how do i can seperate body parts from each other? i tried to set some constrains to breakable but then the mesh just stretches. thanks!
Hahaha! brilliant 
Stretch Armstrong
I expect the easiest way to handle this would be to spawn a separate arm mesh and hide the arm bone of your character.
Ye ULLS, i also thought of this way but its not rly flexible. If i want every part to get cut i have to produce a seperate mesh for everything + a stump that prevents from looking into the mesh. I heared about a way to convert a skeletal mesh into a skeletal destructible mesh but cant get any informations just saw it into a showcase video on youtube. So breaking constrains doesnt work that way?
I have limited knowledge in this area and am also looking into the best way to handle it. The last I heard, destructible skeletal meshes were not supported by default. I think separate meshes is the way to go really. If you do however come up with a better solution, please PM me the details. 
i will tell you