Thermal shock


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Thermal shock - short version

The frature of a brittle material as a result of stresses that are introduced by a rapid temperature change.



Thermal shock - long version

Thermal shock is the name given to cracking as a result of rapid temperature change. Glass and ceramic objects are particularly vulnerable to this form of failure, due to their low toughness, low thermal conductivity, and high thermal expansion coefficients. However, they are used in many high temperature applications due to their high melting point.

Thermal shock occurs when a thermal gradient causes different parts of an object to expand by different amounts. This differential expansion can be understood in terms of stress or of strain, equivalently. At some point, this stress overcomes the strength of the material, causing a crack to form. If nothing stops this crack from propagating through the material, it will cause the object's structure to fail. Thermal shock can be prevented by:

1. Reducing the thermal gradient seen by the object, by

* changing its temperature more slowly

* increasing the material's thermal conductivity

2. Reducing the material's coefficient of thermal expansion

3. Increasing its strength

4. Decreasing its Young's modulus

5. Increasing its toughness, by * crack tip blunting, i.e., plasticity or phase transformation * crack deflection



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