Cyclic response and early damage evolution in multiaxial cyclic loading of 316L austenitic steel

Abstract

Cyclic stress-strain response and fatigue damage character has been investigated in austenitic stainless steel 316L. Hollow cylindrical specimens were cyclically deformed in torsion and combined axial-torsion under constant strain rate condition and different constant strain and shear strain amplitudes. In-phase and 90° out-of-phase cyclic straining was applied and the stress and plastic strain response has been recorded. Cyclic hardening/softening curves were assessed and plotted using equivalent stress and strain. Long-term cyclic hardening followed initial cyclic softening in case of high strain amplitudes. Cyclic hardening was proved to be connected with the formation of strain induced martensite. Cyclic stress-strain curves were determined. The study of the surface damage in fractured specimens identified the types and directions of principal cracks. FIB cutting revealed the mechanisms of the early fatigue damage leading to production of persistent slip markings consisting of extrusions and intrusions. Fatigue crack initiated typically from the tip of intrusions in all straining conditions.