Atomistic models were used to examine how heterogeneities at or near to a crack-tip influenced the barriers to dislocation nucleation. Two simple scenarios were proposed in order to probe spatial and chemical effects. In the first example, the effect of surface steps along the crack front was probed. In the second case, substitutional solutes were introduced upon the emission slip plane at and in front of the crack front. The impact of these heterogeneities was assessed by comparing the activation energy barriers for dislocation nucleation with a crack tip of the same orientation and loading without the heterogeneities present. The impact on the activation energies for emission was shown to be a function of the heterogeneity density and the volume of activation required at a given stress intensity.

The Effect of Heterogeneities on Dislocation Nucleation Barriers from Cracktips in α-Fe. P.A.Gordon, T.Neeraj, M.J.Luton: Modelling and Simulation in Materials Science and Engineering, 2009, 17[2], 025005 (15pp)