Fibre composites -matrices and fibres

Some of the main constituents nsed in these materials are discussed under Fibre composites - matrices and fibres and practical aspects are considered under Fibre composites - joining and Fibre composites - processing techniques. 

It is obvious that before the advantage of Composite materials (see Fibre composites - introduction) can be practically realized, they must be fabricated into components. Depending on the particular materials involved (see Fibre composites - matrices and fibres) and the forms required, specially developed processing methods may be necessary. Following is a brief survey of some of the more generally applicable procedures. 

Fibre composites - matrices and fibres B C COPE Scope of different fibre and matrix materials... 

The bar-chart of moduli (Fig. 3.5) shows that composites can have moduli much higher than those of their matrices. And it also shows that they can be very anisotropic meaning that the modulus is higher in some directions than others. Wood is an example its modulus, measured parallel to the fibres, is about lOGNrn" at right angles to this, it is less than 1GN m . ... 

Rgure 8.6 Representation of the variety of polymer morphologies in solution and in the gel (or microgel) or solid states. In solution the conformation of the polymer depends on the nature of polymer-solvent interactions and whether or not the polymer chains associate to form micellar aggregates. Crystals of polymer and microcrystals can be prepared, and gels can be formed from covalently crosslinked or polymer chains associated by hydrogen bonding or hydrophobic interactions. Listed are the forms in which most polymers can be fabricated membranes, fibres, composites, matrices microspheres and microcapsules can also feature, as discussed later in this chapter. 

The modern composite materials, which merge the advantages of natural fibres with synthetic matrices and environmental goals, aim to go beyond the fibre competition during the last 100 years and to answer the new challenges. 

FRCs can be classified based on matrix and fibres. Based on fibre source, FRCs may be natural fibre reinforced and synthetic fibre reinforced. Based on fibre length, they can be continuous fibre reinforced and discontinuous fibre reinforced. But FRCs are generally classified based on matrix component. Thus according to the types of matrices stated earlier, composites are of three types (i) ceramic matrix composites (CMCs), (ii) metal matrix composites (MMCs) and (iii) organic matrix composites (OMCs). Organic matrix is subdivided into two classes, namely polymer matrix and carbon matrix. A short description of all these types of composites are discussed below. 

A tentative model has been proposed to relate the interfacial shear strength at the fibre-matrix interface, measured by a fragmentation test on single fibre composites, to the level of adhesion between both materials. This last quantity has been estimated from the surface properties of both the fibre and the matrix and was defined as the sum of dispersive and acid-base interactions. This new model clearly indicates that the micromechanical properties of a composites are mainly determined by the level of physical interactions established at the fibre-matrix interface and, in particular, by electron acceptor-donor interactions. Moreover, to a first approximation, our model is able to explain the stress transfer phenomenon through interfacial layers, such as crystalline interphases in semi-crystalline matrices and interphases of reduced mobility in elastomeric matrices. An estimation of the elastic moduli of these interphases can also be proposed. Furthermore, recent work [21] has shown that the level of interfacial adhesion plays a major role on the final performances (tensile, transverse and compressive strengths and strains) of unidirectional carbon fibre-PEEK composites. 

We can see that there have been many efforts to study oil palm fibers with various matrices and various treatments. However, the properties are still limited and cannot compete with the synthetic fibres. Further development is still needed before the composites can face the competition in the market. Some issues that have not been well studied and need further work regarding fiber and its composites are [24] ... 

The general properties of polymer-based Composite materials and the critical influence of interfacial adhesion are considered under Fibre composites - introduction. The section below summarizes the range of materials that may be used as fibres and matrices, which together serve to exploit the range of properties that may be obtained from composites. 

The fire characteristics of many FRP with different matrices and various fibres have been studied [191-195]. Fleat resistant composites with very low smoke density, toxicity and corrosivity were obtained with a group of flame retardants (based on dihydrobenzoxazines) which don t contain halogen, sulfur or phosphorus [196]. Also, glass fibre reinforced resole phenolic composites have some outstanding fire properties, e.g., low RHR and low toxic smoke emissions [197]. 

Stress concentrations for linear elastic matrices and fibres have been calculated in [5] and [6]. The stresses are maximum at or near the interface. The composite interlaminar shear strength (ILSS) is SCF times lower than the interface strength x. when fracture initiates at the interface. The composite strength predicted by such calculations decreases with increasing fibre volume fraction. The decrease is very strong near the maximum packing density. These predictions may be too pessimistic because any yield behaviour will reduce the stress concentrations. 

Fibre-reinforced polymer (FRP) composites are composed of fibres and matrices, which are bonded through the interface to ensure that the composite system as a whole gives satisfactory performance. Part 1 deals with FRP composite matrix materials which provide the foundation for composite materials. Chapter 2 reviews the chemistry of phenolic resins together with their mechanical and thermal properties. Chapter 3 discusses polyester thermoset resins as matrix materials. An overview of the chemistry of vinylester resins, together with their mechanical and chemical properties, as well as their use as a matrix material in the construction industry, is provided in Chapter 4. The final chapter in Part 1 begins with a review of the epoxy resins commonly available on the market, and then focuses on the principal characteristics of epoxy resin composite systems and their practical applications. 

The properties of the fibres, the matrices and the fibre arrangement within the composite and the fibre volume fraction govern the final strength and stiffness value properties of the composites. These parameters have been illustrated in Hollaway and Teng (2008) and Smith and Yeomans (2002). The matrices for the composites that could be used in the manufacture of wind turbine blades would be polyester, vinylester or epoxies. Glass, Kevlar or carbon fibres can be used with any of the polymers mentioned, but as the rotor blades become larger a hybrid construction of glass and carbon is used. The hybrid concept is often a compromise between the improved... 

The polymer matrices and their fibre-reinforced versions can be ranked based on their fracture toughness value into three main groups, i.e. polymers and composites with K ... 

Materials such as metal, plastic, wood, paper, and leather are coated with pofymers primarily for protection and for the improvement of their properties. For this purpose, cellulose acetate (CA), cellulose acetate propionate (CAP), and cellulose acetate butyrate (CAB) are the most important classical and solvent-based cellulose esters of the coating industry [44]. Cellulose esters are widely used in composites and laminates as binder, filler, and laminate %ers. In combination with natural fibres, they can be used to some extent as composites from sustainable raw materials with good biodegradability. An additional domain of cellulose esters is their use in controlled-release systems, as well as membranes and other separation media [44, 47]. In the field of controlled-release systems, eellulose esters are used as enteric coatings, hydro-phobic matrices, and semipermeable membranes for appheations in pharmacy, agriculture, and cosmetics. 

Composite elements with Portland cement matrices and textile reinforcement have been used for some time as thin roof plates, partition walls, cladding, and the like. Some discussion of textile reinforcement is presented in Section 5.9. As well as systems of plane fabrics, three-dimensional (3D) reinforcement is also manufactured and there have been tests of elements with 3D carbon fibre reinforcement (Zia et al. 1992). 

The orientation of fibres is an important factor in the design of a composite material strncture. Strong anisotropic effects may be created by fibres and there have been several attempts both to determine the influence of fibre orientation on mechanical properties and to optimize it. Much of the research was concentrated on advanced composites with ductile matrices and the objective function for design or optimization was the composite strength. These composites were extensively applied not just in aircraft and rockets, but also in the construction of cars the review of these investigations is published by Ashby and Jones (2005). 

Both presented theories lead to similar conclusions concerning the cracking strain of reinforced matrices however, both exaggerate the influence of fibres. After the crack opening, the ACK theory may be used to calculate the probable crack spacing and the composite s Young s modulus. Furthermore, in that theory, a few of the parameters used are taken from the testing of relevant composite elements and therefore it is to some extent more appropriate for verification and calibration than other proposed theories for fibre-reinforced composites. 

As with conventional composites, when creating self-reinforced composites by combining discrete fibres and matrices such as by film and fibre stacking, various authors have also reported the surface pretreatment of the fibres to improve the interfacial properties of the composites [48, 51, 52]. However, details such as fibre preparation treatments and failure modes that dominate during specimen failure will not be presented in detail here. Instead, the focus of this review is the performance of the composite systems, and the reader is encouraged to consult the referenced literature for more details on the failure modes that dominate. 

Properties of typical thermosetting and thermoplastic polymer matrices and single fibres are listed. The former have relevance to the upper working temperature and off-axis properties of the composite, while the latter can be used to estimate composite strength and stiffness parallel to the fibre direction. 

The data presented here have been selected with the aid of the RAPRA database on reinforced plastics and composites, from commercial trade literature and sources, from the composites literature and the authors and their colleagues private sources. We have always tried to select information on well-prepared and described systems using modern fibre types and matrices. Inevitably it has not always been possible to do this and in some cases we have had to use older data, information where the fibre or resin is not fully specified or material for other than unidirectional systems. In doing this we have had to balance the need for information with the uncertainties mentioned, but where we have done this we believe that the information quoted, though not ideal, is the best way of filling a real gap. 

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