Discussion Forum

Yes, without constraints there is an infinite number of solutions. You need to remove all rigid body motions (6 in 3D, 3 in 2D). In the current version, 5.3, this can be achieved using a "Rigid Motion Suppression" node, but since you are using 4.3a you wil need to do it the old fashion way, namely by imposing displacements at some points (or boundaries if you have symmetries that allow it).

Best,

Jeff

thanks for the prompt reply.

As you suggested if impose the displacement constraints at some points, I will get corresponding reactions at those location. This will give me deviated answer from the actual one.

My all the points in the cube (except th points on which force is applied) should ideally have all 6 DOF's under the action of applied force. How can I simulate this tensile test in such cases?

Unless you are talking about a shell, in 3D, each node only has 3 degrees of freedom associated with it: one displacement per axis. Shells do have 6 degrees of freedom at each node.

And again, if you do not apply any constraints, your mathematical problem is singular: it has an infinite number of solutions. Physically speaking, an unconstrained object is "floating in outer space": an infinetisimal additional force would make it accelerate away to infinity - and that is not representative of the tensile test you are trying to simulate.

How you choose the constraints to apply depends on the physical situation you are trying to simulate, so it's hard for someone who is not intimately familiar with your physical set up to make recommendations. Ultimately, you need to ask yourself "Which one of the infinite number of solutions do I want the software to find?". The answer to that question may be something like "the one where point A does not move and point B does not move in the y direction and point C does not move in the x direction and point D does not move in the z direction", or it could be "the one that respects symmetry about the x-y plane and where point E does not move", etc. Your answer to that question will dictate what constraints you need to impose.

Jeff

An additional comment:

If you apply correct constraints for suppression of the rigid body modes, there will be no reaction forces, since your loads are self-equilibrating.

Henrik

Hey, Thank you guys.

I did apply constraint and was able to get my solution which is in correlation with theoretical results.

Thanks again for help.

Dear Ganesh, I have exactly your problem. How did you define the fixed constraints? Could you please help me..

Many thanks, Sherry

Apply force on one face and apply contraint on its opposite face, this should work. I did the same

Thank you very much.