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problem with buckling / snap through (FR : flambement / cloquage)

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Newbie

problem with buckling / snap through (FR : flambement / cloquage)

Hi !

I have a plate, clamped between two walls; the plate is curved on the left and I impose a déplacement to the right side, so the plate will come to an unstable position and then will move to the right side;

I use large displacements analysis, and I include the 'snap through 'option

I have a fatal error :

" conception anormalement interrompue. Affaissement structurel détecté lors du calcul du cloquage"

which means 'structural softening/ weakening (or buckling?) detected during snap through...

but there is no hint on how to solve...

(see picture below)

Does someone has an idea ?

by the way, when a force is imposed instead of a displacement, there is no fatal error but the snap through phenomenum is not detected ..

thank you

marc

same in french :

bonjour ,

j'ai une plaque encastrée des deux cotés, légèrement incurvée (5mm ) à gauche; j'impose un déplacement de 25 mm vers la droite; logiquement, on devrait passer par une psoition instable, puis la structure devrait passer en position stable à droite (c'est une structure bistable), correspondant au phénomement dit de cloquage dans creo;

il se trouve que ce cloquage pose probleme (erreur fatale)...

comment résoudre ce probleme et traduire ce phénomemene d'instabilité ?

merci

7 REPLIES 7
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Re: problem with buckling / snap through (FR : flambement / cloquage)

Hello, Jojo_lyn,

Could you tell us what is the version of Creo and attach your picture.

Possibly the file.

Merci pour votre texte en français.

Kind regards.

Denis.

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Re: problem with buckling / snap through (FR : flambement / cloquage)

Hi Denis,

Thank you for your help; I use CREO 2. So, here is the situation :

I have a plate, clamped between two walls (top and bottom); the plate is curved on the left and I impose a déplacement to the right side, so the plate will come to an unstable position and then will move to the right side; I use large displacements analysis, and without the 'snap through 'option, I got an acceptable result in terms of displacements, but not in terms of force because the force is always increasing;

without_snap_through_cloquage.png

in fact, the force shoud decrease after an instable point,and this can be detected using the 'include snap-through' option ('inclure le cloquage' - see ptc help:

http://help.ptc.com/creo_hc/creo30_sim_hc/usascii/index.html#page/sim/simulate/analysis/struct/refer...

);

THE PROBLEM is that, when using this option, the snap through is detected (as it should be), but the program returns a fatal error... I tried to increase the number of steps in the analysis, but it doesn't help; when a force is imposed instead of a displacement, there is no fatal error but the snap through phenomenum is not detected ..

include_snap_through_cloquage_erreur.PNG

thank you for your help !

marc

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Re: problem with buckling / snap through (FR : flambement / cloquage)

Marc,

I can run a similar example without problem. I do not use the "snap through"-option. If I use this I too get an error message. I use a prescribed displacement, and create a measure for the reaction force. I have also used symmetry, and mapped mesh to get fewer elements.

It is not meaningful to apply an increasing load, since as you say, the direction of the force will reverse as you pass through the unstable position. Creo Simulate can't capture this; it would require an explicit solver that can capture the acceleration and the mass force as the clip snaps over to the other side. This happens very fast, so I'm not sure how one would apply a steadily increasing force. Using a prescribed displacement makes more sense, this way you analyze what happens if you slowly force the clip from one stable side to the other. The reaction force becomes negative (changes direction) as you pass the unstable position, see graph below, measure "Force" vs "Time", i.e. displacement.

Capture.PNG

/Mats Lindqvist/Suède

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Re: problem with buckling / snap through (FR : flambement / cloquage)

Good points, Mats.

"I can run a similar example without problem. I do not use the "snap through"-option. If I use this I too get an error message. "

I've noticed that there appears to be something wrong with solver for Creo. There's a benchmark snap-through model that solves perfectly fine in WF5, but fails to solve in Creo. The model has several loads and constraints to minmic the same event by using either an enforced dispalcement or an applied load (i.e. the enforced displacement is always numerically stable, while the applied load isn't). The model has three studies:

WF5

Model 1: Constraints and Enforced Displacement - Solves without issue.

Model 2: Constraints and Applied Load w/ Snap-Through - Solves without issue.

Model 3: Constraints and Applied Load w/o Snap-Through - Failes to solve.

This model shows the functionality of the snap-through feature rather nicely. However, if you try to solve this model in Creo:

Creo 2.0 M100

Model 1: Solves without issue.

Model 2: Fails to solve.

Model 3: Solves, but doesn't obtain the correct reaction load.

Creo 3.0 F000

Model 1: Solves without issue.

Model 2: Fails to solve.

Model 3: Solves, but doesn't obtain the correct reaction load.

I submitted a bug report to PTC about this quite a while ago, but I never heard back from them. It's somewhat concerning that there could (potentially) be such a large bug within the solver.

Re: problem with buckling / snap through (FR : flambement / cloquage)

Shaun,

can you provide me with the SPR number. I'd like to have a look at the status.

Gunter

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Re: problem with buckling / snap through (FR : flambement / cloquage)

Gunter,

It looks like never received a SPR number (there were some issues with the SCN at the time, but it had never prevented a submission before). I've gone ahead and re-submitted it with the benchmark model I used (case:12224387).

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Re: problem with buckling / snap through (FR : flambement / cloquage)

Thank you!

I see, SPR 2245065 has already been filed for it later yesterday - public article CS188059 is available for reference: http://support.ptc.com/appserver/cs/view/solution.jsp?n=CS188059

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