Inventor General Discussion

Inventor General Discussion

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Distinguished Contributor
skumar26
Posts: 124
Registered: ‎08-01-2008
Message 1 of 9 (1,290 Views)

inventor FEA and beam column calculator

1290 Views, 8 Replies
03-18-2012 05:58 PM

Hi All,

 

I have a confusing question.

When I try to calculate bending moment stress thru "Beam and column calcultor it shows an error that is Wk and Jk is missing. Ok that is fine. If we put values for both we will get the answer. Because I have come to know thru inv discussion that many material in the CC do not have these values.

 

Now my question is when we insert a part for example from content centre (CC) and do FEA analysis on this part. It shows some values like deflection, stress etc etc. How is that possible? one side it is not doing in the beam calculatio but other side in FEA it is doing that.

 

It means we are not going to rely upon these results in the FEA. It is the same CC, same inventor, how should be trust the result in FEA.

Anyone Please advise.

 

Thanks

Sushil

Employee
henderh
Posts: 651
Registered: ‎06-07-2007
Message 2 of 9 (1,266 Views)

Re: inventor FEA and beam column calculator

03-19-2012 01:40 PM in reply to: skumar26

Hi Sushil,

 

    When you say "FEA analysis" are you by chance referring to Frame Analysis? (and not stress analysis)

 

  I believe the Beam and column calculators (in Design Accelerator) and Frame Analysis both use beam equations to find the displacements, stresses, etc.

 

 Inventor's Stress Analysis doesn't use the classic theoretical beam equations, even for content center parts.  SA uses the FEM, which takes into account only material properties such as Young's Modulus, Poisson's ratio, etc.  As such, we don't need profile section property information like torsonal section modulus or the polar moment of inertia.

 

  Structural shapes that originate from the default CC library include all necessary section properties and these can be recognized by Design Accelerator and Frame Analysis.  However, for custom structural shapes these may be considered missing, or not used in Frame Analysis.

 

  To get around the possibility of missing section properties during authoring, Frame Analysis uses Beam Properties values that are calculated from the profile sketch's region properties "on the fly".  Torsional Section modulus (Wz) is the calculated value that may be missing only for the non-circular hollow profile class of structural shapes.  I believe this equation is not redily available through the Robot Strutural Analysis tools that FA uses, or by Inventor's region properties calculator.

 

  If say Wz (beam's torsonal section modulus) is missing, this just means that Frame Analysis won't calculate the torsional stress, but other results that do not rely on this property are still valid (e.g. bending stress).  If there is no torsional load on the member, it is fine to ignore.  If a torsional stress is likely, we can manually add (or override) this property in the Beam Properties dialog by choosing the Customize checkbox.

 

  In summary, since FEA (Stress Analysis) doesn't use section properties, I think you can trust the FEA (Stress Analysis) results for beams and structural shapes since it uses the FEM and not classic beam equations that rely on section properites.  You can trust Frame Analysis results since it uses profile properties calculated "on the fly" and will not show a result it cannot calculate due to a missing property.

 

Hope this helps.

 

Best regards, -Hugh

 

[Edit" added 'material']



Hugh Henderson
Simulation QA Engineer
DLS
Distinguished Contributor
skumar26
Posts: 124
Registered: ‎08-01-2008
Message 3 of 9 (1,252 Views)

Re: inventor FEA and beam column calculator

03-19-2012 07:05 PM in reply to: skumar26

Thanks Huge,

 

I asked this question because when I do stress analysis on a channel taken from CC. all the time the result is varying. I have done " converagence etc but there comes a big difference whenever i run or re-run the stress analysis command.

 

whenevr I apply fix constrain on the holes ( two holes on each side) and apply a total load 9000N) uniform load).

and run the stress analysis. everytime i run it it comes out with different value.

 

Please find the attached copy of the part and do this on ur system. Please let em know if u r facing or not the same problem

 

thanks

Sushil kumar

 

 

*Expert Elite*
JDMather
Posts: 28,221
Registered: ‎04-20-2006
Message 4 of 9 (1,244 Views)

Re: inventor FEA and beam column calculator

03-19-2012 07:26 PM in reply to: skumar26

I do not see a simulation in the part you attached?

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Distinguished Contributor
skumar26
Posts: 124
Registered: ‎08-01-2008
Message 5 of 9 (1,240 Views)

Re: inventor FEA and beam column calculator

03-19-2012 09:06 PM in reply to: skumar26

Hello JD,

 

No Stress analysis done in this one.

 

it is just an example.

 

The same channel I was testing last week at home and facing problems.

 

I ma in the office now.

 

Thanks

Sushil

*Expert Elite*
JDMather
Posts: 28,221
Registered: ‎04-20-2006
Message 6 of 9 (1,211 Views)

Re: inventor FEA and beam column calculator

03-20-2012 07:36 AM in reply to: skumar26

What Safety Factor are you getting on these tests?

 

SF>1?

small relative displacement?

Please mark this response as "Accept as Solution" if it answers your question.
-----------------------------------------------------------------------------------------
Autodesk Inventor 2015 Certified Professional
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Certified SolidWorks Professional
Inventor Professional 2015-SP1 64-bit
http://www.autodesk.com/edcommunity
http://home.pct.edu/~jmather/content/DSG322/inventor_surface_tutorials.htm
Employee
henderh
Posts: 651
Registered: ‎06-07-2007
Message 7 of 9 (1,190 Views)

Re: inventor FEA and beam column calculator

03-20-2012 03:53 PM in reply to: skumar26

Hi Sushil,

 

  As JD mentioned, can you show the setup and results are you getting from Design Accelerator?  If the setups are not close enough, we will get different results (of course).

 

   By fixing the holes in space it doesn't take into account the compliance of the rest of the structure.  The beam will kind of stretch in addition to bending.

 

  The fixed constraints will create a stress riser around the holes, much like fixing the end of a cantilevered beam.  If you are using h-refinement / convergence the stress result won't converge...is this what you're seeing by "...every time i run it it comes out with different value."?

 

  Attached are the results I generate using R2011_SP2. 


Best regards, -Hugh



Hugh Henderson
Simulation QA Engineer
DLS
*Expert Elite*
JDMather
Posts: 28,221
Registered: ‎04-20-2006
Message 8 of 9 (1,144 Views)

Re: inventor FEA and beam column calculator

03-22-2012 06:37 AM in reply to: skumar26

Sushil,

 

Are you still here?

I thought you might want to take this discussion further - setting up a more realistic test.

I can also check with Autodesk Simulation (Algor), Creo and SolidWorks.

Please mark this response as "Accept as Solution" if it answers your question.
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Autodesk Inventor 2015 Certified Professional
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Certified SolidWorks Professional
Inventor Professional 2015-SP1 64-bit
http://www.autodesk.com/edcommunity
http://home.pct.edu/~jmather/content/DSG322/inventor_surface_tutorials.htm
Distinguished Contributor
skumar26
Posts: 124
Registered: ‎08-01-2008
Message 9 of 9 (1,096 Views)

Re: inventor FEA and beam column calculator

04-10-2012 05:02 PM in reply to: skumar26

Hi JD,

 

Sorry I cudn't get bacj to you all. I was away from the office for few days. I am trying to do some more test and will get back to you on that FEA as soon as can.

Thanks

SUSHil

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