Composite materials continuous fibres

Compounds are short (/w 0.3 mm) or long (> 0.6 mm) fibre reinforced thermoplastic or thermoset polymeric materials, which are processed automatically (injection or compression moulding), have good (mechanical) properties (for automotive, electric and electronic applications) and are relatively cheap. Composites contain continuous fibres (rovings, fabrics or mats), usually combined with thermosets, have excellent mechanical (structural) properties, but are very expensive because lack of an industrial process (mainly used in aerospace and aircraft industry). 

For the composites with continuous fibres, a great number of criteria are available, such as those of deformation or of the maximal effort, and the Tsai/Hill criterion or TsaiAVu criterion. In accordance with these criteria, the composite materials will be broken when one of the mechanical components reaches a limit value (experimentally determined, in the majority of cases). The Tsai/Hill criterion defines the upper limit of the effort, above which the fracture occur ... 

Galculate the upper and lower values for the modulus of the composite material, and plot them, together with the data, as a function of Vf. Which set of values most nearly describes the results Why How does the modulus of a random chopped-fibre composite differ from those of an aligned continuous-fibre composite ... 

For many applications (e.g. body pressings), it is inconvenient to use continuous fibres. It is a remarkable feature of these materials that chopped fibre composites (convenient for moulding operations) are nearly as strong as those with continuous fibres, provided the fibre length exceeds a critical value. 

This is more than one-half of the strength of the continuous-fibre material (eqn. 25.3). Or it is if all the fibres are aligned along the loading direction. That, of course, will not be true in a chopped-fibre composite. In a car body, for instance, the fibres are randomly oriented in the plane of the panel. Then only a fraction of them - about - are aligned so that much tensile force is transferred to them, and the contributions of the fibres to the stiffness and strength are correspondingly reduced. 

R. L. Hewitt and M. C. de Malherbe, An Approximation for the Longitudinal Shear Modulus of Continuous Fibre Composites, Journal of Composite Materials, April 1970, pp. 280-282. 

Reinforcements in the form of continuous fibres, short fibres, whiskers or particles are available commercially. Continuous ceramic fibres are very attractive as reinforcements in high-temperature structural materials. They provide high strength and elastic modulus with high temperature-resistant capability and are free from environmental attack. Ceramic reinforcement materials are divided into oxide and non-oxide categories, listed in Table 3.1. The chemical compositions of some commercially available oxide and non-oxide reinforcements are given in Table 3.2 and Table 3.3. 

Whisker-reinforced glass-ceramic matrices are expected to find several applications in automotive components, metal forming, cutting tools, etc., due to their low thermal expansion, high thermal shock resistance, high reliability and low material and processing costs. Some industrial applications for continuous fibre-reinforced ceramic matrix composites (CMCs) are listed below. 

Research on the pyrolysis of thermoset plastics is less common than thermoplastic pyrolysis research. Thermosets are most often used in composite materials which contain many different components, mainly fibre reinforcement, fillers and the thermoset or polymer, which is the matrix or continuous phase. There has been interest in the application of the technology of pyrolysis to recycle composite plastics [25, 26]. Product yields of gas, oil/wax and char are complicated and misleading because of the wide variety of formulations used in the production of the composite. For example, a high amount of filler and fibre reinforcement results in a high solid residue and inevitably a reduced gas and oiFwax yield. Similarly, in many cases, the polymeric resin is a mixture of different thermosets and thermoplastics and for real-world samples, the formulation is proprietary information. Table 11.4 shows the product yield for the pyrolysis of polyurethane, polyester, polyamide and polycarbonate in a fluidized-bed pyrolysis reactor [9]. 

Additional increase of properties of titanium-based materials is associated with composites. For example, reinforcement due to continuous fibres of silicon carbide (up to 40-wt.%) permits strength and rigidity of such materials to be essentially increased. However, the cost of such composites appears to be prohibitive (about several tens of thousands of USD per 1-kg [19], Moreover, above temperatures of 600 °C an interaction of fibers and matrix is revealed. 

A solid structural substance produced by a combination of two or more materials that retain their identities. Typically, one of the materials combined is the strengthening agent, the other being the matrix (a thermoset or a thermoplastic resin). The word composite is also used for systems that are reinforced (reinforced where cumulative properties are superior to the individual components) by addition of certain solid particles (i.e., short fibre composites - long fibre composites - continuous fibre composites). 

The best initial mechanical properties are achieved with continuous fibre composites. Table 2.3 gives some representative values. The numbers refer to the properties of the materials in their original (as-manufactured) condition. After several years in service, the properties will not be the same, even in the absence of obvious mechanical damage. It is customary to cite the change in properties with time as a measure of the extent of deterioration, and % retention has become by implication a measure of durability. Not all properties change equally rapidly and the selection of significant properties requires careful consideration. 

Because of the virtually unlimited variations in fibre arrangements (short and continuous fibres, aligned and randomly distributed, laminated, woven, knitted or braided) there are too many materials available to discuss fully all the details of their fatigue behaviour. This chapter will therefore concentrate on some selected composites for demonstration purposes. We shall discuss both tension fatigue, which is the most important load situation in metals, and compression fatigue. The influence of harsh environments will be mentioned as well. 

Glass and glass-ceramic composite materials with alternative designed microstmctures have received much less attention in the past than their classic counterparts, namely dispersion-reinforced and continuous fibre-reinforced glass and glass-ceramic matrix composites (discussed in the previous Chapters 20 and 19, respectively). Due to their particular microstmcture, these composites may display a range of properties not achievable with... 

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