Hey,
is it wrong to use 8-node elements in buckling/postbuckling analysis? Riks' analysis are giving me some strange results when I use 8-node elements. I've used 420 as yield stress, but von Mises stress exeeds this.
I'm not sure why it's strange if the stresses exceed yield. Check your results with a hand calculation if possible to get a 'feel' of what your results should be.
Impossible to do hand calculations as the geometry is very complex. Principal stresses can exeed yielding stress, but I thought that max von Mises should be yield stress or below. I'm not sure though.
It's probably because the stresses at the integration points are at yield, but extrapolating to the surface nodes will give you stresses apparently above yield.