Creating FEM from assembly

[limtom77]

I took two blocks (separate parts) and created an assembly file, and placed surface constraints to fuse the two boxes together.

Then I created a FEM from the assembly, which automatically takes the assembly and makes it become one part file.

With this part file which represented two blocks fused together, I restrained one block, and I created a pulling pressure on the second block. When I ran the solution, the blocks separated - they came apart!

Why does it do that? When I created the assembly, I constrained the two parts together before creating the FEM part. Shouldnt the blocks be constrained together?

Please advise.

Thanks

 

[Liro]

You'll have to constrain the two parts together after creating the FEM.

As a guideline, you can create FEM's for both parts with restrain and load set etc. Then after creating the assy FEM combine the previously created sets and join the two parts together with beams, contact, constrains etc.

 

[limtom77]

are you saying to create two separate FEM's for the two different part files. then place both FEM's onto the workbench and create restraints between the blocks?

 

[limtom77]

hm... i tried creating two separate FEM's for each part, but the system only lets me place one FEM on the workbench at one time.

i've also tried creating an assembly, but when i try to mesh, the system automatically turn the assembly into a single part file. is there a such thing as a "FEM assembly"? wasn't sure if you were literal when you said "assy FEM".

do i create the restraints while in the "assembly" workspace, or in the "boundary conditions" workspace?

again, thanks.

 

[LeonEng]

Hi,
I don't think the constraint in CAD model can be automatically translated into FE constraint, although Ideas has good CAD-CAE interface. In your case, you need to define interface element (i.e. spring element) between the 2 blocks to represent the joint. BTW, what are you evaluating? the fused joint or the block? You may need to model the detail of the joint if you wish to evaluate the joint. on the other hand, you may not need to model 2 separate block if the joint is very rigid & the blocks are to be evaluated. You can always simplified the model with appropriate boundary conditions to represent the actual situation.

 

[Liro]

To be more specific:

You have an assembly with two blocks. Create FEM's for both parts and mesh them. Put the assy to the workbench (no FEM's). Then in meshing or boundary conditions task choose 'Create FEM from assembly'. Specify a name for a part to be created (I-DEAS creates a part with those two blocks and the created part is related to the original assy). Choose the two FEM's you've created and update the assy FEM from the window (also check the options such as 'add part geometry'). Put away the original assy from your workbench and leave the created part and the assy FEM on. Now restrain your model and solve it.

Hope this helps.

 

[limtom77]

Liro, if I use your method do I still need to add the *springs* that LeonEng mentioned?

I tried your method -- meshed two blocks, created assembly of two blocks, then CONSTRAINED the two blocks in assembly, then created FEM From Assembly, selected the two FEM's, updated, RESTRAINED the part, then ran solution, and the two blocks separated again.

Any additional advice would be appreciated.

 

[Liro]

The constraints created in modeler or assembly task won't affect the FE model (as LeonEng mentioned).

As you now have a FE model with two blocks with initial gap, use for example the springs to connect them. Also restrain the other block. For both pick only nodes to make sure that desired characteristic are achieved.

PS. You might wanna check the I-DEAS Help library for additional info.

 

[sarangb]

Did you tried to make the mesh to overlap.
there is a option which makes the nodes in two seperate parts overlap so they act as constrained.
If nodes are not common between two parts you won't be able to solve for assembly.
In FEM all the calculations are done with respect to nodes.

Hope this helps you.

Sarang