I think people model it as separate parts because its easier to change the pattern +the inflation/setting part is usually done on an axisymmetric model. You can use a tie to begin with and get the rest of the model going, after that you could switch to a no separation/rough contact, that way you can simulate the pressures trying to peel it off. If you know exactly how its bonded on you can model it as a cohesive contact, but you will need the properties for that.

By the way, there is a tire modelling example workflow available in the Dassault user community, you should try to find it and see how they do it.

I agree with David's answer, previously I have simulated a buttocks-thighs tissus model with outer skin layer. I have tried to compare several cases by changing the contact types. So, you can use a tie to your model and after, you can try with friction contact cases between the two layers to compare the results.

Best regards,

David Sziroczak and He Thong Bui , Thanks a lot .