Microstructure fibre

Cordeiro CMB, de Matos CJS, dos Santos EM, Bozolan A, Ong JSK, Facincani T, Chesini G, Vaz AR, Brito Cruz CH (2007) Towards practical liquid and gas sensing with photonic crystal fibres side access to the fibre microstructure and single-mode liquid-core fibre. Meas Sci Technol 18 3075-3081... 

Oksman K, Mathew AP, Langstrom R, Nystrom B, Joseph K (2009) The influence of fibre microstructure on fibre breakage and mechanical properties of natural fibre reinforced polypropylene. Compos Sci Technol 69 1847-1853... 

In a Hierarchical Fibre Microstructure, Molecules That Have Melted Can... 

The complexity and hierarchy of natural fibre microstructures can allow a variety of simultaneous microstructural changes to accompany mechanical deformation. 

Scanning electron microscopy (SEM) has been used to characterize the physical and chemical interaction of fibres in FRC, as well as to address the durability of fibres. Microstructural analysis provides information on the corrosion of fibres, deposits of Portlandite surrounding fibres and the interaction between fibres and matrix (Purnell et al., 2000). Other techniques may be used as alternative to SEM. Uygunoglu (2008) has shown that polarizing microscopy is a suitable technique to assess the bond characteristics of steel fibres in SFRC, which is also related to durability of the composite. 

This variation in the mechanical properties is due to the fibre microstructure. There are two different structures (so-called allotropes ) of carbon The diamond structure, shown in figure 1.13, only forms at high temperatures and pressures and is in fact metastable at room temperature. The stable conformation of carbon is graphite. In graphite, the carbon atoms are ordered in a... 

Fig. 26.2. The microstructure of wood. Woods ore foams of relative densities between 0.07 and 0.5, with cell walls which ore fibre-reinforced. The properties ore very anisotropic, partly because of the cell shape and partly because the cell-wall fibres ore aligned near the axial direction.

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. 

Ceramic oxide fibres, both continuous and discontinuous, have been commercially available since the 1970s, and processing and microstructure control are very important in obtaining the desired properties. Among the desirable characteristics in any ceramic fibre for structural applications are ... 

The Nicalon fibre (10-20 pm) available commercially consists of a mixture of P-SiC free carbon and Si02 [28], The properties of Nicalon start to degrade above about 600°C because of the thermodynamic instability of the composition and microstructure. Ceramic-grade Nicalon fibres, designated the NL series, having low oxygen content are also available. 

Unlike fibre- or whisker-reinforced composites, particulate composites have the advantage of being compatible with conventional powder processing, and in many cases can be pressurelessly sintered. As with other ceramic microstructures, a myriad of other ingenious fabrication routes have also been reported, but these are too numerous and system-specific to describe here. This section merely outlines the main points of powder processing where the production of composites in chemically compatible systems (i.e. those in which the components do not react chemically with one another) differs from that of monolithic ceramics. 

Kumar, A. and Knowles, K.M., (1996a), Microstructure-property relationships of SiC fibre-reinforced magnesium aluminosilicates - I. Microstructural characterisation , Acta Mater., 44 (7), 2901-2921. 

The relative magnitudes of the Tg values in the two-phase region should be related to the development of microstructure in mesophase pitch, as discussed earlier. Tg will also be a useful parameter in defining the maximum temperature at which fibres can be oxidized without molecular motion causing some decrease in extent of preferred orientation. 

The microstructure of all mouldings was characterised by determining fibre content (weight and volume fraction), average fibre dimensions (diameter and length), fibre length distribution and fibre orientation distribution. 

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