Metallic foam material

Abstract

Tip rub in gas turbine engines is a well-known phenomenon, and may lead to increased tip clearances, with consequent detrimental effects on the engine's performance and blade flutter margins. Heavy or repeated rubbing may cause blade tip over temperature leading to cracking and fatigue failure. The invention provides a tip for a gas turbine engine rotor blade, which under contact with the casing surface interacts with the casing surface so as to reduce the contact force and thereby reduce the energy transferred to the blade. The tip may be designed to ablate under contact with the casing surface, or to cut or abrade the casing surface, or to crush or compress of deflect under contact with the casing surface. In a preferred embodiment, the tip comprises fibre-reinforced metallic foam material.

1 . A fibre-reinforced blade tip for a gas turbine engine rotor blade, the tip designed to contact in use a casing surface of the gas turbine engine, characterised in that under contact with the casing surface the tip interacts with the casing surface so as to reduce the contact force and thereby reduce the energy transferred to the blade. 
     
     
         2 . A blade tip as claimed in  claim 1 , in which the tip is designed to ablate under contact with the casing surface. 
     
     
         3 . A blade tip as claimed in  claim 1 , in which the tip is designed to cut or abrade the casing surface under contact. 
     
     
         4 . A blade tip as claimed in  claim 1 , in which the tip is designed to crush or compress or deflect under contact with the casing surface. 
     
     
         5 . A blade tip as claimed in  claim 1 , in which the tip comprises fibre-reinforced metallic foam material. 
     
     
         6 . A blade tip as claimed in  claim 5 , in which at least some of the reinforcing fibres of the tip extend into the rotor blade. 
     
     
         7 . A blade tip as claimed in  claim 5 , in which the rotor blade comprises fibre-reinforced material and in use the reinforcing fibres of the tip are interleaved with the reinforcing fibres of the blade. 
     
     
         8 . A blade tip as claimed in  claim 1 , and further comprising a damping medium. 
     
     
         9 . A gas turbine engine rotor blade comprising a blade tip as claimed in  claim 1 .