Patent Publication Number: US-2018038386-A1

Title: Fan blade with composite cover

Description:
BACKGROUND 
     This disclosure relates to gas turbine engines, and more particularly to fan blades for gas turbine engines. 
     A typical gas turbine engine includes a fan section including a fan rotor. The fan rotor includes a fan hub, with a plurality of fan blades secured to the fan hub and extending radially outwardly from the fan hub. In some gas turbine engine fans, the fan blades are hollow, or have cavities extending through the fan blades to reduce weight of the fan blades and/or improve operational performance of the fan blades, when compared to a solid fan blade, having no cavities. The hollow fan blades are typically formed from a metal material, such as titanium, and are typically fabricated by diffusion bonding a relatively thin cover onto a blade body with hollow cavities. This manufacturing process requires extensive investment in capital equipment and often produces dimensionally non-conforming parts. Alternative processes have been explored, one of which consists of adhesively bonding the cover onto the blade body. Lighter weight cover materials, such as carbon/epoxy composite, have been considered as well. Manufacturing trials for this configuration indicated that the elevated cure temperature of the epoxy film adhesive (approximately 250° F.), combined with the coefficient of thermal expansion mismatch between the titanium body and the composite cover, results in a distorted blade shape at room temperature. This distortion would be more pronounced at lower temperatures where the difference between the stress-free temperature (200 F-250° F.) and the coldest expected operating temperature (−65 F) is even greater. 
     SUMMARY 
     In one embodiment, a fan blade assembly for a gas turbine engine includes a blade body, a blade cover secured to the blade body and an adhesive layer to secure the blade cover to the blade body, the adhesive layer configured to set at ambient temperature. 
     Additionally or alternatively, in this or other embodiments the adhesive layer includes a urethane, silicone, epoxy or polysulfide material. 
     Additionally or alternatively, in this or other embodiments the blade cover and the blade body define one or more blade channels in the fan blade assembly. 
     Additionally or alternatively, in this or other embodiments the blade body includes one or more ribs. 
     Additionally or alternatively, in this or other embodiments the one or more blade channels extend in a substantially radial direction. 
     Additionally or alternatively, in this or other embodiments the fan blade assembly is configured for an operating temperature between −65 and 200 degrees Fahrenheit. 
     Additionally or alternatively, in this or other embodiments the blade body is formed from a first material and the blade cover is formed from a second material different from the first material. 
     Additionally or alternatively, in this or other embodiments the blade body is formed from a metal material and the blade cover is formed from a carbon fiber reinforced composite material. 
     In another embodiment, a method of forming a fan blade assembly for a gas turbine engine includes forming a blade body, forming a blade cover separate from the blade body, and adhering the blade cover to the blade body via an adhesive layer located between the blade body and the blade cover, the adhesive layer configured to set at ambient temperature. 
     Additionally or alternatively, in this or other embodiments the adhesive layer includes a urethane, silicone, epoxy or polysulfide material. 
     Additionally or alternatively, in this or other embodiments one or more blade channels are defined between the blade cover and the blade body. 
     Additionally or alternatively, in this or other embodiments one or more ribs are formed in the blade body. 
     Additionally or alternatively, in this or other embodiments the one or more blade channels extend in a substantially radial direction. 
     Additionally or alternatively, in this or other embodiments the fan blade assembly is configured for an operating temperature between −65 and 350 degrees Fahrenheit. 
     Additionally or alternatively, in this or other embodiments the blade body is formed from a first material and the blade cover is formed from a second material different from the first material. 
     Additionally or alternatively, in this or other embodiments the blade body is formed from a metal material and the blade cover is formed from a carbon fiber reinforced composite material. 
     In yet another embodiment, a fan assembly for a gas turbine engine includes a fan hub and a plurality of fan blades extending radially outwardly from the fan hub. At least one fan blade of the plurality of fan blades includes a blade body, a blade cover secured to the blade body, and an adhesive layer to secure the blade cover to the blade body. The adhesive layer is configured to set at ambient temperature. 
     Additionally or alternatively, in this or other embodiments the adhesive layer includes a urethane, silicone, epoxy or polysulfide material. 
     Additionally or alternatively, in this or other embodiments the blade body is formed from a first material and the blade cover is formed from a second material different from the first material. 
     Additionally or alternatively, in this or other embodiments the blade body is formed from a metal material and the blade cover is formed from a carbon fiber composite material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter which is regarded as the present disclosure is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the present disclosure are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a schematic illustration of an embodiment of a gas turbine engine; 
         FIG. 2  is a schematic illustration of an embodiment of a fan section of a gas turbine engine; 
         FIG. 3  is a cross-sectional view of an embodiment of a fan rotor of a gas turbine engine; 
         FIG. 4  is a cross-sectional view of an embodiment of a fan blade for a gas turbine engine; and 
         FIG. 5  is a plan view of an embodiment of a fan blade for a gas turbine engine. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a schematic illustration of a gas turbine engine  10 . The gas turbine engine generally has a fan  12  through which ambient air is propelled in the direction of arrow  14 , a compressor  16  for pressurizing the air received from the fan  12  and a combustor  18  wherein the compressed air is mixed with fuel and ignited for generating combustion gases. 
     The gas turbine engine  10  further comprises a turbine section  20  for extracting energy from the combustion gases. Fuel is injected into the combustor  18  of the gas turbine engine  10  for mixing with the compressed air from the compressor  16  and ignition of the resultant mixture. The fan  12 , compressor  16 , combustor  18 , and turbine  20  are typically all concentric about a common central longitudinal axis X of the gas turbine engine  10 . 
     The gas turbine engine  10  may further comprise a low pressure compressor  22  located upstream of a high pressure compressor  24  and a high pressure turbine located upstream of a low pressure turbine. For example, the compressor  16  may be a multi-stage compressor  16  that has a low-pressure compressor  22  and a high-pressure compressor  24  and the turbine  20  may be a multistage turbine  20  that has a high-pressure turbine and a low-pressure turbine. In one embodiment, the low-pressure compressor  22  is connected to the low-pressure turbine and the high pressure compressor  24  is connected to the high-pressure turbine. 
     Referring now to  FIG. 2 , the fan  12  includes a fan rotor  30  having a fan hub  32  located at the central axis X and a plurality of fan blades  34  extending radially outwardly from the fan hub  32 . In some embodiments, the fan blades  34  are secured to the fan hub  32  by, for example, welding, while in other embodiments, such as shown in  FIG. 3 , the fan hub  32  includes a plurality of hub slots  36  into which a blade root  38  is inserted and secured at the hub slot  36  by a retainer (not shown). Referring again to  FIG. 2 , each fan blade  34  extends radially outwardly from the fan hub  32  from the blade root  38  to a blade tip  40 , and extends along the central axis X from a blade leading edge  42  to a blade trailing edge  44 . 
       FIG. 4  illustrates a cross-sectional view of fan blade  34  taken along a selected radius between the blade root  38  and the blade tip  40 . The fan blade  34  is a hollow fan blade  34 , having one or more cavities  46  located inside the fan blade  34 . The fan blade  34  is constructed from a blade body  48  having a first external side  50  and a first internal side  52 , with the first internal side  52  having a plurality of ribs  54  or other features formed therein. A blade cover  56  is secured to the blade body  48  at the first internal side  52 , with the blade cover  56 , the blade body  48  and the ribs  54  defining the cavities  46 . Referring to  FIG. 5 , in some embodiments the ribs  54  extend in a substantially radial direction between the blade root  38  and the blade tip  40 . It is to be appreciated, however, that in other embodiments the ribs  54  may extend in other directions. 
     Referring again to  FIG. 4 , in some embodiments, the blade body  48  is formed from a metal material, such as a titanium material, while the blade cover  56  is formed from a composite material such as a carbon fiber and epoxy composite material with the blade cover  56  secured to the blade body  48  by an adhesive material layer  58 . The thermosetting polymer adhesive material layer  58  is of a material that initially cross-links and sets, or hardens, at room temperature to secure the blade cover  56  to the blade body  48 . The materials utilized may include: urethane, epoxy, silicone, and polysulfide compounds. Utilizing such an adhesive does not require an initial elevated temperature cure cycle to set the adhesive and secure the blade cover  56  to the blade body  48 , thus reducing the residual thermal stress and distortion in the fan blade  34  from coefficient of expansion differences between the titanium blade body  48  and the composite blade cover  56  at its typical operating temperature, which ranges from −65 F to 200 F. 
     While an elevated temperature cure cycle, at above room temperature, for example, 250 degrees F., is not necessary, in some embodiments such a cure may be performed to improve mechanical properties of the adhesive. Although some distortion may occur during the elevated temperature cure cycle, the since the stress-free condition of the fan blade  34  is at room temperature rather than at the elevated temperature, the magnitude of the distortion will be reduced. 
     While the present disclosure has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the present disclosure is not limited to such disclosed embodiments. Rather, the present disclosure can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the present disclosure. Additionally, while various embodiments of the present disclosure have been described, it is to be understood that aspects of the present disclosure may include only some of the described embodiments. Accordingly, the present disclosure is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.