Stress range for fatigue multiaxial loading

[boek]

I am doing a fatigue assessment of a structure under multiaxial loading. The load state for the structure is similar to the one in the picture below. Loads are presumed to be in phase. I am trying to obtain a stress range to estimate the fatigue life using the principal stresses of the FEA.

I am running a linear analysis in ABAQUS using two steps where each vertical component is combined with one horizontal component.

Can I just subtract the stress components for the two cases and then compute the principal stresses from the difference of the stress tensors? If this is the case, is it sufficient to only consider the maximum principal stress or do I need to compute a range according to S[sub]1[/sub]-S[sub]3[/sub]?

This method fails to distinguish between compressive and tensile stresses. Is there a simple approach to compute the stress range to predict the fatigue life for this load state? I do not have access to any software like fe-safe or similar.

 

[rb1957]

superposition of loads is (of course) valid. But that is not superimposing principal stresses.

That's something I hadn't thought about ... we combine loadcasees (by superposition), but then the derived stresses (like principal stress) should be recalculated from the combined element stresses. I wonder if that's how it's done ... I hope so ! just combining things (like principal stress and principal stress angle) would not be right.

"This method fails to distinguish between compressive and tensile stresses." ... yes, but it's easy to filter for positive stress.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.