Composite materials fibre composites

Usually, the fibres are not unidirectional oriented in composite materials. Fibres orientation varies in function of the pieces thickness, processing method, and mould geometry. Accepting a random orientation of fibres, or a known and measured orientation, the laminates theory was appealed in order to describe the behaviour of this type of composites. The method allows the determination of the weakest layers, which will be firstly fractured [1285]. The Figure 3.456 illustrates a good agreement between the theory and practice, considering, for comparison, the data furnished by P.E. Chen [1285] and J.K. Lees [1286]. 

The distinction between composite materials and composite structures is not sharp and laminated composites form a group that may be logically considered for different purposes either as materials or as structures. Composite materials are used to build up composite structures, but homogeneous ones may also be used. It is usual to consider concrete and fibre-reinforced concrete as composite materials. A concrete beam reinforced with steel bars or a set of steel beams connected together with a concrete steel-reinforced slab to create... 

A. R. BunseU, ed.. Fibre Reinforcements for Composite Materials, Elsevier Science Publishing Co. Inc., New York, 1988. 

This comprises composite materials on mica, glass fibre and asbestos bases, impregnated or glued together with silicone resins or silicone elastomer. These materials must not contain any organic fibrous materials such as paper or cloth backing, which is covered under class B and even F insulation systems. 

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. 

A composite material for a car-repair kit consists of a random mixture of short glass fibres in a polyester matrix. Estimate the maximum toughness of the composite. You may assume that the volume fraction of glass is 30% the fibre diameter is 15 pm the fracture strength of the fibres is 1400 MPa and the shear strength of the matrix is 30 MPa. 

Jones, F.R., Interfacial aspects of glass fibre reinforced plastics. In Jones, F.R. (Ed.), Interfacial Phenomena in Composite Materials. Butterworths, London, 1989, pp. 25-32. Chaudhury, M.K., Gentle, T.M. and Plueddemann, E., Adhesion mechanism of poly(vinyl chloride) to silane primed metal surfaces. J. Adhes. Sci. Technol, 1(1), 29-38 (1987). Gellman, A.J., Naasz, B.M., Schmidt, R.G., Chaudhury, M.K, and Gentle, T.M., Secondary neutral mass spectrometry studies of germanium-silane coupling agent-polymer interphases. J. Adhes. Sci. Technol., 4(7), 597-601 (1990). 

In the early days nearly all thermosetting moulding materials were composites in that they contained fillers such as woodflour, mica, cellulose, etc to increase their strength. However, these were not generally regarded as reinforced materials in the sense that they did not contain fibres. 

This is an important relationship. It states that the modulus of a unidirectional fibre composite is proportional to the volume fractions of the materials in the composite. This is known as the Rule of Mixtures. It may also be used to determine the density of a composite as well as other properties such as the Poisson s Ratio, strength, thermal conductivity and electrical conductivity in the fibre direction. 

It is also worthy of note that large values of Poisson s Ratio can occur in a laminate. In this case a peak value of over 1.5 is observed - something which would be impossible in an isotropic material. Large values of Poisson s Ratio are a characteristic of unidirectional fibre composites and arise due to the coupling effects between extension and shear which were referred to earlier. 

Powell, P.C. Engineering with Fibre-Polymer Laminates, Chapman and Hall, London (1994). Daniel, I.M. and Ishai, O. Engineering Mechanics of Composite Materials, Oxford University Press (1994). 

Tsai, S.W. and Hahn, H.T. Introduction to Composite Materials, Technomic Westport, CT (1980). Folkes, M.J. Short Fibre Reinforced Thermoplastics, Research Studies E ress, Somerset (1982). Mathews, F.L. and Rawlings, R.D. Composite Materials Engineering and Science, Chapman and Hall, London (1993). 

A hybrid composite material is made up of 20% HS carbon fibres by weight and 30% E-glass fibres by weight in an epoxy matrix. If the density of the epoxy is 1300 kg/m and the data in Fig. 3.2 may be used for the fibres, calculate the density of the composite. 

The Z-direction is perpendicular to the page. For simplicity the material is assumed to be isotropic, ie same properties in all directions. However, in some cases for plastics and almost always for fibre composites, the properties will be anisotropic. Thus E and v will have different values in the x, y and z direction. Also, it should also be remembered that only at short times can E and v be assumed to be constants. They will both change with time and so for long-term loading, appropriate values should be used. 

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. 

Boron itself has been used for over two decades in filament form in various composites BO3/H2 is reacted at 1300° on the surface of a continuously moving tungsten fibre 12/tm in diameter. US production capacity is about 20 tonnes pa and the price in about 80(. The primary use so far has been in military aircraft and space shuttles, but boron fibre composites are also being studied as reinforcement materials for commercial aircraft. At the domestic level they are finding increasing application in golf shafts, tennis rackets and bicycle frames. 

N. L. Hancox, (ed.). Fibre Composite Hybrid Materials, McMillan, New York (1981). 

Particular examples of using polymer composites as screens are given in [14-16, 67-75], The present review does not touch the properties of the composite materials based on fabrics of conducting fibres due to the fact that manufacturing techniques for such materials are specific and differ greatly from the mixing processes considered above. However, these materials also have an application field, say, in contacts for calculator and computer keyboards [9] and even in small-power electric motor commutators as a partial substitute for copper [76, 77]. 

A significant amount of waste composites is generated each year and the need for a recycling method is becoming a necessity. Environmental Technical Services has developed, with the support of the University of Missouri-St.Louis, a method for recovering valuable constituents from composite materials. The process converts the polymer matrix to lower chain hydrocarbons and fuel gas leaving behind fibres. Mechanical tests of BMC panels, reinforced concrete and compression moulded panels made with recovered fibres were carried out. 10 refs. USA... 

Currently, scrap fibre-reinforced composite materials and prepregs are landfilled, although these materials represent... 

Journal of Thermoplastic Composite Materials 7, No.l, Jan.l994,p.64-74 NEW DEVELOPMENTS IN CHEMICAL RECYCLING AS A SINK FOR PROBLEMATIC WASTE FROM FIBRE-REINFORCED PLASTICS Menges G... 

We will confine ourselves to those applications concerned with chemical analysis, although the Raman microprobe also enables the stress and strain imposed in a sample to be examined. Externally applied stress-induced changes in intramolecular distances of the lattice structures are reflected in changes in the Raman spectrum, so that the technique may be used, for example, to study the local stresses and strains in polymer fibre and ceramic fibre composite materials. 

More data on polymers and other fibre-reinforced polymers can be found in the proceedings of various ICMC (International Cryogenic Materials Conference) meetings devoted to non-metallic materials and composites at low temperatures [113-117] and some special issues of the journal Cryogenics [118-120]. 

Finally, glass-reinforced unsaturated polyesters are well known as building materials for boats, yachts and cars and generally termed fibre-glass resin . The preparation, properties and applications of these unsaturated polyesters are summarized in Chapter 21, while the chemistry and properties of a new unsaturated polyester resin for fibre-reinforced composite materials are discussed in Chapter 22. 

The generally poorer mechanical properties exhibited by acetylated lignocellulosic material in composites bonded using aqueous resin systems was considered by Korai etal. (2001). Fibres of yellow cedar (Chamaecyparis nootkatensis) were acetylated to a WPG of 24.8 % and then ozonated to different extents to increase the hydrophilicity of the fibre surface. Boards were fabricated from the fibres using an aqueous MF resin. Ozonation improved IBS of boards fabricated from acetylated fibres, proportional to level of ozone charge, and resulted in IBS values comparable to those of nonacetylated controls at higher levels of ozonation. However, although ozonation also improved MOR, the values obtained for acetylated fibres were always less than those obtained with unmodified fibres. 

A.R. Bunsell, Fibre Reinforcements for Composite Materials, Elsevier... 

Riedel, U. (1999). Natural fibre-reinforced biopolymers as construction materials-new discoveries. 2nd International Wood and Natural Fibre Composites Symposium, June 28-29, Kassel/Germany, 1-10. 

A rubber-like copolymer/carbon fibre composite material has also been prepared [170]. Carbon fibres were added directly to o/w highly concentrated emulsions of block copolymers, such as styrene/butadiene triblocks (SBS), in toluene, followed by precipitation in methanol, drying and hot-pressing. The surfactant was found to aid adhesion between the polymer and carbon fibres. The materials obtained had fairly even distributions of carbon fibres, good mechanical properties and conductivities which increased with increasing carbon fibre length. 

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