Sub-critical crack growth parameters

To include the effect of sub-critical crack growth into design, it is necessary to determine experimentally the values of B and n, the sub-critical crack growth parameters. These parameters define the behavior of a material in a given active environment. Three types of approach are commonly used for this purpose and these will be discussed below. 

Determination of sub-critical crack growth parameters by in-situ observation of indentation cracks, J. Am. Ceram. Soc., 78 [8] (1995) 2122-8. 

Name two approaches for determining the sub-critical crack growth parameters. 

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