Effects of Non-Metallic Inclusions and Mean Stress on Axial and Torsion Very High Cycle Fatigue of SWOSC-V Spring Steel

Inclusion-initiated fracture in high-strength spring steel is studied for axial and torsion very high cycle fatigue (VHCF) loading at load ratios of R = −1, 0.1 0.35. Ultrasonic S-N tests are performed with SWOSC-V featuring intentionally increased numbers sizes non-metallic inclusions. The limit considered the threshold mode I cracks starting internal influence inclusion size Vickers hardness on cyclic strength well predicted Murakami Endo’s area parameter model. In presence similarly sized inclusions, stress biaxiality by a ratio to 0.86. Load sensitivity accounted factor ((1 − R)/2)α, α being 0.41 0.55 loading. VHCF properties under cannot appropriately be deduced from data. contrast loading, defect increases significantly superimposed static mean load, no inclusion-initiated found −1. Size effects gradient effective explain smaller crack initiating inclusions ultrasonic tests.