Inertia welded shaft and method therefor

#The present invention relates generally to gas turbine engines, and, more specifically, to rotors or drive shafts therein.

#An aircraft gas turbine engine typically includes one or more drive shafts for transferring torque from one rotating component to another. For example, in a turbofan engine, the fan is driven by the low pressure turbine (LPT) by a first drive shaft, and the compressor is driven by the high pressure turbine (HPT) by a second drive shaft disposed concentrically around the first drive shaft.

#The drive shafts must be formed of suitable high temperature, high strength materials for carrying loads during operation at elevated temperatures. Both shafts are subject to torsion loads as the turbines drive the corresponding fan and compressor. The pressure forces acting across the fan, compressor, and turbines place the corresponding drive shafts under tension during operation. The drive shafts are also subject to bending and gravity loads as the engine elastically deflects during aircraft movement.

#The subject matter that is regarded as the invention is particularly pointed out and distinctly claimed in the concluding part of the specification. The invention, however, may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which:

#FIG. 1 shows a half cross-sectional view of a finished shaft constructed in accordance with the present invention.

#FIG. 2 shows an exploded view of the individual components of the shaft of FIG. 1.

#Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views, FIG. 1 illustrates an exemplary shaft 10 which is an integral assembly of several generally annular components disposed coaxially about a centerline A, including sequentially from front to rear: a forward shaft 20, a first transition piece 30, a composite mid shaft 40, a second transition piece 50, and an aft shaft 60.

#The forward shaft 20 and the aft shaft 60 are monolithic components constructed from a metal alloy capable of being heat treated to achieve high strength. Examples of suitable alloys include high-strength nickel-based alloys such as INCO alloy 718 or THERMO-SPAN alloy. The forward and aft shafts have suitable features for attaching them to other components in the engine. For example, the forward shaft 20 may be attached to the fan rotor (not shown) and the aft shaft 60 may be joined to the low pressure turbine (not shown) by splined or bolted joints.

#The mid shaft 40 is constructed from a metal matrix composite (MMC). In the illustrated example the mid shaft 40 comprises a titanium matrix with reinforcing fibers embedded therein. Suitable metal matrix composites are commercially available. For example, the reinforcing fibers may be silicon coated carbon, silicon carbide, or tungsten fibers integrally formed in the titanium matrix. This MMC and others are commercially available from Textron, Inc., Lowell, Mass.; Atlantic Research Co., Wilmington, Mass.; and 3M Company, Minneapolis, Minn. They have a modulus of elasticity of about 29-32×106 psi, for example, which is about double that of a conventional monolithic titanium drive shaft. The drive shaft may therefore be made thinner and lighter for comparable strength.