On the necessity of triaxiality and microstructural orientation to produce anisotropic fracture in cold drawn pearlitic steel: Resembling John Ford's Monument Valley

摘要

This paper studies the notch-induced anisotropic fracture behaviour in progressively cold drawn pearlitic steels. The necessity is emphasized of both stress triaxiality (constraint) and microstructural anisotropy (orientation) to induce anisotropic fracture behaviour in the pearlitic steel wires. A materials science approach to the phenomenon is proposed, so that the strongly anisotropic fracture behaviour of the steels with high level of strain hardening (which exhibit a fracture profile with 90° step) is rationalized on the basis of the markedly oriented pearlitic microstructure of the cold drawn pearlitic steels that influences the operative micromechanism of fracture in this particular case, and a sufficient level of stress triaxiality (constraint) in the notched specimens is required to obtain the aforesaid anisotropic fracture behaviour (associated with cracking/fracture path deflection and mixed mode propagation) and to avoid the otherwise isotropic fracture behaviour appearing for low stress triaxiality (constraint) levels, in spite of the marked microstructural anisotropy (orientation) in the most heavily cold drawn pearlitic steels.