Fracture Resistance of Ceramics

Ceramics Science and Technology Volume 2 Properties. Edited by Ralf Riedel and I-Wei Chen Copyright 2010 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 978-3-527-31156-9 

This stress concentration explanation, however, has a number of factors which are not consistent with the observation of the effect of cracks upon strength of materials. 

(1) states that the stress at point C is dependent upon the shape of the crack, and not its length however, this is inconsistent with observations that long cracks are more likely to lead to premature failure than short cracks. Second, the insertion of a value Q consistent with the radius of a crack tip, which is believed to be in the order of a few atomic spacings, would result in failure stress values far lower than those which are observed in components containing defects. Hence, the concept of a stress concentration factor alone does not explain the deleterious effect of defects upon the strength of a material. 

This issue was addressed by A.A. Griffith, whose theory is used today by engineers and scientists to determine the strength of materials containing defects [3]. This theory established an energy criterion for fracture which states that crack growth occurs when  

Energy deliverable by a system Energy required to form an additional crack. 

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This work has been supported by METI, Japan, as part of the international standardization project of test methods for rolling contact fatigue and fracture resistance of ceramics for ball bearings. 

G. Gogotsi, S. Mudrik, V. Galenko, Evaluation of Fracture Resistance of Ceramics Edge Fracture Tests, Ceram. Int, 33,315-320 (2007). 

G. D. Quinn, A. A. Giuseppetti, K. M. Hofhnan, J. B. Quirttt, Edge Chip Fracture Resistance of Ceramic and Composite Materials, Presented at the 37 ICACC, American Ceramics Society, Daytona Beach, FL, Jan. 2013. 

A partial answer to the first question has been provided by a theoretical treatment (1,2) that examines the conditions under which a matrix crack will deflect along the iaterface betweea the matrix and the reinforcement. This fracture—mechanics analysis links the condition for crack deflection to both the relative fracture resistance of the iaterface and the bridge and to the relative elastic mismatch between the reinforcement and the matrix. The calculations iadicate that, for any elastic mismatch, iaterface failure will occur whea the fracture resistance of the bridge is at least four times greater than that of the iaterface. For specific degrees of elastic mismatch, this coaditioa can be a conservative lower estimate. This condition provides a guide for iaterfacial desiga of ceramic matrix composites. 

Becher PF, Hwang SL, Lin HT, Ticgs TN (1994) Microstructural contributions to the fracture resistance of silicon nitride ceramics. In Hoffmann MJ, Petzow G (eds) Tailoring of Mechanical Properties of Si3N4 Ceramics, NATO ASI Ser E Vol. 276, Kluwer Academic Publishers, Dordrecht, p 87... 

Kuebler, J., Fracture toughness of ceramics using the SEVNB method from a preliminary study to a standard test method, in Fracture Resistance Testing of Monolithic and Composite Brittle Materials, ASTM STP 1409, ed. J.A. Salem, M.G. Jenkins and G.D. Quinn, ASTM, West Conshohocken, PA, pp. 93-106, January 2002. 

PT. Becher, S.L. Hwang, H.T. Lin, T.N. Tiegs, Microstructural contributions to the fracture resistance of silicon nitride ceramics, pp. 87-100 in Tailoring of mechanical properties of Si3N4 ceramics. Edited by M.J. Hoffmann and G. Petzow, Kluwer Academic Publidiers, Dordrecht, 1994... 

Becher, P.F., Hwang, S.L., Lin, H.T., and Tiegs, T.N. (1994) Microstructural Contribution to the Fracture Resistance of Silicon Nitride Ceramics, in Tailoring of Mechanical Properties of Si3N4 Ceramics (eds M.J. HofBnarm and G. Petzow), Kluwer Academic Publishers, Dordrecht, The Netherlands, pp. 87-100. 

Biomaterials such as teeth, bone and mollusk shell exhibit excellent strength and fracture resistance their mechanical strength is superior to that of many bulk ceramics and synthetic composites. The fracture resistance of these biological materials is particularly striking in light of the fact that the major constituent phase... 

The thermal shock fracture behavior of ceramics has been investigated using traditional testing methods such as the water quench in which the critical temperature difference, where samples are subjected to severe damage, is used as the thermal shock resistance. Recently, new experimental methods are proposed and applied to the investigation of macroscopic crack propagation process during thermal shock fracture, based on fracture mechanics. ... 

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