You have to apply a local contact set between the 'shell' and 'solid' parts. The local contact set is the grey contact, under connections.
Thanks for your answer but i have already put those contact as you can see in the picture, in french (contact entre composants).
And for your information it's not a shell but a tube with a thickness of 0,5mm but i don't think it's a problem.
You have used a 'global' contact set (green). I can't tell if the components have initial contact, but if not you must use a 'local' contact set (grey).
By the way, you have used a 'no penetration' contact. So the parts are not connected, and can separate from eachother. I guess you need a 'bonded' contact.
Try an online tutorial about connections.