Coupled Degrees Of freedom!! Could it Be used for my case - two layered metal sheet with spotwelds

[Rhyder88]

Hello all
I straight away explain my case. I need to perform eigen value analysis for a heat insulator sheet , which is a two layered metal sheet (same material-) . These two layers are combined with use of 4 spot welds at the corners. Now i made a thin shell FE model with 2 layers and made rigid element connections at spot welding points. I fully restrained the bolt points where it is going to be fixed on the system.
i observed one non-realistic thing in the mode shapes for my FE model. the mode shape is such as, one layer(ie. weakest layer) begins to deform and the deformation of this layer is interfering and crosses over the next layer. I was aware , this is because of considering contact between these layers.
I am using I-deas SDRC, it does not support Contact set for modal analysis. So i looked for other options. Now my doubt is ,whether applying coupled degrees of freedom is the right way to consider the relative contact between these layers. If no, please clarify me , for what purposes these coupled degree of freedom can be used. In particular, "Translational Pairing."
I think the description of the problem is somewhat clear. I am ready to give more explanation if u need. I am looking forward for your replies.

 

[GregLocock]

I know that for sheet metal fatigue work far more complex proprietary methods are used to model spotwelds, but for modal analysis yours doesn't seem a bad approach. You can't strictly use contact in modal analysis because MA is linear, whereas contact is non linear.

The fact that the two sheets overlap in your animations is neither here nor there, that is an artefact of your display scaling, since modal scaling is non dimensional.

Your other problem is that the modes of adjacent sheets are heavily coupled, and damped, by the trapped air layer. I don't know how to model that in FEA.

Cheers

Greg Locock


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[Rhyder88]

Thanks for your comments Greg..
I want to know , Whether using of Laminates ll be a good option for this problem??
i am thinking of creating a laminate of two layer with same material.
But i have no idea whether spot-weld could made an effect on this laminate.
Did anybody having expertise in using Laminates for this kind of simulation??Please comment.