Model Sensitivity to Key Parameters

Subcritical Crack Growth Creep-Controlled Crack Growth 

Of the three parameters, a is the most difficult to estimate and is perhaps the least certain to estimate. The estimated influence of hardness a on crack growth rate is shown in Fig. 6.17, and reflects the effect of local strain s ahead of the crack tip. Examination of Fig. 6.17 suggests that a 10% reduction in a from 2010 to about 1800 MPa could conform the creep crack growth rate model to the experimental data. 

Because crack-tip strain increases with K, a is expected to increase (see Fig. 6.11) commensurately and to alter crack growth response. Its potential influences have been estimated by Yin et al [3], and are shown as dashed curves in Figs. 6.13,6.14 and 6.17 (using the revised data). Even with this weak dependence of a on K, the resulting influence in the lower K region is quite large. Further 

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