Figure 11

The BDT temperature passes through a maximum at an intermediate grain size. For materials or microstructures for which the intersection points of grain boundaries with the crack front is the relevant measure for \(\lambda \), a decrease of grain size results in a decrease of the transition temperature (a). For microstructures for which the mean distance of intrinsic sources is the relevant measure for \(\lambda \), a decrease of grain size results in an increase of the transition temperature (b). In (c), the data from Fig. 1 is discussed against the background of the mean findings of our numerical experiments.