Triaxial ceramic

The relative amount of each of the three components in the green unsintered shaped precursor product determines the properties and hence the possible applications of the end product. The composition of such triaxial ceramics can be seen in Figure 4.18. 

Porcelain is a typical representative of fine ceramics made from three principal raw materials kaolin (clay), quartz and feldspar (the so-called triaxial bodies). These raw materials in suitable proportion are ground and mixed with water in ball mills and homogenized in blungers. The entire procedure can be illustrated by the following flow sheet which is typical for the manufacture of traditional fine ceramics ... 

Porcelain is a non-porous, white and partially translucent ceramic material of a triaxial composition. It was known in China at the beginning of the present era and was developed in Europe only in the 18th century. High-quality kaolin is a necessary condition for the production of porcelain. Manufacture of porcelain has therefore developed in countries with deposits of suitable kaolin. 

In a separate investigation [5], we have examined the fracture behavior pertinent to the ceramic/metal FGM system concerned, and proposed a criterion for the initiation of cracking in the brittle ceramic phase. Basically, we consider a stress triaxiality /S ... 

Chapters 8 and 9 consider the mechanical properties of rubber- and ceramic-particle toughened-epoxy materials. The importance of rubber cavitation is highlighted in Chapter 8. It is well known that this mechanism can relieve the high degree of triaxiality at a crack tip in the material and enable subsequent plastic hole growth of the epoxy resin, which is a major toughening mechanism. We return to rigid particles in Chapter 9, which examines their use to increase the thermal shock resistance of epoxy resins. 

Traditional ceramics are mainly made from mixtures of clays, silica (often extracted as flint) and feldspars (especially K2Al2Si60i6 and Na2Al2-SieOie). Low-quality structural products such as bricks and pipes are made directly from the appropriate clay. Higher-quality ceramics such as porcelain are made from carefully controlled amounts of specific clay, flint and feldspar. The use of these three major components has led to the name triaxial whitewares for these materials. 

FIGURE 2.4 The flow of ceramic history illustrates the mainstreams of earthenware, terra cotta, and stoneware, of triaxial hard-paste porcelain, of quartz-based bodies, and of tin-glazed ware. Some important shaping and decorative techniques are illustrated, but the diagram is far from complete. 

Zou W, Song M, Wan T, Yan L, Wan K, Triaxially braided C/SiC composites, research and development by the combined process of CVI-FPIP, Niihara K, Nakano K, Sekino T, Yasuda E eds.. Ceramic Society of Japan High Temperature Ceramic Matrix Composites III, Proc 3rd Int Conf, Osaka, Key Eng Mater, 164—165, 213-216, 6-9 Sep 1998. 

Uniaxial and triaxial compression tests of silicon-carbide ceramics under quasistatic loading conditions were performed by Brannon et al. [33]. Their SiC-N specimens were prepared in the form of a right circular cylinder, as is indicated schematically in Fig. 1.43a next to the experimental set-up. 

In many cases, the cleavage strength ac cannot be measured experimentally. For example, body-centred cubic metals only fail by cleavage fracture even at temperatures below the ductile-brittle-transition temperature if the stress state is triaxial. For this reason, it is impossible to measure ac in a tensile test. Ceramics usually fail because a microcrack, already present in the material, propagates and causes failure at a stress below ac (see section 7.3). The tensile strength of a ceramic is thus smaller than its cleavage strength, nn... 

When the ceramic contains more than one phase, each phase will have different thermal expansion coefficients. On heating and cooling, this difference can give rise to thermal stresses at the phase boundaries. These stresses can cause internal cracks. Such a crack is seen in the microstructure of a triaxial whiteware composition, shown in Figure 6.13. 

Microstructure of a triaxial whiteware composition. (From W. D. Kingery et al.. Introduction to Ceramics, 2nd Edn., John Wiley, 1976, pp. 783-812.)... 

K. Dana, S. Das, and K. S. Das, Effect of Substitution of Fly Ash for Quartz in Triaxial Kaolin-Quartz-Feldspar System, Journal of the European Ceramic Society 24, 3169-3175, 2004. 

P.W. Olupot, S. Jonsson and J.K Byaruhanga, Development and Characterisation of Triaxial Electrical Porcelains from Ugandan Ceramic Minerals, Ceramics International 36, 1455-1461, 2010. 

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