Failure Analysis of Ceramic Materials

The general principles involved in the failure analysis of ceramic materials are similar to the failure analysis of metals and alloys. Because of the brittle behavior of ceramic materials, failure may result in many pieces of the sample, which have to be reassembled in order to obtain information on the form of loading and the point of fracture initiation. The utmost care should be exercised in the reassembly of the fractured pieces so that the features of the fracture are preserved. 

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. 

A crack in a ceramic material upon initiation may accelerate and interact with microstructure, stress field and the generated acoustic vibrations. These interactions may lead to some fractographic features such as fracture mirror, hackle or river patterns and Wallner lines. 

The first and foremost step in failure analysis of ceramics consists of identifying the fracture origin and the type of cracking, which throws light on the type of failure such as failure due to impact, residual stress combined with load, thermal shock, improper machining, oxidation and corrosion. This is aided by micro- and macrofracto-graphy, examination of microstructure by SEM, chemical analysis and metallographic examination. 

ISO 7539, Corrosion of Metals and Alloys-Stress Corrosion Testing, International Organization for Standardization, Geneva, Switzerland, 1989. 

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