Dynamic shear band propagation and failure in AISI 4340 steel

Failure of metals and their alloys at high strain-rates is usually preceded by formation of adiabatic shear bands, along which cracks can easily nucleate and rapidly propagate causing fracture. In this study, adiabatic shearing and its effect on fracture behavior of AISI 4340 steel at high compressive strain-rate of about 1.9 × 103 s−1 was investigated. Cracking was initiated by formation of micropores during adiabatic heating and thermal softening along the shear bands. As adiabatic shearing proceeded, the pores coalesced to form clusters of pores. Microcracks that eventually grow and cause shear failure along the adiabatic shear bands are initiated from these clusters of pores.