A DISLOCATION DYNAMICAL THEORY OF THE DUCTILE-TO-BRITTLE TRANSITION

A mesoscopic dislocation dynamics approach is used to describe subcritical crack growth due to transgranular cleavage of semi-brittle materials. From an analysis of the concurrent effects of (i) crack tip dislocation emission, (ii) crack shielding and (iii) propagation of the plastic zone into unyielded material which is applied to a crack loaded in mode III, a novel criterion for the ability of a material to sustain stable crack growth is derived. This yields an analytical expression for the ductile-to-brittle transition temperature as a function of macroscopic material parameters and loading conditions. As the discussion of the role of (i) irradiation ageing, (ii) dynamic strain ageing, (iii) cold working and (iv) impact loading on the ductile vs brittle materials' response demonstrates, the results are in good qualitative and quantitative agreement with experimental observations.