Experimental data showing effect of stress state
While there is a lot of experimental literature available on the effects of stress-state on ductile failure under monotonic loading, corresponding studies on fatigue mostly involves bending and torsion type of combination loading. Unfortunately, such a loading corresponds to one of the principal stresses being negative and therefore not as critical. We could find only two references which show clear effect of biaxial state of stress in a pressurised cylinder subject to additional axial load (Biaxial-tension fatigue of inconel 718, it is a report in UIUC 1989).