Carbon fibres, tensile properties

The mechanical properties of plastics materials may often be considerably enhanced by embedding fibrous materials in the polymer matrix. Whilst such techniques have been applied to thermoplastics the greatest developents have taken place with the thermosetting plastics. The most common reinforcing materials are glass and cotton fibres but many other materials ranging from paper to carbon fibre are used. The fibres normally have moduli of elasticity substantially greater than shown by the resin so that under tensile stress much of the load is borne by the fibre. The modulus of the composite is intermediate to that of the fibre and that of the resin. 

ISO 10618 2004 Carbon fibre - Determination of tensile properties of resin-impregnated yarn... 

ISO 11566 1996 Carbon fibre - Determination of the tensile properties of single-filament specimens... 

By use of this functionally gradient coating the carbon-fibre-reinforced aluminium composites (C/Al) exhibit excellent mechanical properties. The ultimate tensile strength reaches 1250 MPa when the fibre volume fraction is 35%. 

One common characteristic of all C/SiC composites is their distinct anisotropy in the mechanical as well as thermophysical properties. Considerable lower values of the tensile strength and the strain to failure have to be considered for an appropriate design if the load direction and the fibre alignment are not congment. As the carbon fibres show a different physical behaviour in longitudinal and radial direction, the composite s properties like thermal conductivity and coefficient of thermal expansion differ widely with respect to the in-plane or transverse direction. 

Fujita A, Hamada H, Maekawa Z. Tensile properties of carbon fibre triaxial woven fabric composites. J Compos Mater 1993 27 1428 2. 

M. Guigon and A. Oberlin, Heat treatment of high tensile strength PAN-based carbon fibres microtexture and mechanical properties. Composites Sci. Tech., 27,1-23 (1986). 

Figure 3.16 Tensile strengths of reinforced Type II electroplated and hot-pressed copper. Broken line as predicted by Law of Mixtures. Source Reprinted with permission from Howlett BW, Minty DC, Old CF, The fabrication and properties of carbon fibre/metal composites, Paper No. 14, International Conference on Carbon Fibres and Applications, The Plastics Institute, London, 1971. Copyright 1971, Maney Publishing (who administers the copyright on behalf of lOM Communication Ltd, a wholly owned subsidiary of the Institute of Materials, Minerals Mininng).

Figure 5.58 Fiber tensile strength as a function of heat treatment, measured by single filament test with 30 mm gage length at a crosshead speed of 1 mm min Source Reprinted with permission from Fitzer E, Frohs W, The influence of carbonization and post heat treatment conditions on the properties of PAN-based carbon fibres, Presented at Carbon 88, Newcastle upon Tyne, 298-300, 1988. Copyright 1988, The Insitute of Physics Publishing.

Fu X, Lu W, Chung DDL, Improving the tensile properties of carbon fibre reinforced cement by ozone treatment of the fibre, Cem Concr Res, 26(10), 1485-1488, 1996. 

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. 

In almost all flexural tests the specimens failed in the upper stratus, due to compression stresses. This can be explained by means of the mechanical properties of carbon fibres. The compression strength of carbon fibres are about 90 % of the value of the tensile strength. Therefore, cracks are developed by compression stresses. 

Although natural fibres are highly comparable to conventional glass fibres on a per weight basis, the major drawback arises from the inherent variabUity of natural fibres [22]. Natural fibres can vary in terms of their dimensions and mechanical properties, even within the same cultivation. This situation is different from synthetic fibres, which can be manufactured uniformly (e.g., Toray s T700S carbon fibre has only a variability of 10% in its tensile strength and modulus [Commercial documentation - No AQ.866-9 (September 2003), Personal communication], 3% in its diameter). All natural fibres are hydrophilic in nature due to the presence... 

The effect of surface treatment on the mechanical properties of carbon-fibre composites Brittle fibres in a brittle matrix can have appreciable toughness because the cracks can get diverted along the fibre-matrix interface. If the bond is weak the composite will not support loads in shear or compression, but when the bond is too strong, the material will be brittle. These aspects are illustrated in Fig. 6, where it is seen that the interlaminar shear strength reaches a plateau but the notched tensile strength decreases... 

Loos (2011) reported that investigators from Bayer Material Science LLC, USA and Moulded Fibre Glass, Cleveland, USA have developed a prototype wind turbine blade 0.74 m long manufactured from polyurethane reinforced with carbon nanotubes (CNT PU). The researchers claim that the advanced material has a specific tensile strength five times and 60 times that of carbon fibre composite and aluminium, respectively, and is tougher than carbon fibre-reinforced polymer (CFRP) but the excellent properties of these materials come with a price penalty. 

PVF (20% carbon fibre reinforced) 100 5.5 6 N/R 0.12 High tensile strength, flexural modulus, heat desorption temperature, detergent resistance and hydrolytic stability Elongation at break, gamma ray resistance, dielectric properties, surface finish and toughness... 

Some engineering applications of polymers reinforced with glass fibre and carbon fibres are shown in Tables 2.4 and 2.5. It is seen that there are wide ranges of applications particularly in glass fibre, carbon fibre and nanotubes. Many of these applications require polymers, which have a particularly high standard of properties, for example, stability in impact and tensile properties, thermal properties, dimensional stability and, chemical and oil resistance. 

Tensile properties of the HDPE/RET blend are shown in Table 8.2. The HDPE 100/0 carbon-fibre composite showed complete linear stress-strain behaviour up to its ultimate tensile strength and fracture at 10.3% strain. No definitive fracture was seen in the HDPE blends. This is due to the interfacial de-bonding between the constituents within the polymer. The apparent loss of cohesive strength of the matrix material resulted in fibre pull-out and interlaminar slip between the carbon-fibre plies. 

Table 8.2 Tensile properties of HDPE/RET carbon fibre composites ...

The third of these belong to the HT type with high tensile strength and improved stiffness. Table 6.11 shows some mechanical properties of different types of carbon fibres. 

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