StaticMeshes have both Simple collision (the Physics Bodies that you create in your 3D art package or in the StaticMesh Editor) and Complex collision (per poly collision) which can be composed of a number of different materials each with their own differing Physical Materials. To set the Complex Collision Physical Material see: Assign a Physical Material to a Material.
To set the Simple Collision Physical Material for a StaticMesh:
Double Click a Static Mesh in the Content Browser to bring up the Static Mesh Editor.
Change the Simple Collision Physical Material property in the Static Mesh Settings category to the desired Physical Material.
Click Save .