Frank-Read sources and the yield of anisotropic cubic crystals

Frank-Read sources are among the most important mechanisms of dislocation multiplication,

and their operation signals the onset of yield in crystals. We show that the critical

stress required to initiate dislocation production falls dramatically at high elastic

anisotropy, irrespective of the mean shear modulus. We hence predict the yield stress of

crystals to fall dramatically as their anisotropy increases. This behaviour is consistent

with the severe plastic softening observed in alpha-iron and ferritic steels as the

alpha − gamma martensitic phase transition is approached, a temperature regime of crucial

importance for structural steels designed for future nuclear applications.