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Fatigue with contact from MES ?

13 REPLIES 13
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Message 1 of 14
benalain
766 Views, 13 Replies

Fatigue with contact from MES ?

Hi,

 

 

The fatigue module is designed to also handle computations from MES results.

Is it also the case when the MES momdel has contact ?

 

 

Thanks

13 REPLIES 13
Message 2 of 14
bjorn_fallqvist
in reply to: benalain

Hi, Benelain

 

I would think this largely depends on the problem, and if it is applicable also to a large extent on the contact settings. From what I know of fatigue, it is largely empirical methods to quantify a safety against failure, based on e.g. stresses and strains (as in fatigue wizard). So the short answer I guess is that; if the contact is properly set up to accurately compute the stresses and strains, then yes the fatigue wizard should handle it.

 

Just remember that the entire fatigue area and the stress/strain-based models that the fatigue wizard itself is based on are subject to limitations and some uncertainties, too.

Message 3 of 14

Hi Alain,

 

Fatigue analysis (generally speaking) is done on a set of results (load case) that can come from a static of MES analysis.

 

As Bjorn stated above, this is an empirical method of taking into account for a given loads, its variation over time and predict life.

 

I would assume that all depends on THE load case that you consider. If your physical condition consist of a cyclic fatigue due to contact, it should be sufficient to do an MES and then identify the situation (load case) where the assembly is undergoing its most critical stress distribution and use that for your fatigue analysis.

 

Regards,

Shakeel

Message 4 of 14

a little typing mistake:

 

"Fatigue analysis (generally speaking) is done on a set of results (load case) that can come from a static or MES analysis."

Message 5 of 14
benalain
in reply to: shakeel.mirza

Hi Shakeel

 

 

The assembly should have 2 sollicitations, compression and torsion.

The goal of the fatigue analysis is to know if during 1 year (with a given number of cycles), the assembly should be ok or not

 

 

ALAIN

Message 6 of 14
S.LI
in reply to: benalain

I agree with all replies here.

I don't see why contact in MES will give troubles in FW.

 

The only thing you should be careful with is that contact might result high "stress concentration" along the contact surface, which perhaps makes FW obtaining a inaccurate estimate.

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Message 7 of 14
alphaprise
in reply to: benalain

Hi all

 

Please correct me if I am wrong, but isn't fatigue only for LSS? I.e. cyclic loading but leadng to fatigue in the elastic range?

Message 8 of 14

It's valid for MES also, as long as the analysis itself doesn't involve any nonlinear material behaviour, I think.

Message 9 of 14
S.LI
in reply to: bjorn_fallqvist

Fatigue analysis works for nonlinear material behavior, though Fatigue Wizard doesn't calculate the nonlinear thing itself.

FW reads the FEA stress/strain result files, which include all nonlinear material responses (such as plastic strain).

 

 

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Message 10 of 14
bjorn_fallqvist
in reply to: S.LI

Yes, but Fatigue Wizard calculates the local stress/strain effects with Neuber's rule. So to add non-linear material behaviour to an algorithm that is already designed to calculate local stress/strain results would give wrong results, right?

 

I was told this by an Algor developer some time back.

Message 11 of 14
S.LI
in reply to: bjorn_fallqvist

Neuber's rule is for cases that local stress/strain concentration is not taken care nicely.

It's just a way to approach nonlinear effect with linear data.

 

I think if you have nonlinear result data, you can use it by setting "concentrated factor" as 1 that is the default in FW.

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Message 12 of 14
bjorn_fallqvist
in reply to: S.LI

Yes, but there's no way of turning off the Neuber correction. And if you instead use stress-based fatigue analysis, isn't that an assumption of linear-elastic behaviour in itself?

Message 13 of 14
S.LI
in reply to: bjorn_fallqvist

I think you are right, bjorn.

I don't know how to turn off the correction either.

 

I prefer the nonlinear result data if we could turn the correction off some day later.

 

Thanks.

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Message 14 of 14
bjorn_fallqvist
in reply to: S.LI

Yes, I think that might be a more accurate way to do it. The drawback would be that it would require a very fine mesh in all areas of stress concentrations I guess, but if only analyzing smaller components for fatigue, it might be a good idea to have the option to do so.

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