The fracture behaviour of single-crystal pure iron was studied by four-point bending of pre-cracked specimens at temperatures between 77 and 180 K and strain rates between 4.46 × 10-5 and 4.46 × 10-3 s-1. Fracture behaviour changes from brittle to ductile with increasing temperature. The brittle-ductile transition (BDT) temperature increases with increasing strain rate. The relation between BDT temperature and strain rate follows an Arrhenius relation, giving an activation energy for the BDT of 0.33 eV. Dislocation-dynamics simulations of the crack-tip plasticity and resultant shielding of the crack tip were performed using two different variants of the dislocation velocity/stress/temperature relation. The models predict an explicit BDT, and give a good quantitative fit to the experimental transition temperatures.
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