Hello Wayne,

Here is a link to the archive of my model:

When you change a Flexible part to Rigid, you can’t apply a Pressure load. Reread my description above where I explain that the force caused by the missing pressure is calculated by hand.

When you change a Flexible part to Rigid, the Contact must have the Rigid part on the Target side of the Contact definition. Right click on the contact and select the Flip item in the popup.

In the 1020 model archive, I missed that the circular part was Steel. You will need to recreate the Steel wire if you want to use my model. Use a smaller diameter to allow the nylon to have space to mesh around it.

The way I did my model, holding the Outer Cylinder fixed while the Balloon inflates is more efficient from a solution elapsed time point of view. Raising the Outer Cylinder using a Displacement Joint Load in step 2 is also more efficient for solution elapsed time. You will find it takes longer to solve if you allow the Outer Cylinder to rise while the inflation takes place, then push it back down.

Stiffness is the derivative of the Force-Displacement curve.