Learning Forum

[Zainaba98]

Hi all,

I have a problem manipulating B.C.'s. To explain it, I'll use a simple structure:

1- I have a simple bar with two faces 1 and 2. I need first to displace face 2 in the xoy plane (constant z for face 2) while maintaining face 1 fixed. 

2- Then starting from the resulting configuration in step 1, I need to apply a displacement along z on face 2, while having face 1 FREE now to move in all directions and to rotate around all axes.

[1shan]

I am not clear about what the objective is. You are deforming the body in step 1 and then at the start of step 2 removing all constraints? If that happens the body should come back to its original undeformed position unless there is plastic deformation. You can activate and deactivate constraints at each load step (https://www.youtube.com/watch?v=lrmxV-zWqtQ) but you need some supports to prevent rigid body motion. For example you could proceed in step one as you want and in the second step deactivate the rotational end 1 (but not all), while applying z displacement to end 2
Regards Ishan.

[Zainaba98]

thanks for your reply.
My goal is to displace face 2 in xoy place while face 1 is FIXED then 'BLOCK' the configuration that I get [call it configuration 1].
On configuration1, I want to apply a displacement along z on face 2 while face 1 is FREE.
I tried the way you said (activating and de-activating) but unfortunately it didn't work. The problem is that just as u said, the body goes back to its original undeformed position when I deactivate fixing face 1. That's why I used command APDL to 'block' the body in the deformed position and it worked just fine. The problem is, in step 3 [when I want to displace face 2 in z direction while face 1 is free to move in all directions], it's considering always that face1 is fixed although I have no constraint that says so.

[Zainaba98]

So in short, am trying to do:
1- fix face1 + displace face 2 in xoy plane -> get resultant configuration [configuration 1] (I successfully done)
2- block configuration1 so that body doesn't go back to undeformed position (sucessfully done)
3- displace face 2 in z direction with no constraints on face 1 (unsuccessful because it's considering that face 1 is always fixed though I didn't write such a constraint in step3)

[1shan]

You cant "block " the body without applying constraints. The command you have issued does the same thing - fixes all dofs of the remote point scoped to the end faces (i.e fixes the face). If you want to use the deformed geometry in a stress free state, you simply add another static structural analysis and connect the solution cell to the model cell. You can then perform the second step in the new static structural. But again you will need enough constraints to prevent rigid body motion.
Regards Ishan.

[Zainaba98]

Ok I see your point now, the problem is that I need to take the resulting stresses into consideration in my simulation.