Abaqus - Conditional boundary condition / load

[jl39]

Hello,
I have been using Abaqus for a few months now and I encountered a new problem.

First of all, let me explain my model.
I am modeling a contact pair in an axis-symmetry setting.
There is a cylindrical pressure vessel with spherical ends (slave) and there is a long rigid surface (master) in an angle to the axial direction of the pressure vessel.
The pressure vessel is inflated with an internal pressure so that the pressure vessel would be in contact with the rigid surface (at multiple points) after the deformation.
There is also an external pressure applied to the pressure vessel because it is under a fluid.

In CAE, the external pressure is defined onto the entire outer surface of the pressure vessel in the initial configuration.
So the external pressure is always there even a part of the pressure vessel starts to make contact with the rigid surface.
In reality, the external pressure would only exist where the pressure vessel is not in contact with the rigid surface and exposed to the fluid.

Is there a way to let Abaqus know to turn off the external pressure for elements or nodes that are in contact with the rigid wall?
In other words, is there a way to let Abaqus know the contact status of each element in the slave surface during the simulation and modify the load setting for those elements in contact?
If this is possible, is it also possible to change the material properties of the elements that are making contact with the rigid surface during the simulation?

Thank you.

 

[FEA way]

Such things are possible in Abaqus with the help of so called solution-dependent state variables and subroutines. You can use UAMP subroutine to define solution-dependent amplitude for pressure load.

 

[Mustaine3]

I'm not sure if it really applies to your situation, but...

There is a special option called "Pressure Penetration". It is used in combination with a contact pair. Starting from an point in the pressure area, Abaqus can apply the pressure at every element surface that has a contact pressure below a certain threshold. This is updated during the analysis when the contact regions are opening more and so expose more elements to the pressure load.

Look into the documentation for more details.

 

[jl39]

I have tried "pressure penetration" and it seemed to be working but one of my colleagues was concerned because it adds an additional unknown field output (PPRESS) to the model.
Instead of adding a new field output, I just want to have a simple pressure load on a surface and study the stress and strain of the model.

With user subroutine, I want to implement something like:
if contact_status on a node == 0
pressure_load = SOMENUMBER
if contact_status on a node == 1
pressure_load = 0

I don't think there is a predefined user-subroutine that does the above exactly.
Is it possible to code a whole new subroutine on my own?
If it is, what variable can I use to detect the contact status of the slave surface? Can LOPENCLOSE be used?

Thank you.