I am having the following problem:
I want to model the flattening of a pipe, using solution 601/106. I got some results. My question is:
I have used a plastic material with the stress-strain curve prezented in the Elemental Nodal stress.rar file (stress-strain.jpg). The final value for stress is 490 MPa.
The two archives present the results for a total deformation of 85 mm, that is elemental and element nodal stresses (see the archives with the corresponding names). As you see, values much greater than 490 Mpa are present, although the XTCURVE is set to Not Extended, and I would have expected that values greater that 490 will not be present.
Do I make a mistake?
Stresses are dependent on loads, so if you are getting high stresses your loads are high compared to the laod carrying ability of the part.
In your model, to quickly get a ballpark stress value check the P (load) / A (area) at the critical cross-section. This will only give you a ballpark at this does not account for the fact that as the sides are compressed the critical sections will see some hoop effect from the compression.
Also when comparing elemental vs. nodal results make sure that for elemental results do not compare the average or minimum stresses.
Finally, check the element quality and if necessary use hex elements instead of tet elements.
I am not sure what you mean by: "as long as the stress-strain curve is not extended, in NX, the elements where stress goes beyond the ultimate stress limit are canceled".
Even if you apply a displacement, (representative of compressive load) at the flat faces, at the critical section (curved section) it is not just compression that is causing the high stress.
If this was a flat tube with one end fixed, and apply load on the other end (similar to a column), you will notice that the deflection matches the stress strain curve.