crack sensitivity
thermal shock

Crack Sensitivity 1

strength vs length of crackIn this module we will look at the brittle fracture of ceramics and the statistics of ceramic strength.

We have seen from fracture mechanics that the fracture strength of ceramics is dependent on the largest crack or flaw in the specimen. This means that for any given material, different specimens tested will have variation in the measured strength, according to the length of the largest crack present.

The design strength of a ceramic is determined by its fracture toughness and the cracks that it contains. As we have seen in the fracture tutorial, the design stress is given by:


where KIc = fracture toughness, Y = a dimensionless constant, σ = applied stress, a = length of surface crack or half the length of an internal crack.
This equation is used to determine the longest crack allowed in a part for a given load, or the maximum load a part can withstand if it contains a crack of size a.

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