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). I was wondering if we are missing out on something because it seems such an obvious line of investigation inspite of the difficulties involved in bi-axial fatigue testing of metals.