bernd wrote: ↑
Fri Feb 16, 2018 6:46 am
... This mostly due to singularity because of sharp edges. Means the connection is still ok. But at some point it is no more ok because than there are really yielding areas. The question is how to distinguish brtween both.
Further to my earlier response and specifically on the question of growing/spreading plastic zones:
That is where an elastic-plastic collapse analysis will give you the answer. The plasticity card in Calculix and some other programs allows you to push redundant structures beyond the point of first yielding. In areas where plasticity occurs, stresses in integration points remain on the yield surface, but the stress components in those points can still change due to movement of the stress state in a point along the yield surface or due to hardening (shift or expansion of the yield surface).
In fact, what I hope to get to with FreeCAD in the future is to analyze structural response from first yield to full plastic collapse. This is what I programmed 30 years ago in a program called Plaxis (see Google) and I am keen to get it done again in the FOSS environment. In addition to an elasto-plastic material model (as already available in CalculiX) it requires automatic scaling of load steps and arc length control (mixed load/displacement control) at limit points. This isn't too hard to program but requires full access to the code (which, having done most of my work in Fortran, I find very tough). PS: on the Calculix page Guido announced a long time ago that he is working on a Riks procedure (= arc length control), but I don't see that back in the code.
Sorry for the long response, but this is a main area of interest for me.