Boundary conditions problem


I am currently working on the numerical modeling of shear tests under constant normal stress.

In the phase of normal stress application, I am using both ‘block insitu stress’ command and ‘block edge apply stress’ command on the top edge, while the bottom and lateral edges of the sample are fixed in the Y and X direction respectively by using the ‘block gridpoint apply velocity-x or velocity-y 0’.

The application of the block insitu stress command affects the whole specimen (including boundaries), and thus it cancels the application of boundary conditions defined in term of velocities. This problem is causing the specimen to fall gradually with the application of these YY-stresses and thus the model will never converge.

Please note that I have tried to apply these boundary conditions before and after the application of the normal stresses and I have encountered the same problem in both cases.

I would like to have suggestions for solving this problem.
Thank you in advance.

Can you apply the stress in the form of force or velocity and see if it is solving the issue?

1 Like

The block Insitu stress command has no effect on the boundaries.

The block edge apply and block gridpoint apply commands used to apply boundary conditions are order dependent. Any command that applies boundary stresses affects all degrees of freedom. This will remove any previous velocity boundary condition at the gridpoints in the range. Therefor any velocity boundary conditions applied to the same location as a stress must come after the stress command.

1 Like

Thank you for the support.