Effect of loading orientation on fatigue behaviour in severely notched round bars under non-zero mean stress bending-torsion

This paper studies the effect of different loading orientations on fatigue behaviour in severely notched round bars under pulsating in-phase combined bending-torsion loading. Bending moments are applied in three different planes with respect to the notch root considering two bending moment to torsion moment ratios. Complementary, beach-marking tests are also performed for different loading scenarios to evaluate the crack shape changes during the crack growth. After fatigue testing, specimen surfaces are examined by scanning electron microscopy to identify the main failure micro-mechanisms. Fatigue life is predicted via the Coffin-Manson model, and the notch effect is evaluated using the Equivalent Strain Energy Density concept. Overall, experimental and predicted lives are very reasonably correlated. Furthermore, initiation sites, initiation angles and surface crack paths are successfully predicted from the principal stress field at the notch.