Ceramic crack propagation

Ceramic composites, which use ceramic fiber or whisker reinforcement in a ceramic matrix, are less susceptible to brittle failure since the reinforcement intercepts, deflects and slows crack propagation. At the same time, the load is transferred from the matrix to the fibers to be distributed more uniformly. These ceramic composites are characterized by low density, generally good thermal stability, and corrosion resistance. 

Uniform microstractuie is cracial to the superior performance of advanced ceramics. In a cerantic material, atoms are held in place by strong chentical bonds that ate impervious to attack by corrosive materials or heat. At the same time, these bonds are not capable of much "give." When a ceramic material is subjected to mechanical stresses, these stresses concentrate at minute imperfections in the microstmcture, initiating a crack. The stresses at the top of the crack exceed the threshold for breaking the adjacent atomic bonds, and the crack propagates throughout the material causing a catastrophic brittle failure of the ceramic body. The rehability of a ceramic component is directly related to the number and type of imperfections in its microstmcture. 

Crack propagation, ceramics, 5 628-630 Crack-resistance behavior... 

Since fibrous monolithic ceramics are intended for use in applications where stresses are primarily generated due to bending, strength and work-of-fracture in flexure are measured to evaluate their basic mechanical properties. In addition, factors determining the manner of crack propagation should be... 

Optical photograph of crack propagation of the fibrous monolithic Si3N4/BN ceramic after flexural testing (adapted from ref. [29]). 

Hasselman, D.P.H. (1969), Unified theory of thermal shock fracture initiation and crack propagation in brittle ceramics , J. Am. Ceram. Soc., 52, 600-604. 

Some reports have cited bridging across the relatively ductile metal particles as mechanisms which contribute to the increase in fracture strength.54 Other reports demonstrate cracks propagating at the metal-ceramic interfaces,... 

Different parameters impose different requirements on ceramic materials depending on whether fracture resistance or crack propagation resistance is of prime importance. The values of the above parameters for a range of ceramic materials are presented in Table 15.1, where the property dependence of thermal shock behaviour can be observed. A variety of other parameters... 

Aveston, J., Cooper, G.A., Kelly, A. (1971), Single and multiple fracture , in The Properties of Fiber Composites, IPC Science Technology Press, Guildford, UK, 15-22 Bahr, H.A., Weiss, H.J., Maschke, H.G., Meissner, F. (1988), Multiple crack propagation in strip caused by thermal shock , Theor. Appl. Fract. Mech., 10, 219-226. Bannister, M.K., Swain, M.V. (1990), Thermal shock of a titanium diboride based composite , Ceram. Int., 16, 77-83... 

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