Differences in results between practice, theory and SW Simulation

Simulation
1

Hello

I have a first question that no one has been able to answer me: What is the purpose of the strain curve? How should it be interpreted? (As much as the curves of stresses and displacements vary according to the loads, the curve of the deformations remains almost zero and similar whatever the load)

The second and more important issue concerns the problem of difference in the results presented in the attached PDF file that I cannot explain.

The only way in this "very small assembly of 3 parts" to obtain a result close to theory and practice (1.8mm) is to declare  contacts in "No penetration". All the results in "Solid" contact give displacements of about 0.45mm (This is still 3 times less than theory or practice..)

In addition, we cannot declare "No penetration" contacts on a larger assembly because this causes balance defects, solver defects, displacements of 60 meters... (Unless you put connectors everywhere which ultimately comes down to the "Solidary" option)

I redid the simulations keeping only the profile with the load (To eliminate the "problems" of assembly and contact) But the results are the same (Approx. 0.45mm) in static, dynamic, with fixed movements or in plane support.

I hope I made a mistake somewhere or that you can help me. Because if the results are 3 times less on a simple profile, what will be the result and the veracity of the results in a large assembly?

Thank you in advance for your help


simulation_avec_resultats_faux.pdf
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Edit   : Deleted because the requester finds me arrogant in my answers

 

 

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Hello Zozo_mp

To be on the safe side, I took care to specify "I hope I made a mistake somewhere"

I admit that my RDM courses have been a few years. My goal is simply to find answers and solutions.

For information, before putting my post I consulted several BE who work on SW and PTC but unfortunately no one was able to explain these results to me by testing and redoing the calculations on their side.

I didn't choose the beam option because the purpose of the exercise was precisely to check the veracity of the results on something simple before applying tests to an assembly and a 5mm larger sheet. The versions of SW differ depending on the design offices surveyed but in general it's pro or premium.

I have already attached the simple profile.

Thank you in any case for your help

 

 


export_profile_seul.zip
4

Hello

 

The biggest misunderstanding comes from the so-called 'solidarity' contacts.

A joint contact is a welding/gluing: the nodes are completely welded between the different elements and they move in the same way.

So you have the desired result in §4.1 (in practice it's the only one that really represents what you did)

Your calculation shows a stress of 635 Mpa -> plastic deformation on your S235 JR steel: so SW will not be able to give the true value

Your calculation does not take into account gravity: the sheet metal is made of steel, which is not negligible compared to your point load.

 

In conclusion, RDM and finite element analysis is a real job. It takes a certain amount of knowledge and experience not to make mistakes.

The hardest part, as you can see, is to manage to put the right loads and the right conditions at the limits.

 

Don't forget that SW is:

-provided with tutorials

-help tools (it helps to understand the differences between 'solidarity' and 'no penetration' for example)

Reading the help, tutorials, SW examples and  the various posts of this forum related to simulation will also help you to progress

 

What really worries me is: "I consulted several design offices who work on SW and PTC but unfortunately no one was able to explain these results to me by testing and redoing the calculations on their side."

If they do FE calculations using SW simulation, consider changing subcontractors...

 

Good luck

 

 

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To avoid having coins that go to infinity:

-put a small friction coeff at the level of the contacts (like 0.05): generally it works well even if sometimes it moves a little

- model a half assembly (with symmetry)

 

Small comment: managing to simulate and calculate the part alone without putting the 2 supports and the management of the contact is great art under Simulation: you have to block an edge (without blocking the rotations) on one side and constrain the opposite edge in a reference plane (still without blocking the rotations)

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Hello

You have the 2020 version so I don't read your file or your simulation conditions.

I asked you which version you have for the simulation (which module because there are two or three)

Can you post an image (an attachment) of your simulation settings.

I am posting my comments to you upon receipt of the information I am missing.

Kind regards

1 Like
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Edit   : Deleted because the requester finds me arrogant in my answers

8

Sorry, I think I offended you with the term "False", I should have put "different from practical reality" to be more accurate. 

Far be it from me to criticize SW, PTC or others which are great tools.

To answer the fact that "Your calculation does not take into account the seriousness". I had put it on and then removed it because it hardly changed the results (I think the part is too small but I put it back in the attached simulations)

To answer the question "two tubes located at both ends and at 90° are fixed" as described in the document on the practical test, I assembled everything with clamps on a work surface (we can therefore consider that the parts form a whole as if they were welded). Caliper under the profile to measure the displacement in the center before and after the load is placed. Try it at home, it's quick and easy to do. You will see that in any case the displacement exceeds 0.4mm in reality.

Attached are the simulations of the profile alone with the parameters and gravity in addition.

Finally, yes it's scary when even BEs can't represent the deformation of a simple profile with such a powerful tool. That's why I'm asking the questions on this forum and I'm asking you the question the other way around.

What for? What are we doing wrong? (Wrong type of analysis, wrong parameters,..)

Are you able to provide a simulation of the profile subjected to this load at the center, representative of the practice as an example so that everyone can learn and improve?

Thank you for your help.

 

 

 


statique_et_non_lineaire.pdf
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Edit   : Deleted because the requester finds me arrogant in my answers

 

 

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 @Zozo_mp:  

  VERY VERY   ANGRY MODE ;-(

@+

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Hello @gt22 

Excuse me! But I reason on rigor rather than a more approximate mode.

I didn't mean to annoy you, but sometimes there are things that ..........
I can delete my post if you want

Kind regards

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  @Zozo_mp

No, no, don't delete anything .

I just notice that you're a little annoyed 

and I completely understand from reading some posts

have a good weekend @ you

@+ ;-)

1 Like
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Hello Zozo_mp,

No, you shouldn't delete the post. That's interesting...

On my simulations I didn't change anything because of the gravity applied in addition to the previous exchanges. I just took screenshots to see the settings applied as you asked me to.

Are there any errors in the parameters indicated in the simulation?

Do you think that the result obtained from a displacement of 0.4mm corresponds to the reality of a part in a metallurgy workshop? (The 0.4mm is correct and the 1.7mm of my editing does not reflect reality for the reasons you explained )

Are the assembly (1.57mm) and the result obtained (0.4mm) both wrong (Bad study, wrong parameters, on our part..). If so, could you simply provide us with a pack and go as requested of a simulation of the profile with its load representing the actual displacement that the profile should have? (It's two minutes of work with your skills on SW and as they say a picture is often worth much more than a long speech.)

Thank you

14

Hi all

Modest contribution, to be consulted in the attached pdf file, which may explain some of the discrepancies between theory, measurement and simulation.

Happy reading...


poutre.pdf
2 Likes
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Hello m.blt,

It's not a "modest contribution" that you made, it's you who are too modest compared to a certain Zozo_mp to whom I will respond in the next post.

You provide a clear, simple and well-argued answer in a single answer. I just say congratulations and thank you for all the readers of this forum.

I thought SW had a reason to give these results since I had the same results on other software (see attachment) but I couldn't explain the difference between physical measurement and simulation.

I think the explanation comes, as you said, that the difference is 4x between the two cases (And therefore huge for such small displacement measurements, 4x0.45 = 1.8, we find the two values subject to discussion).

For my part, my assembly was  more like a "solid" type assembly (the clamps having a hell of a clamping force) than a "no penetration" type

It is as you say the fact that "Even with summary means, the 1.5 mm value of the deflection seems very important..." that led me to look for a rational explanation that you have given us. I will try to improve my editing to observe the differences and try to bring practice closer to simulation.

I will also put a document from the Ecole Polytechnique in my next post that will demonstrate to some people that it does not necessarily take means worthy of NASA to do experiments with suspenders!

Once again, a BIG THANK YOU to you m.blt


appuis_simples_et_encastres.pdf
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To respond to the arrogance of Zozo_mp

When people go to a forum it's in the hope of finding help and explanations. Not because I'm the best and I criticize everyone. 

You should take an example from m.blt which is your opposite but in a good way. 

Your answers like "several BEs for a very simple thing. If the incriminated BEs did not offer a trip to the Parthenon to the plaintiff, it is because they were totally unemployed." A design office that uses SW does not necessarily do simulations all day long with it, there are really specialized design offices for that. Anyway, I'm going to keep my friends and my subcontractors who are probably more competent than you in the field in general.

At least they did some calculations and tried to understand, unlike you who didn't answer any questions about the accuracy of the parameters that were entered in the simulations and who were unable to provide any example of simulation as an example for the forum members. Not even a simple profile... ironic for someone who comes out of great theories at all costs and who thinks he's the best...

You should come down to earth a bit...

What you say: "Have a total knowledge of the characteristics of the tube to 1/10th of a mm.
1bis) be 100% sure of the quality of the steel of all components with certificates"

When my loyal supplier for years gives me a profile telling me that it is S235, I trust him. Do you know many companies that can afford to check all the parts at 1/10 before carrying out an assembly?? (Apart from a few companies specializing in precision assembly)

What you say:1°) it must be fixed on a marble (no one does metrology on a workbench with clamps attached).
2°) before fixing, measure with a comparator and not a, (even if it is electronic and claiming dimensions to the hundredth)  the incidence of  warping on the future measurement point in the center of the 30 x 5.
 

For your information, I put a doc from  the Polytechnic School of Sousse which shows that you don't need supernatural means to do tests and that it works even with a comparator... Between us, the difference with a marker between 0.4mm and 1.8mm can even be seen by eye (If not , on this one I know the answer... maybe you should consider an ophthalmologist) 

Thank you for following your statements "I believe that I have answered in full and even beyond your concerns which is why I will not continue this discussion" This will unfortunately lower your answer score but will prevent me and probably others from wasting time with great theories and no concrete answer at the exit.. (You must have fiber, not materials but policy :-))

Cdt

 

 


fascicule-tp-rc3a9sistance-des-matc3a9riaux.pdf