FEA on sheet metal parts

[Rich76]

Hi Guys,

New to this forum but hopefully someone has an answer to
this one.

I've run many successful FEAs over the years with Pro-
Mechanica, but this is the first large sheet-metal
bracket I have run.
I get the model meshed and constrained correctly using
the shelled method, but every time I come to run the
static analysis it fails, highlighting a series of
elements around the sheet metal bend line.
I have tried remodelling as a basic solid (with and
without the rounds) but it still does not work.
Is there anything else I need to set-up with this part.
It is around 320mm long and 170mm high with a material
thickness of 1.5mm.
Is it because of the potential large deflections in the
run that causes it to fail??

Thanks

 

[story]

Hi, can you give here the part?

 

[ankarl]

Welcome to the forum!


At least show loads and constraintsand a partial picture to give some understanding of your problem.

I dont work with such thin material but I made a simple L-profile with your overall dims and could run it without crash soyours might have some complexity issues.
Edited by: ankarl

 

[Rich76]

Sorry, didn't realise I could add files at first. I have
attached an image showing geometry and where I have
constrained and loaded the part.

Thanks

<a target="_blank" href="uploads/Rich76/2012-08-22_080156_Capture.zip" target="_blank">2012-
08-22_080156_Capture.zip</a>

 

[ankarl]

How did you fix the blue zones?
If they are constrained I would try to release the constraint at the left side. At least in Z-direction.

 

[Rich76]

Blue zones were fixed displacement, locking movement and
rotation in X, Y and Z. I did try releasing some of the
constraints in Z but applied this to all 3 zones.

I'll try what you have recommended and let you know how I
get on.

Many thanks for your support.

 

[Rich76]

Had a go with no luck.

Tried around ten different ways of releasing/locking
constraints but keep getting the same message shown
below:

"The design study terminated abnormally.

The model is insufficiently constrained for the analysis.
Please review the element connections, properties, and
constraints. If this is a modal analysis, then you may
be able to obtain a solution by requesting additional
modes.

You may be able to locate your model's problem area by
using Mechanica database ID numbers. ID numbers can be
queried using the "Entity ID" macro in Mechanica
Standalone. The following ID numbers are associated
with this error:

373698
374122

The unconstrained degree of freedom can be seen by
running
a constrained Modal Analysis with rigid mode search.
Animating the rigid modes will display the unconstrained
degrees of freedom. If the error still occurs, then the
issue could be caused by material properties or
unattached
spring/mass idealizations."

Any thoughts?

 

[indigo2]

Check the last paragraph of the error message. It suggests that you set up and run a modal analysis. If you do that, and then review the animated results, you will get a better understanding of what the solver 'sees' as being under constrained. Make sure to set the check box for the rigid mode search when you define the modal analysis.

Also note that rotation DOF's are significant in shell elements, so you'll want to make sure the model is properly constrained. That's the sticky wicket in your case, it seems.
Hope that helps. keep us posted.

-tsl

 

[Kevin Ling]

Maybe your meshing is not correct. Try to make the meshing more dense

 

[Ray Ellender]

Run a modal, as suggested, but first check whether your material has Young's Modulus and Possons Ratio entered. If they are 0 , or not entered, it gives this kind of failure message, even if the constraints are Ok . This happens with WF3 and later because it now uses the Pro/E database (not a separate Mechanica database)and if a material has been entered by a Pro/E designer, he probably didn't give it this data


PS It is highly unlikely to be a meshing problem

 

[hasan_t_almasri]

Would you please attache the model so we can look at it?

I am faced with this many time. Using Denser meshing in
and around the failure area helps.

 

[mneal]

I have always had good luck looking at animated modal
/eigenvalue results for this type of error.

 

[Ray Ellender]

If you are constraining or loadinga surface that degenerates to an edge when you shell compress, then Mechanica won't like it. Constrain one of the edges instead.


I suggest that you contact PTC's Technical support and also post the model here