constraints for stress analysis

[Anonymous]

Hey guys,

Apologies in advance if similar questions have already been asked. I'm very new to Inventor and to 3D modelling for that matter.

I've modelled a steel workbench (please the attached) using the frame generator. The bench top (3mm steel plate) was drawn as a part and inserted into the assembly. I have the following questions:

1. When using the frame 'joining' options such as miter, trim to frame etc... does Inventor treat the frames that have been joined as welded sections (cannot move in relation to each other) or do I need to physically add the welds?
2. When applying a 'mate constraint' (I mated the bench top to the bench frame) and giving it a certain offset limit, does Inventor treat the mate as welded/bolted or do I need to apply the welds/bolts?
3. The bench will simply sit on top of a concrete slab/floor so which constraints do I need to use for the stress analysis? I tried to use 'frictionless constraint' at the base of the bench as to prevent the downward movement of the base when a force is applied to the bench top but Inventor is telling me there are not enough constraints! The stress simulation ran OK when I changed 'frictionless' to 'fixed' constraint. Why do I need a fixed constraint when a slight displacement of the frame legs is to be expected under extreme overloading? (please see the attached).

Thanks in advance for any inputs.

Pete

[admaiora · Accepted solution]

Hi Pete,

if you want to analyze a frame structure and you have already used the frame generator i suggest you to performe a Frame Analysis (beam analysis), not a Stress Analysis. No mesh, no finite elements,,,only beams..so quicker and more precise.

These two different analysis modules have differents rules and settings

(1-2) In the Frame Analysis when you use an end treatment (miter,etc) the software will add a rigid link to simulate the connexion.

Here for just an idea

https://knowledge.autodesk.com/support/inventor-products/learn-explore/caas/CloudHelp/cloudhelp/2014...

If you will perform a Stress Analysis the parts that are near inside the tolerance range will be automatic considered Bonded (welded).

Outside this range you will have to manually help the software to manage these contacts.

Anyway in the Frame Analysis you can set too  a tolerance for the rigid link automatic creation.

Here a little bit more info about it

http://help.autodesk.com/view/INVNTOR/2016/ENU/?guid=GUID-8DEA302A-D456-4D74-B5E4-1245384ADE08

3- If you will perform a Stress Analysis the error that you see is due to the not stable constraint situation.

I mean, that your assembly is still able to slide on a plane > not stable situation.

In these cases you have to choices:

-add more constraints to fix it the space

- teach to the software that you system is already ok, just remove that instability.

Just right click your simulation in the browser and edit it choosing Detect and Eliminate rigid body modes

In the Frame Analysis you have to use the constraint. Floating will be ok in your case (or custom)

You will find more info about these constraints here:

http://help.autodesk.com/view/INVNTOR/2016/ENU/?guid=GUID-374C9F02-4C37-4221-B1E3-377FF3F082BF

Good luck!

[Anonymous]

Thanks Admaiora. I really appreciate your inputs.

Pete