Thermal shock of ceramic matrix composites

The aim of this chapter is to present an overview of the performance of ceramic matrix composites (CMCs) under conditions of thermal shock, i.e. when they are subjected to sudden changes in temperature during either heating or cooling. 

The description of the thermal shock behaviour of CMCs is given with reference to the thermal shock resistance of monolithic ceramic materials. Monolithic ceramics have greater thermal shock sensitivity than metals and can even suffer catastrophic failure due to thermal shock because of an unfavourable ratio of stiffness and thermal expansion to strength and thermal diffusivity, and their limited plastic deformation. 

The structure of the chapter is as follows the stress field developed in a thermally shocked component is described in Section 15.2 and maximum stresses are identified and quantified. Section 15.3 contains an overview of 

It should be noted that this review concentrates on thermal shock (i.e. a single thermal cycle) and no attempt is made to incorporate and describe the effects of cyclic thermal loading (cyclic thermal shock, thermal shock fatigue, etc.) on the behaviour of CMCs. For information regarding cyclic thermal loading of ceramics and CMCs the reader is advised to consult the extensive review of Case (2002). Additionally, recent studies have shown that laminated ceramic-metal systems (Sherman, 2001) and layered ceramic-structures (Vandeperre etal, 2001) exhibit better resistance to thermal shock compared with monolithic materials. However, such systems are also beyond the scope of this contribution. 

2 Thermal shock of brittle materials the induced stress field 

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The key advantage of ceramic matrix composites is that, when properly designed and manufactured, they have many of the advantages of monolithic ceramics, such as much lower density than high-temperature metals, but are much more durable. That is, CMCs have higher effective fracture toughnesses, so they are less susceptible to failure when subjected to mechanical and thermal shock. As a consequence, it is possible to consider CMCs for applications where they are subjected to moderate tensile loads. However, CMCs are the most complex of all types of composites, and CMC technology is less developed than that of PMCs, MMCs, and CAMCs. 

Many papers investigating the thermal shock behaviors of ceramic matrix composites have been published, and the deeay in flexural strength measured after water quenching has been theoretically attributed to the micro-flaws that appear on the surface of the speeimen (Meng et al., 2009 Zimmermann et al., 2008 Monteverde et al., 2007 Wang et al., 2001 Gong et al., 2003 Hu et al., 2010). Unfortunately, no... 

As discussed previously, ceramic matrix composites were originally developed to overcome the brittleness of monolithic ceramics. Thermal shock, impact and creep resistance can also be improved, making CMCs premium replacement choices for some technical ceramics. Industrial applications such as in automotive gas turbines or advanced cutting tools are already taking advantage of such characteristics. 

Chlup, Z., Dlouhy, I., Boccaccini, A.R. (2001), Fracture toughness of thermally shocked SiC-fibre reinforced glass matrix composite , in Krenkel, W., Naslain, R., Schneider, H. (editors), High Temperature Ceramic Matrix Composites, Wiley, 463-468. 

Kastritseas, C., Smith, P.A., Yeomans, J.A. (2004b), Damage characterisation of thermally-shocked woven fibre-reinforced ceramic matrix composites , Proceedings of the 11th European Conference in Composite Materials (ECCM-11), Rhodes, Greece, Vol. 2. 

Twitty, A., Russell-Floyd, R.S., Cooke, R.G., Harris, B. (1995), Thermal shock resistance of Nextel/sllica-znconla ceramic-matrix composites manufactured by freeze-gelation , J. Eur. Ceram. Soc., 15, 455-461. 

Wang, Y.R., Chou, T.-W. (1991), Thermal shock resistance of laminated ceramic matrix composites , J. Mater. Sci., 26, 2961-2966. 

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