Bimetallic model issue

[LeoFerrante]

Hello everyone,

I am trying to model a bimetallic element with a current passing through it. It is modeled like a beam fixed on one side and simply supported on the other side and there it has to have a 4MPa closing pressure.

I am using a Matlab code and modeling it with Q8 elements, to achieve the closing pressure I tried different combinations of boundary conditions but I found the same problem with all of them and it is the following:

The reactions in the simple supported side are negative and positive, which do not correlate with the theory of simple supported beams.

In the first place, I believe I was because the "tip" of the bimetallic is trying to no longer be in contact and I started to free these nodes but the problem persists. Even if I select only two nodes, which is most likely to have a line instead of a contact area, there is a considerable negative reaction.
Of course, I made every possible patch test and I made the same model in NX and I got the same results.

The question is, Why is It happening? Why my model does not correlate with reality and what can I do to avoid it?

Using contact to model it is not a solution because I am not allowed to.

 

[SWComposites]

A theoretical simple support is applied only at a single location (node).

 

[ThomasH]

Adding to SWComposites reply.

"Simply supported" can in the case be translated to "free to rotate". Since you have locked three nodes it is not free to rotate. If you lock only one node you can't have both negative and positive reaction. Correct?

 

[LeoFerrante]

Yes, of course. It's not a simply supported beam. I just wanted to explain or understand the basics of the problem. Sorry for the bad explanation.
The point is that I expect only positive reactions there. I modeled it using "contact" in NX and I got that, which I assume is what happens in reality. 
My question is: why do I get positive and negative values in my model? Could it be because it is not free to rotate, as you mentioned?
Thanks!

 

[ThomasH]

My question is: why do I get positive and negative values in my model? Could it be because it is not free to rotate, as you mentioned?

That would be my guess. Why not simply try locking only one node and see what happens?

 

[Alex Szatmary]

Yeah, the issue is that your simple support has 3 nodes. If you had this setup in real life, you'd get compression on the left end of that support but the right end would bend up and not be in contact. Look at what kind of contact you're modeling—it seems that separation is not occurring.