Ceramic crack branching

Crack branching is a common feature in failure of ceramic components. Cracks branch at a critical velocity, which is of the order of half the speed of sound in the specific glass under study. The acceleration of crack initiation to the critical velocity depends on the energy dissipation available from the release of stored energy. The energy source can be applied stress, prestressing or residual stress. 

H. P. Kirchner, The Strain Intensity Criterion for Crack Branching in Ceramics, Eng. FracL Mech 10 283-288(1978). 

J. C. Conway Jr, and J. J. Mecholsky Jr, Use of Crack Branching Data for Measuring Near-Surface Residual Stresses in Tempered Glass, ). Am. Ceram. Soc., 72 1584-1587 (1989). 

Toughening in fiber composites can involve the above mechanisms for particulate composites, especially microcracking, crack deflection, and crack branching. Load transfer can also be important, however, it appears to be less essential for ceramic composites than most other composites The one factor that has now been quite well established as central to the... 

Again, the above crack kinking and branching criteria are limited to isotropic homogeneous material, which for all practical purposes will include particulate/whisker-filled ceramic matrix composites. No equivalent criterion exists for orthotropic/inhomogeneous material. Limited experimental results show that self-similar crack extension is a rare phenomenon in fracture of fiber-reinforced ceramic matrix composites and thus the kinking and branching criterion, if developed, must necessarily be a three-dimensional one. 

The key elements of the numerical scheme used in this study are its ability to incorporate the granular microstructure of the ceramic material, to simulate the spontaneous initiation, propagation and branching of intergranular cracks and subsequent fragmentation of the body, to account for inertial and finite kinematics effects and to capture the complex contact events taking place between the fragments. 

Crack shielding in non-transforming ceramics occurs mainly by bridging, branching and deviation and by friction of the crack interfaces. The typical pattern... 

Upon reaching its critical velocity, the crack begins to branch—that is, the crack surface changes propagation direction. At this time there is a roughening of the crack interface on a microscopic scale and the formation of two more surface features—misf and hackle these are also noted in Figmes 12.28 and 12.29. The mist is a faint annular region just outside the mirror it is often not discernible for polycrystalline ceramic... 

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