Multiple steps and loads with different boundary conditions

[kdanas]

Hi,

I am using FEAP 8.3.

I am trying to carry out a FINITE STRAIN calculation with two steps. In each step not only the amplitude
of the load changes (in that case I can work it out with the Load groups) but the boundary
conditions (i.e., BOUN, ... restrained and unrestrained) change.

For instance, suppose that :

1) step 1, I block node 1, dof:1 and want zero force (unblocked) dof:2
and
2) Step 2, I want to release dof:1 (zero force) of node 1 and block dof:2 of node 1
but re-starting my calculation from where it was left.

That for instance is required in complex, non-proportional loading paths (like first, tension and then torsion)

How could I do this in FEAP? I am currently working on a new magneto-mechanical element
and I need to carry out first a mechanical loading and then a magnetic loading each time at different
nodes.

Thank you in advance.
Kostas

[FEAP_Admin]

This can be done by solving the problem for the first step.  Then re-entering the mesh phase and changing the boundary conditions.  Then continuing to solve for the second step.  (I will try to make a simple example for you and post it.)

Alternately there is a way perform this for simple 1-D and 2-D problems from the plot phase using the commands Plot> pboundary and Plot> pdisplacement (please see the user manual appendix for the plot commands).

[FEAP_Admin]

Here is an example.  If you run the file it will solve the problem and plot it with the first set of boundary conditions.  (load is the green arrow, support reactions are the yellow arrows, red lines are the fixed directions).  If you now type QUIT at the macro prompt and hit the return key twice, it will exit interactive mode, change the boundary conditions, resolve the problem, and re-plot the solution.  Note that the boundary condition in the lower left corner has changed and the reaction vector had appropriately changed directions.

When doing this it is important to understand how FEAP expects to see its data.  When you have

batch
  mesh
end

FEAP looks for mesh commands to be placed immediately after the 'end' associated with the batch block.  It will read anything it finds as a mesh command up until the time that it reads an 'end'