## General Mechanical

#### How to simulate decompression?

• Puhan
Subscriber

I have two bodies, one encloses another.

I the first they both are stressed by the same amount but after that they are decompressed that means pressure reduced on both of them. I want to simulate this but can't figure out how. Can anyone please answer I will be grateful. I have the model and everything just need help idea to simulate decompression.

Regards

Bhanu

• peteroznewman
Subscriber
Please insert an image of the cross-section showing the two materials.
Are the materials bonded to each other or is there a sliding interface?
• Puhan
Subscriber

Thank you very much for the quick comment.

Below is the model, they are bonded to each other.

Actually, I am doing an analysis on a rock which brought to the surface from the ground. The only pressure is changing from high pressure to zero pressure. That is my main query how can the decompression be modelled like let's say the first scenario both systems are in 6GPa of pressure and then they are decompressed to 0GPa. Kindly please let me know.

Regards
Bhanu

• peteroznewman
Subscriber
Looking at your mesh, I see a large block meshed with large elements and a small object meshed with small elements, but it doesn't look like the large block has a small object cavity in it. If the large block has no cavity where the small object is, that is wrong. Open the geometry in SpaceClaim and use the Combine tool to subtract the small object from the large block, but keep the small object. Then go to the Workbench tab and click the Share button. By doing that, you won't need any Bonded Contact. The mesh will connect the small object with the face of the cavity in the large block.
In Mechanical, use a Kinematic Mount to connect three corners of the large block to ground. See this discussion on how to do that. https://forum.ansys.com/discussion/comment/137006#Comment_137006
Apply a 6 GPa pressure on all six faces.
Create a multi-step analysis.
In Step 1, 6 GPa is applied.
In Step 2, use the INISTATE command to zero the stress in the model. Use the Search button to find information about this command.
In Step 3, change the pressure to 0 GPa. This represents the decompressed state of the rock.
• Puhan
Subscriber

Thank you very very much.

I understood the mesh connectivity thing, thank you very much.

But still, I can't understand the decompression analysis.

I want to understand the physics of two bodies (small and bigger). Actually, the inner body has a lower modulus of elasticity than the outer side. I just want decompression happening from 6 GPa (that means both systems are confined to 6 GPa) initially. In the second step, however, the decompression should start which means the outer body would be expanding more slowly than the inner body (because of a higher modulus of elasticity than the inner). This will in turn give rise to stress to the boundary and I want to study that stress.

However, I couldn't understand your recommendation properly, my apology for that.

From step 1 to step 2, there will be simulation in both systems that mean they both will be compressed which I don't need, I just need the decompression immediately starting from 6 Gpa to 0 GPa in that step.
I couldn't properly understand the difference between step 2 and step 3, kindly please let me know.

Regards
Bhanu

• peteroznewman
Subscriber
Maybe what I suggested above is not what you want. In what state do the two materials have zero stress?
Here is a thermal example. Let's say you heat up a flat sheet of glass to a high temperature, then a silver metal coating is plasma deposited on the surface to make a mirror. Let's assume that the coating of sliver has zero stress as it solidifies, and the glass also has zero stress at that high temperature.
Now let the silver coated glass sheet cool down. As the temperature is reduced, stress develops at the interface between the glass and the silver due to the difference in the thermal expansion coefficient. ANSYS can model this by setting the environmental temperature to that high value, then apply a thermal condition of room temperature. The materials will develop a coating stress during the simulation in one step. The solver knows how to apply temperature, so this thermal model is easy to do.
Not pushing on something is hard to simulate. There is something called Inverse Solving that may be what you want. That is where you take a model such as your block with 6 GPa on it, and request a solution that shows the shape of the part when 0 GPa is applied.
Read the ANSYS Help, Mechanical APDL, Structural Analysis Guide, Chapter 8.7 on Inverse Solving.
That starts with the deformed shape with a known load and solves for what the shape of the part is with no load.

Open ANSYS Help and copy the URL below, then paste that into the address of the browser running ANSYS Help.
https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v221/en/ans_str/strnonlininversesol.html
• Puhan
Subscriber
Dear
Thank you very much. This seems very interesting, however, I tried to solve the problem by equivalent modelling a static one in terms of residual stress in the inclusion and end stress in the host.

Thank you very much again.

Regards
Bhanu