Learning Forum

[nadnd]

Hi

I am trying to simulate clamps and bolts but I having a bit of a problem. I am a bit new when it comes to using ANSYS.

Can you please help me? I am trying to obtain the maximum load on the clamps. I would like to find out how tight should the bolts be and also if the washers undergoing compression will get damaged over time. 

I am using the static structural Analysis. Bolt Pretension = 6000N, Pressure = 2800Pa.

Thanks.

[peteroznewman]

Please insert an image of the clamp and the bolt so we can see the geometry. Is there only one bolt?
I understand the Bolt Pretension, what is the Pressure applied to?

[nadnd]

Thankyou for your reply.
Here is an image. There are 4 bolts and 8 clamps.
I have simplified the simulation by adding a point mass to the tube on the right and added a fixed support to the tube on the left. Is this correct?
The pressure represents the force exerted by the wind on the unit. I only have Ansys Mechanical. So, I converted the windload into pressure? Is there a different way to do it?
Thanks.

[peteroznewman]

A Pressure load acts normal to the face it is applied to, which is not the same as the force of the wind, which will act along the direction the wind is blowing. You can just assign a force to the faces and use components to define the direction the wind is blowing. Newer versions of ANSYS allow a pressure to be defined in a direction, which I find odd.
Creating bolt pretension on this configuration with 3 nuts on one bolt requires special preparation.
The Bolt Pretension load type was designed to work on a bolt with just 1 nut. The shaft is required to have a single face between the head and the nut, separate from the shaft face that is in the nut. It works by splitting that face and pulling the cut faces together to generate the load.
With three nuts, you will need to split the face of the shaft in six places: on the top and bottom face of each nut. In that way you can apply two Bolt Pretension loads, one between the head and the first nut and another between the second nut and the third nut.

[nadnd]

Thank you Peter for your help. I will give it a try.

[nadnd]

Hi Peter
It is hard to mesh the parts when splitting the faces in six places.
It results in very fine meshing which my computer can not support. How big ( how deep) of a cut it should be?

[peteroznewman]

There is no cut. The depth is zero. It is a split of the face. Take one cylindrical face and make it two by using Split Face. You should not put in a Cut.

[nadnd]

After splitting the face I am getting errors. Please read below. Thanks.

[peteroznewman]

Show details of each face along the bolt and show what loads and contacts are assigned. You might not have made enough splits to keep the Pretension face separate from the Contact faces.

[nadnd]

Please see below. Thanks.

[nadnd]

I have the same errors when
Using force instead of pressure
When changing the contact to frictional
When applying the second pretension after the 3rd nut
When introducing a cut instead of a split.

[nadnd]

Can I send you a copy of the model?

[peteroznewman]

Yes, you can reply with the .wbpz Archive file attached and say what version of ANSYS you are using.

[nadnd]

Please find attached. I am using ANSYS 2020R2. Thanks.

[peteroznewman]

I opened the attached file in ANSYS 2020R2.
What value are the washers adding? All they are doing is dragging down the performance of the solution. I recommend suppressing the six washers and move the nuts to take up the gap.
You have Bolt Pretension and a Pressure Load. The normal way to simulate this is that the Bolt Pretension is applied in Step 1, then other loads are applied in Step 2. But in your model, the Pressure is ramping on in Step 1 at the same time that the Bolt Pretension is ramping on. Don't do that.
Looking through your Contact definitions, there are holes that have a Rough Contact with the Bolt. Rough means that if the contact is closed, no sliding can occur of the hole along the bolt shaft. Don't do that. Use Frictional contact so that the hole can slide along the shaft.
Work on these problems and see how the model improves.

[nadnd]

Thanks Peter for you reply.
I have made the proposed changes but I am still getting the same error.

Thanks.