Importance for Material Damage Prognosis and Life Cycle Engineering

5 Importance for Material Damage Prognosis and Life Cycle Engineering 

da/di)sy and (da/dt)py are the rates of crack growth associated with the secondary and primary precipitates, and the areal fraction of precipitates is assumed to be equal to the volume fraction, and is the volume fraction of y at the onset of coarsening (or the transformation from secondary to primary precipitates). Alternatively, the area fraction may be taken to be equal to the 2/3-power of the volume fraction. The possible dependence of sustained-load crack growth rates on y volume fraction, in oxygen at = 50 MPa-m, is shown in Fig. 8.34 [37, 38]. The volume fraction of y precipitates in Waspaloy and the associated trend hne for crack growth rates are estimates, whereas those at the higher volume fractions are supported by data [37,38], 

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