screw extruder and dumbbell-shaped tensile bars were prepared with an injectionmolding process. The tensile and flexural properties as well as the unnotched and notchedCharpy impact energies of short glass fibre/calcite/ABS composites were studied in this paper.The effects of fibres, fibre surface treatments and particles on these mechanical properties ofthe composites were discussed in detail. An importarit information was obtained, which is thatthe tensile and flexural strengths of hybrid SGF/calcite/ABS composites are the same as thoseof corresponding fibre composites when the ratio of the interfacial adhesion strength betweenparticles and matrix to that between fibres and matrix is higher than certain value. otherwise theformer are lower than the latter.     

Potentiality of utilising natural textile materials for engineering composites applications

This paper gives an overview of utilising natural textile materials as reinforcements for engineering composites applications. The definition and types of textile materials are addressed to provide readers a thoughtful view on the role of these materials in a structural composite system. Available material properties of natural textile and their composites are critically reviewed here. In general, these materials are categorised into fibre, yarn and fabric forms. The load bearing capacity of natural textile fibre reinforced polymer composites is governed by the quantity, alignment and dispersion properties of fibres. It has been found that the natural fibre reinforced composites are limited to use in low to medium load bearing applications. However, a limited research work has been performed to date and there is a significant gap between the high performance textile fabric and their use as reinforcement in fibre reinforced composite materials.     

Dental application of various kinds of fibres in heat curing acrylic resin

The effect of the type of fibres on bending behaviour and impact energy in reinforced acrylic resin was examined. Reinforcing materials such as inorganic glass fibre and cloth and organic polyester and Kevlar fibres were coated with a silane coupling treatment, whereas Co-Cr wire was directly used for the reinforcement. After silane coupling treatment each fibre was added to the heat curing base resin, except polyester fibre. It is concluded that the inclusion of glass linear fibre provides an effective improvement on plain acrylic base resin. An additional way to reinforce the resin matrix was given by the combined use of glass and Kevlar fibres.     

Finite Element Assisted Modelling of the Microscopic Impregnation Process in Thermoplastic Preforms

Fibre reinforced composite materials incorporating thermoplastic matrices are gaining increasing popularity in many industrial applications. One of the potential preforms for the manufacture of technical components is commingled yarn composed of reinforcement and matrix in fibre form. These are often employed in the pultrusion process. Another innovative preform consists of polymer powder preimpregnated sheath surrounding fibre bundles. To achieve adequate mechanical properties of the final product it is essential, when producing laminates by a process such as pultrusion with both types of preform, that sufficient matrix impregnation is achieved. The prevention of voids and dry-spots in the laminate requires a theoretical understanding of the mechanisms involved. On a microscopic scale, several finite element (FE) models can be used to simulate the progress of the matrix flow into the interstitial spaces between the single reinforcement fibres. In the present simulations, a hexagonal and a square arrangement account for two of the various fibre packings occurring in a laminate. It permits an estimation of the impregnation performance of commingled and powder impregnated yarns. For each preform the shear rate, to which the polymer matrix is subjected during the impregnation and consolidation process, can be predicted.     

The effect of mechanical defects on the strength distribution of elementary flax fibres

Flax fibres are finding non-traditional applications as reinforcement of composite materials. The mechanical properties of fibres are affected by the natural variability in plant as well as the damage accumulated during processing, and thus have considerable variability that necessitates statistical treatment of fibre characteristics. The strength distribution of elementary flax fibres has been determined at several fibre lengths by standard tensile tests, and the amount of kink bands in the fibres evaluated by optical microscopy. Strength distribution function, based on the assumption that the presence of kink bands limits fibre strength, is derived and found to provide reasonable agreement with test results.