Ceramic fibres strength

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. 

Tiles and slabs incorporating ceramic fibres offer the advantage of reduced thickness in conjunction with equally good heat-insulating capacity, but they suffer from the drawback of limited strength, so that they can suitably be installed only in relatively small kilns (up to about 3.6 m diameter) and in the static parts of... 

Polymeric/ceramic fibre composite foam Superior compressive strength Potentially harmful solvent residues... 

Various types of fibres could be used in making filter fabrics they include glass fibres, synthehc fibres, ceUulosic fibres (eg, natural wood pulp fibres, viscose fibres, and Lyo-ceU fibres), wool fibres, metal fibres, ceramic fibres, high-performance polymer fibres (eg, inherenfly fire-resistant fibres, chemical resistance fibres, high-strength, and high-modulus fibres), microfibers, and nanofibers. 

Although the uses of ceramic fibres in composite structures lie mainly in ceramic-matrix and metal-matrix composites, where their outstanding chemical and thermal resistance are important, there are a few applications in organic polymers. Their relevant properties are low thermal expansion, low electrical conductivity, low dielectric constant, high stiffness, good compressive strength, and in most cases complete resistance to combustion. On the other hand they are very brittle, hard to process, and mostly considerably more expensive than carbon and para-aramid fibres. They have, for example, been used in hybrid structures with carbon and para-aramid and in electronic circuit boards. The fibres available or potentially available include alumina, combinations of alumina with... 

Several types of continuous ceramic fibres are used here. Fibres made of -type glass s ( 2. Tradition continued. The silica tradition) in composites used for constmction of boats, carbon fibres (Fig. 3.12) in composites used for aviation and sports equipment. Materials other than the continuous fibres can also be applied. Namely, particles where at least one dimension is <100 nm, like clay minerals ( 2. The tradition continued. The clay tradition), carbon nanombes and graphenes (—> 5. Unusual ceramic dielectrics and conductors). Due to a high ratio of length to thickness such fillers are in contact with the polymer matrix over a large area. Therefore, their effect on strength and fracture toughness—can be observed even with a low-volume fractions of fillers (firom 0.5 to 15 %wt). Due to the dimensions of these fillers, these composites are often referred to as nanocomposites. 

Figure 3.4 Strength for glass, aramid, polyethylene, carbon and ceramic fibres.

This chapter is concerned with continuous ceramic fibres derived from organosilicon polymers, and does not cover precursors to oxide ceramics. It should be noted that effective reinforcement of ceramic matrices can be achieved with whiskers and certain particulate materials, as well as continuous fibres, but these materials are not usually made from polymer precursors and fall outside the scope of this chapter. Apart from reinforcement of ceramics, continuous ceramic fibres have considerable potential for reinforcement of light alloys when enhanced strength and modulus is required at elevated temperature. There is also much interest in the development of plastic matrix... 

The compressive strength of composites is less than that in tension. Tills is because the fibres buckle or, more precisely, they kink - a sort of co-operative buckling, shown in Fig. 25.5. So wliile brittle ceramics are best in compression, composites are best in tension. 

Stmcture-property relations usually have a qualitative character (words, causal relations) and can be expressed as if-then clauses by this is an existing property, then it is caused by this type of stmcture or Hf this is the existing stracture, then probably this property can be expected . Stmcture-property relations at the same scale (horizontally) were not found all relations were links between two different (meso-) levels. Stmcture-property relations are different for the different tasks, and even within the same domain (e.g. ceramics) may well be different when the type of requirements is different (e.g. unbreakable versus resistant to certain chemicals). The relations will be specific for specific stmctures and specific properties, e.g. the strength of a jacket, a set of mats, one mat, a cluster of fibres, or one fibre. 

Fibres are added to a plastic or metal matrix, mainly to increase the strength of the material. In case of a ceramic matrix this is done to increase the fracture toughness of the brittle matrix. 

The impact of thermal shock on the properties of a ceramic or a CMC is assessed by means of both destructive and non-destructive testing methods. Flexural or tensile (mainly for CMCs) tests of suitably-sized thermally shocked specimens are usually employed to measure retained mechanical properties as a function of the temperature difference. The temperature differential for which a significant drop in property values is observed is the A A- For monolithic ceramics and particle- or whisker-reinforced CMCs the property under investigation is usually strength, whereas in fibre-reinforced CMCs a drop in Young s modulus is usually a better indication of the onset of damage. 

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