Contact problems in a Stress Analysis, Inventor.

[nicolas.drecq]

Hi Everybody,

I have a small issue on a stress analysis on Inventor. I need to make an analysis on an assembly made of 3 parts : 2 axles and one bigger part. Each axles has a slightly smaller diameter than the hole it fits in. I want to tell inventor to put the axles in the holes and to create the tangential contact where it would naturally goes under the applied forces :

You can see in the attached picture that I used a tangential contact (before going into the stress analysis environement) and I make the contact betwee the hole and the axles where I wanted by moving the axle. My problem is that when I do the stress analysis , inventor keep the contact as the last position it was and "melt" it so that if my contact was on the back of the hole and I put a forward forces, it will pull (on the back part of the hole) and not push on the front part.... 

Is there a way to make a better contact for two cylinder of different diameter?

Thank you very much for your help.

Nicolas

[raviburla]

Hi,

Inventor Stress Analysis offers several types of contacts. The default contact type for contacts that are automatically detected are set to Bonded Type. If the user intent is different from Bonded type, the contact type needs to be updated. Please see here for a tutorial on contacts.

From what I understand - in your case - the contacts are set to bonded and hence you are not seeing the behavior that you are expecting. If you can send the model, we will be able to give more details. Separation contact could be appropriate for your case. Please note that separation contact is a non-linear contact type - meaning that non-linear iterations are performed to identify the contact status and hence the compute times could be significantly larger when compared to bonded contacts. Also, note that the deformations and strains are assumed to be small. 

Please let us know if you have more questions.

Regards,

Ravi Burla (Autodesk)

[nicolas.drecq]

Hi Ravi thank you for your answer. 

I attached a file showing and assembly with the same issue but more simple. If I pull on the center plate with the a separation condition the axles goes through the plate and doesn't modelise the contact. To set the elements at first I used some constraints contacts and hidden them to let the separation contact acts solo.

If you have an idea or solution it would be great!

Thank you

[raviburla]

Hi Nicolas,

Thank you for the dataset. I used ideas from your dataset and created a simpler dataset as attached with this message. The model I attached does not have solution (since the file size will be too large with results data), so you will need to solve the model. Here are few points to note:

1. Inventor Stress Analysis is a Linear analysis - this means that the displacements and strains are assumed to be small. So we have to ensure that the contact distances are relatively small. 

2. I have modeled a cylinder with diameter of 24.5 mm and the cylinderical hole in the plate has a diameter of 25mm. This gives a contact distance of 0.25 mm.

3. The contacts are modeled as separation type.

4. Both the ends of cylinder are fixed and the plate is pulled with a load of 200 N. Frictionless constraints are applied on the sides of the plate to ensure that the deformation is along the direction of applied force (otherwise, the plate may rotate about the contact point)

5. I have applied local mesh controls to ensure that the contact region is properly captured by the mesh.

6. Also, plot the solution with actual deformation to see the true picture. If we use scaled deformation, it would appear the the parts are penetrating.

I am attaching the image of the solution as well. Please let us know if you have further questions/concerns.

Regards,

Ravi Burla (Autodesk)

[nicolas.drecq]

Hi,

A lot of thanks for your work!! It s clearer to me know.

I tried to make the same model but I still get a strange penetration of the parts. I assume you created yours on Inventor 2015, could you send it to Inventor 2014 because I get a problem of RSE.

Thanks for all.

Nico

[raviburla]

Hi Nicolas,

I am attaching the model with inventor 2013, so it should easily open in versions >= 2013. Also, I am attaching an image with few settings: (a) Showing actual deformation (b) Updating the color bar max value so that we can see the stress gradients properly.

Please let us know if you have more questions.

Regards,

Ravi Burla (Autodesk)

[nicolas.drecq]

Works like a charm.

Thank you very much for your time and work.

Have a good week.

Nicolas