CLEAVAGE-LIMITED MAXIMUM STRENGTH OF WORK-HARDENED BCC POLYCRYSTALS

Bcc metals and alloys maintains a non-decaying work-hardening rate up to high plastic strains when deformed monotonically at low temperatures (T less than 0. 3 T//M), especially by axisymmetric elongation (wire drawing). This offers the possibility of production of strong metallic filaments which are tougher than other fiber reinforcing materials. However, bcc metals being prone to cleave, their rising stress-strain curves could be trimmed by brittle failure beyond some point. This paper studies such contingency and shows that two failure modes are possible: a microscopic-type failure, when the flow stress meets the (strain-dependent) tensile cleavage stress and for large strains, a macroscopic-type failure when the critical stress intensity factor (also strain-dependent) is reached for cracks associated with inclusions or for crack-like surface defects.