Hi all,

I'm opening this thread in order to have some clarification about a non linear geometry analysis I'm running on APDL. The model is very simple, it's characterized by a 1500x3000 mm grid with a 40x40 mm pitch of beam188 elements, with translational constraints on the external borders and borders every 1000 mm, so that we have along the 1500 dimension 4 borders constrained, while 2 borders along 3000 dimension all constrained. I used a circular section with 2 mm radius for the beam188 elements. The load applied is at the center of my grid, on a 200x200 mm area, with a value of 1400 N, equally distributed. Since my model undergoes large displacement, I had to switch the analysis to a non-linear geometry solution. I used, as non linear material model, the BIHP (bilinear isotropic hardening plasticity) with a value of 235 MPa as YS and 2000 as Et. The isotropic part would be the classical of a steel, so that Ex would be equal to 210000 MPa and poisson's ratio of 0.3. Now the things I noticed running different analysis are really strange. Indeed, with the same load condition and Et, if I change the value of YS (let's say, 235 then 300 then 400 and so on), the von mises and equivalent plastic stress that I have as output will increase as well. This is a thing that I can't explain, since the load I'm applying every time is the same, what I'm changing are the mechanical properties of my plasticity field. If during my first analysis, with YS at 235 MPa, I have a VM stress of 270 MPa, I don't expect it to increase during my second run, with a YS of 300 MPa, to about 340 MPa! The displacements are the same during the two runs, what change are the stress and strains, that's why I can't make a good correlation between my FE model and what I'm expecting to happen. Could someone give me an explanation about it? Thanks in advance for any replies!