Competition mechanism of brittle-ductile transition of metals under tensile condition

An analytical approach to the brittle-ductile transition temperature (BDTT) of metals under tensile condition has been carried out. It is assumed that a competition between the crack extension and the dislocation source operation, which correspond to the brittle fracture and the ductile fracture respectively, occurs in front of the crack tip. In this way, the BDTT turns out to be a function of the grain size do and the strain rate r by energy balance condition. The BDTT increases with increasing grain size and strain rate. It is concluded that the temperature dependence of the brittle-ductile transition (BDT) probably arises more from the crack extension rather than from the crack nucleation. Based on the calculation, not only has the BDTT of metals under tensile condition been obtained, but also the traditional phenomenological theory has been explained.