Hi there, i´m quite new to LS-DYNA but i hope to find some help here.
I´m trying to simulate triaxial tests to verify against real test results on soil using MAT_207_SANISAND.
My model consists of just one solid element (so equal stress and strain throughout) with lengths of 1x1x1. To apply an inital stress of 100 kPa to chosen surfaces of my model, i generated segments using SET_SEGMENT and then applied it with LOAD_SEGMENT_SET, but to no avail. The model just doesn´t get compressed by the load at all. I checked the AT, which is correctly set at 0.0. The load curve also gives the correct load-time-input. The example given in the keyword manual for LOAD_SEGMENT almost exactly replicates my situation, and i couldn´t see where i differ from the example except for node IDs. I´m out of ideas at this point.
But if i apply a prescribed motion from the top surface to compress the model by 20% alone (which would be the second part of load in my model after applying the inital stress), it works just fine and displacement and stress are calculated.
So, if someone has an idea where the problem might come from, i would really appreciate your help!
Sounds like you are over-constraining your model. I assume you are just trying to apply load to the top of your element and constrain the bottom? You should be able to use *Load_segment, select only that top segment since you are only simulating one element, and then constrain the bottom nodes using *boundary_spc_set and only constrain in your vertical direction (set DOFZ = 1 if z is vertical). You want to make sure your element can expand outwards if you material is incompressible. I'm not familiar with the material you mentioned.