US Patent 10422348 Unsymmetrical turbofan abradable grind for reduced rub loads

A containment structure comprising an annular structure configured to provide close tolerance to a rotation structure. The containment structure includes a first abradable structure, a second abradable structure, and a shroud that is defined in part by the first abradable structure and in part by the second abradable structure. An annular surface of the shroud is defined by the first abradable structure and by the second abradable structure. The first abradable structure is harder than the second abradable structure.