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Analytical results very different to inventor stress analysis results.

17 REPLIES 17
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Message 1 of 18
christaylor92
1072 Views, 17 Replies

Analytical results very different to inventor stress analysis results.

Hi, 

I'm trying to model a hollow, rectangular cross-section beam. It is 0.6m high, and 0.45m wide. The walls are 0.01 thick, meaing the dimensions of the inner rectangle are 0.58m and 0.43m. The beam is 6m long, of the material "Steel, mild", fixed at each end, and with a force of 9800N applied on the top face.

The results Autodesk Inventor give me are very different to my analytical results.

My analytical results state the max stress should be 15.9MPa, and the max displacement 0.5mm.

However, Autodesk gives the max stress as 2.8 MPa, and the max displacement as 0.07mm.

Is there something I'm doing wrong?

 

I have tried using hollow beams with thicker walls, in case the thin walls were a problem, but I am still getting very different results.

17 REPLIES 17
Message 2 of 18
GSE_Dan_A
in reply to: christaylor92

Post part here and perhaps others can try performing the FEA on it to verify results.


Regards,

GSE Consultants Inc.
Windsor, ON. Canada
Message 3 of 18
JDMather
in reply to: christaylor92


@christaylor92 wrote:

...fixed at each end,.


Make sure the constraint application matches the real world and matches the hand calc.

I have found that often the and calc set-up doesn't match the real world constraints if care isn't taken.

 

Attach your file here and describe it's true attachments at ends and true area of load (across entire beam or in a specific area).


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Message 4 of 18
christaylor92
in reply to: GSE_Dan_A

Part attached

Message 5 of 18
christaylor92
in reply to: JDMather

Thanks for your reply, I have attached the part in the post below yours.

The part is fixed over the cross-sectional area at each end, and the load applied over the area of the top face.

Message 6 of 18
JDMather
in reply to: christaylor92

I do not see a simulation set up in that file?

No fixed constraints, no load?


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Message 7 of 18
blair
in reply to: JDMather

I ran it through Sim-Mech 2014

 

Max Dis: 0.0377mm

Maxvon Mises: 1.735 N/mm^2

 

This is with both end surfaced fully fixed. Are you sure you don't mean "simply supported"?


Inventor 2020, In-Cad, Simulation Mechanical

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Message 8 of 18
christaylor92
in reply to: JDMather

Here's the file with the simulation

Message 9 of 18
christaylor92
in reply to: blair

I'm pretty sure it was fixed, but is there a way to simply support within autodesk?

Message 10 of 18
blair
in reply to: christaylor92

You need to use the Vectors tab to control the directions of constraint


Inventor 2020, In-Cad, Simulation Mechanical

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Message 11 of 18
blair
in reply to: christaylor92

Use the pack-and-go for this as you have omitted all the FEA fiels


Inventor 2020, In-Cad, Simulation Mechanical

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Message 12 of 18
JDMather
in reply to: blair


@Blair wrote:

Use the pack-and-go for this as you have omitted all the FEA fiels


All the information is defined in the latest file - re-running the simulation recreates the missing data files.


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Message 13 of 18
JDMather
in reply to: christaylor92


@christaylor92 wrote:

My analytical results state the max stress should be 15.9MPa, and the max displacement 0.5mm.

However, Autodesk gives the max stress as 2.8 MPa, and the max displacement as 0.07mm.


My guess is that the formula you used allows rotation at the ends (around the X-axis in this case) and probably translation towards the center (in this case Z translation), while in Inventor you have fully constrained the end faces.  This results in tight ends (they remain vertical and fixed in place, no rotation or translation towards the center), and therefore less displacement.

 

Hand  Calc.png

 

 

Also this is a thin part (in relation to overall size).  Using the Midsurface analysis might be better, but I haven't used that yet.


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Message 14 of 18
blair
in reply to: JDMather

Thanks, used to Sim-Mech with the related files stored in a separate directory.

 

You are getting a "Thin-Wall" warning with this model. Results will be different than hand calculations

 

I would look at the PDF results I posted running Sim-Mech as more accurate.


Inventor 2020, In-Cad, Simulation Mechanical

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Message 15 of 18
christaylor92
in reply to: blair

Surely with simply supported the maximum stress would be even lower?

Message 16 of 18
christaylor92
in reply to: JDMather

Thanks, this could be the problem. But, I also conducted the analytical calculations with a solid beam, and it gave me very similar answers to Inventor.

Is there a way to adjust the constraints within inventor?

Message 17 of 18
christaylor92
in reply to: blair

Ok, thanks. Where abouts is this vectors tab?

Message 18 of 18
blair
in reply to: blair

Expand the Contraints Box, double >> in lower RH corner.


Inventor 2020, In-Cad, Simulation Mechanical

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