Determination of Subcritical Crack Growth Threshold in Ceramics with Indentation Flaws
A technique for determining high temperature subcritical crack growth threshold in ceramics with indentation flaws is presented. This technique requires prior knowledge of the residual stress field about the indentation. Detailed analysis shows that the residual stress is the only driving force for crack growth of indentation flaws in absence of any applied stress. Under certain conditions, it can cause a spontaneous extension or healing of the indentation flaw. Making the duration from just indented to measurement of crack dimension long enough, an equilibrium configuration for the indentation flaw system may be obtained and the threshold can be calculated with parameters which are used to characterize this configuration. This technique is then applied to a pressureless sintered Si3N4. It is shown that this technique may be a simple and reliable method for the determination of subcritical crack growth threshold of ceramics at elevated temperatures.
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