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Hello, I am trying to simulate the straining of a polymer with a hollowed out tube section in COMSOL. However, the main issue I am having is the simulation has an effect where the outer polymer layer eventually collapses to nonexistance and then inverts back and "regrows". My main consideration for this after trying various things is the issue of the constraint boundary that is placed in junction with the displacement boundary. I have tried different methods to only restric movement in the x direction, i.e. the force of the pull while allowing free movment in the Y and Z. This would match realistically with my physical experiments of using a strain device. I assume there is an easy method to do this, but have had no luck finding a method that works or dosen't throw an out of bounds study error. Attached is the generated gif file show casing the effect. I have removed the "strainer" ends to have just the polymer to use with boundary to see if I could adjust that futher.