Thanks
My thought as well. However, reliance on the structure itself to abrade shortens the life of the blade. A coating on the inner cowl needs replacement periodically, and the performance degrades over time (albeit in predictable, though expensive fashion).
I would add "accretable" tip structures to the blades made of metallic infused ceramic. The resultant crystalline oxides would add dimension to the fan diameter over time conceivably with no limit life. As friction due sealing creates oxides, the material serves as a "growing" gasket.
patent pending.