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Pin and rotation in mechanica/Simulate

gfraulini
17-Peridot

Pin and rotation in mechanica/Simulate

Hi all,

I would propose to you a simplification of a problem: putting in rotation drum that push a capsule.

I would see if the path of the capsule gives some problem.

generale.JPG

I've made a simplification of the assembly, in the hypothesis that the mid plane of the caps will remain in the axis of the path.

I've make a solid surface that simulate the surface of the path where the capsule slide.

semplificazione.JPG

Here I have two problems:

1) the capsule cross the surface despite I've put the contact regions

2) I'm not able to put in rotation the drum without a big distortion of it.

I've done a little assembly where I try only to make the "pin".
I attach also this file.

Someone could tell me the issue?

Thanks


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3 REPLIES 3

Giulio,

I have not investigated your model thoroughly, but I see a few possible causes. In the first model, "prova" there does not seem to be any forces or prescribed displacements. As far as I can see, you have put a constraint on the surface that is also a contact surface. This is not something I would have tried. In addition, there is a large initial gap in your contact. This can be problematic in a contact analysis, especially if you, as in your case, do not include large deformations.

I'm not sure how the structure is loaded/constrained in reality, so it is difficult for me to anticipate where the capsule will contact the "PM1A30019" component, and how those contact forces are transmitted to constraints.

Suggestions:

-model parts/assembly so that there is minimal initial gap in contacts.

-make sure locations for constraints and contacts are well defined, and don't mix them, i.e. put contacts and constraints on the same surface.

-Include large deformations in your analysis (necessary in statically indeterminate models with contacts) - but this does not allow weighted links. You will have to model your link differently.

-if possible, use symmetry, so as to eliminate one possible direction of motion. Provided you do not want to analyze "out of plane" motion of the capsule, then there is a symmetry plane at the centre of the PM1A30019-part.

In the first assembly I'd tried to rotate the drum in two way:
1. imposing the rotation with constrain rotation
2. applying a little pression (that's always normal to the surface, even during the rotation) on a tooth
3. applying a little momentum as load at point

I don't remember exactly which of them are resumed within the attached assemblies; now I'm at home and I've Creo only at work.

I did not constrain the same surfaces of the contacts. On upper surface of "superficie" there is the contact; on the undersurface there is the constrain.

I've tried to let the simulation starts with the caps already in contact with the surfaces and not yet.

The only directions of motion let the capsule are the xy of the mid-plane.

I think the problem might be the fact that I didn't abilitate the large deformations because I thought that, since there aren't big deformations of material, it wasn't necessary. I forgot that the "large deformation" command is necessary regardless of the material's deformation where, like here, "the nodes of model move very" in the space.

I attach the link of a video that shows an application similar to mine but where the displacement is linear.

http://learningexchange.ptc.com/tutorial/4691/performing-a-contact-analysis-in-ptc-creo-simulate-3-0-ptc-live-global-15

If you use the "large deformation" plus a load, it works.

But there is a thing that I don't understand: since you don't impose a displacement (in this case an angular one) but only a load, the displacement is function of the time that the load is applied because there isn't reaction in the other direction.

But if I increase the end time step (within the output tab) from 1 to 5, the displacement remains the same.

Moreover, I continue don't understand how can I impose an angular displacement with a pin. I've tried a pin on the inner cylindrical surface and a radial displacement on the outer one (in the "large deformation" you can't use "theta" expressed in radians, so I expressed it in millimeters as an arc (radians * radius); but it didn't work...

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