Fibre-matrix composite

Predicting Of and T involves stress anafysis of the fibre-matrix composite under load. A simplified but highfy successful solution, is known as the shear lag themy (6.N.7). It assumes perfect bonding between fibres and matrix, and results in the following prediction of [Pg.275]

Ref. Lead author, year Polymer fibre/ matrix Composite architecture Consolidation technique Fibre fi action (%) Longitudinal modulus (GPa) Longitudinal strength (MPa) Transverse modulus (MPa) Transverse strength (MPa)... 

There is a simple way to estimate the modulus of a fibre-reinforced composite. Suppose we stress a composite, containing a volume fraction Vfo( fibres, parallel to the fibres (see Fig. 6.3(a)). Loaded in this direction, the strain, e , in the fibres and the matrix is the same. The stress carried by the composite is... 

This gives us an upper estimate for the modulus of our fibre-reinforced composite. The modulus cannot be greater than this, since the strain in the stiff fibres can never be greater than that in the matrix. 

Polymer-matrix composites for aerospace and transport are made by laying up glass, carbon or Kevlar fibres (Table 25.1) in an uncured mixture of resin and hardener. The resin cures, taking up the shape of the mould and bonding to the fibres. Many composites are based on epoxies, though there is now a trend to using the cheaper polyesters. 

Fig. 26.3. The molecular structure of a cell wall. It is a fibre-reinforced composite (cellulose fibres in o matrix of hemicellulose and lignin).

Bouix, J., Vincent, H., Boubehira, M., and Viala, J. C., Titanium Diboride-Coated Boron Fibre for Aluminum Matrix Composites, J. Less Common Metals, 117(l-2) 83-89 (Mar. 1986)... 

ASTM D 3171-90 describes a standard test method for fibre content determination of resin-matrix composites by matrix digestion in a hot medium, such as HNO3 or H2SO4/H2O2 [53],... 

Lanxide A process for making composites of metals with oxides. A molten metal reacts with an adjacent oxidant and is progressively drawn through its own oxidation product so as to yield a ceramic/metal composite. Fibres or other reinforcing materials can be placed in the path of the oxidation reaction and so incorporated in the final product. The Lanxide Corporation was founded in 1983 in Newark, DE, to exploit this invention. In 1990 it formed a joint venture with Du Pont to make electronic components by this process. Variations are Dimox (directed metal oxidation), for making ceramic metal composites, and Primex (pressureless infiltration by metal), for making metal matrix composites. 

The lifetime of advanced composite components for use in aircraft is governed primarily by allowable deformation or by fatigue. The fatigue behaviour has been the subject of many years testing by the aircraft companies, generating empirical load-cycle curves for many combinations of fibre, matrix and orientation. Humidity ingress (diffusion... 

Depending on the rigidity and the ductility of the matrix, when a stress is applied to a short glass fibre reinforced composite the following steps can be observed ... 

Chemical vapour deposition (CVD) is employed to prepare adherent films of controlled composition and thickness. Protective coatings, micro- and opto-electronics, ceramic fibres and ceramic-matrix composites production represent the usual applications of this technique, which allows surfaces of complex geometry to be uniformly coated. 

Fig. 1.2. Acoustic images of the same 7740/SiC glass matrix composite as in Fig. 1.1. (a) Section parallel to the axis of a fibre (b) section perpendicular to the fibre axes ... 

A ceramic matrix composite or CMC is composed of two or more solids, the matrix of which consists of a ceramic material or carbon. The crystalline, ceramic matrix is moulded and/or densified at a temperature of at least 1000 K. To the matrix one ormore solid inorganic substances are added, e.g. in the form of particles or fibres in order to alter the (thermo) mechanical properties of the pure matrix. In the composite s microstructure these additives can still be distinguished by their chemicalcomposition or geometry even after they have undergone a temperature treatment of at least 1000 K. 

The properties of fibre-reinforced composites are for example determined by a) length, diameter, orientation, volume fraction and properties of the fibres, b) the properties of the matrix and c) the nature of the bond between fibre and matrix. The ratio between length and diameter is an important fibre property. A small diameter means that the area is also small and consequently there is less chance of defects occurring in that area and so less chance of the fibre breaking. 

It is well known that the Young s modulus of a composite can be calculated by the rule of mixtures for long-fibre reinforced material. In the case of whiskers, the rule of mixture is also applied to estimate the change of modulus (conventionally, reinforcements are added to improve the stiffness of a material, though for ceramic matrix composites this is not always the primary concern). 

Fibre-reinforced glass/glass-ceramic matrix composites... 

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