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rmerlob
Posts: 128
Registered: ‎10-21-2011
Message 1 of 30 (856 Views)
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FEA interpretation

856 Views, 29 Replies
10-08-2012 01:49 PM

Hi,

 

Ever since I started using inventor a couple years ago I´ve done hundreds of simulations on different parts test models etc, I feel that I´ve asked every question that needs to be asked and read every white paper/article/tutorial on FEA that I could possibly find.

 

The problem is: I still cant be confident when I interpret the results I get, I totally understand FEA requires training and experience to use and its not a tool that should be used blindly, but I cant seem to rely on even the simplest of results.

 

So this time my aproach will be different, I´m not going to direct my question to a single area or post results:

 

Will the part attached hold 70 kN under traction using Ductile Iron 65-45-12?

 

I´m sure a lot things regarding stress concentration, localized plastic strain, constrain placement are going to come up but  I really dont want to steer the topic in any direction, just want to see what other people come up with and discuss.

 

Thanks for your attention,

 

RM

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JDMather
Posts: 26,306
Registered: ‎04-20-2006
Message 2 of 30 (818 Views)

Re: FEA interpretation

10-09-2012 08:47 AM in reply to: rmerlob

How will the part be manufactured? Machined from a casting?

 

It appears that there would be interactions with another part(s) that would apply the load and limit the displacement currently exhibited in the analysis.

 

More questions to follow....

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karthur1
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Message 3 of 30 (802 Views)

Re: FEA interpretation

10-09-2012 02:12 PM in reply to: rmerlob

Here is my stab at it. You said the load was in "traction".  Not sure what you mean by that, but I assumed you meant in tension.  I set it up with the id of the end opposite the eyes being fixed. For the load, I did a bearing load of 70kN on the id of the eyes. The load direction is away from the the end that is bored out.

 

Inventor gives me a minimum SF of .91.  According to this analysis, it would probably start failing in the hole where the pin will be.  This is assuming that there is nothing between the two tangs that prevent them from "closing in".

 

Load Case 1.jpg

 

If there is some element that keeps the tangs straight, then this will fail sooner.  It gives me a minimum SF=.46 under this load case.

 

Load Case 2.jpg

 

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JDMather
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Message 4 of 30 (797 Views)

Re: FEA interpretation

10-09-2012 02:41 PM in reply to: karthur1

More information is needed.

An entry into the plastic deformation zone of the curve does not necessarily indicate "failure".  It does not necessarily mean fracture of the part.

 

The key is to match up a digital analysis model to physical testing of actual part, then you can have predictive confidence in (very) similar digital models.

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rmerlob
Posts: 128
Registered: ‎10-21-2011
Message 5 of 30 (777 Views)

Re: FEA interpretation

10-09-2012 10:25 PM in reply to: rmerlob

Hi, thanks for answers

 

Yes I did mean tension, language barrier :smileytongue:

 

JD, the part that comes with this one goes in the middle and has about double the section, it leaves about 4 mm total clearance inside, so i dont think it will stop movement towards the inside. I'll post it when I get to work tomorrow.

 

We are going to cast with the two small holes and bore/drill the other one out, they are used for holding cables.

 

Interesting thing is, we are pretty certain this is the material that these are made of, did a spectrometric analysis for composition and even though carbon is imposible to read on cast ductile iron, all other elements suggest it is, plus they have a 70 kN stamp on them, they are also made by casting and drilling like I described.

 

I understand that due to strain hardening of the local high stress the part should not be asumed to fail even if a small part of it passes yield, is that right?

 

Did I miss some other critical info?

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karthur1
Posts: 4,165
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Message 6 of 30 (739 Views)

Re: FEA interpretation

10-10-2012 06:29 AM in reply to: JDMather

JDMather wrote:

More information is needed.

An entry into the plastic deformation zone of the curve does not necessarily indicate "failure".  It does not necessarily mean fracture of the part.

 

The key is to match up a digital analysis model to physical testing of actual part, then you can have predictive confidence in (very) similar digital models.


Testing the actual part is the best way to determine when it will fail.  Hard to argue that.:smileyhappy:
Any SF < 0.69 in this case, would indicate that its out of the plastic range and past the ultimate tensile. Its up to the OP to determine his criteria for "failure" (either facture or deformation). I would think that with a clevis, it could be deformed, but not broken, and be considered a failure.
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JDMather
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Message 7 of 30 (733 Views)

Re: FEA interpretation

10-10-2012 06:55 AM in reply to: karthur1

karthur1 wrote:
 I would think that with a clevis, it could be deformed, but not broken, and be considered a failure.


Deformed by how much? 0.5% 1% 10?  any permanent deformation a failure?

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karthur1
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Message 8 of 30 (725 Views)

Re: FEA interpretation

10-10-2012 07:16 AM in reply to: JDMather

Thats totally up to the OP and how the "failure" is defined.

 

If the clevis is used for rigging, then normally ANY noticable deformation would deem the part unuasble. But, if it is used for something else, then it might might be reused as long as it was not "broken".

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JDMather
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Message 9 of 30 (721 Views)

Re: FEA interpretation

10-10-2012 07:23 AM in reply to: karthur1

karthur1 wrote:

...ANY noticable deformation would deem the part unuasble.


Is that by eyeball inspection, measuring instrument, or digital analysis?

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rmerlob
Posts: 128
Registered: ‎10-21-2011
Message 10 of 30 (708 Views)

Re: FEA interpretation

10-10-2012 09:51 AM in reply to: JDMather

karthur:

 

''Any SF < 0.69 in this case, would indicate that its out of the plastic range and past the ultimate tensile. Its up to the OP to determine his criteria for "failure" (either facture or deformation). I would think that with a clevis, it could be deformed, but not broken, and be considered a failure.''

 

Actually, I believe that since Inventor uses linear analisys whe cannont assure its actually past UTS because of strain hardening, for example attached you can find my best attempt at using Autodesk Simulation with a bi-lineal material model, and you can see SF is a lot higher. 

 

Material is 80-55-06 Ductile but you can see the diference from the results I get on Inventor.

 

Like you, I believe any permantent deformation should be avoided, thats not what im seeing and it puzzles me that I have a real part in my hands that has the 70 kN stamp on it.

 

Of course I'm not a finite elements expert so i would really like someone with more experience and training to comment. 

 

Also attached is the other part too.

 

thanks for replies

 

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