Notch effect on torsional fatigue of austenitic stainless steel: Comparison with low carbon steel

Abstract

Notch effect in austenitic stainless steel under cyclic torsion is quite different depending on the superposition of static tension. In pure torsion, the rubbing of the serrated factory-roof type crack faces delays the crack growth along the notch root. Thus, the lifetime in notched specimen becomes longer than in smooth specimen. However, in cyclic torsion with static tension, the flat crack path and mean tensile stress reduce the influence of the crack face contact. Accordingly, shorter lifetime resulted from higher strain concentration at the notch root. Crack growth in low carbon steel under cyclic torsion is highly affected by the ferrite/pearlite banded microstructure besides the addition of static tension. Because of a small amount of the crack face contact, the reduction of lifetime in notched specimen is revealed irrespective of superposition of static tension.