Interrupted Crack Growth

To ascertain the existence of an OAR ahead of the tip of a growing crack and to determine which elements might be oxidized there, mechanically and chemically based, interrupted crack growth experiments were carried out. The findings from these experiments are summarized below. 

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In the static crack growth experiments reported in this chapter, the time period for the application of the sustained load (before the interruption of the test for crack observations) was also typically smaller than the transition time, tT. This permits the stress intensity factor K to be used as a characterizing parameter for static crack growth. 

However, it is possible that the constant rate of AE activity is interrupted by local peaks of high rate of AE. This is due to the formation of local (internal) delaminations because of interlaminar stresses arising due to the presence of transverse cracks. This is more accentuated in less severe loading conditions. Under severe loading conditions = 80% CTu, R = 0.1) the rate of damage development (delamination growth) is so fast that leads to an overall high rate of AE emission. 

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