Symmetry constraint

[sigurd.naess]

Hi!

My model shows large difference in results when using symmetric constraints compared to whole model. My symmetric model fails at 99,7%. What can cause this difference? i'm I applying symmetric constraints wrong?

I have constrained my symetric model in the direction of the global coordinate system 

Fix constraints (red area), flange is loaded as indicated by blue arrows (using a force)

Non-linear analysis, E = 200GPa, E_tan = 0, simga_y = 550MPa, sigma_u = 750MPa

[John_Holtz · Accepted solution]

Hi @sigurd.naess 

The mesh is different in the two models, and a nonlinear analysis is sensitive to the mesh. 

Try using a different value for E_tan (which I think is your tangent modulus). Values of 0 can lead to stability problems. For example, a bar with 1 mm^2 cross section cannot support a 1 N load of the material properties say that it is perfectly plastic after it yields at 0.5 MPa. There is no strain value on that stress-strain curve that results in a stress of 1 MPa! Your model is obviously more complex, but mathematically something similar could be occurring.

Another option to try is to use more than 5 increments. That might be applying too much load in one step. Try 25 or 50 increments.