Patent Publication Number: US-10329925-B2

Title: Vibration-damped composite airfoils and manufacture methods

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     Benefit is claimed of U.S. Patent Application Ser. No. 61/846,306, filed Jul. 15, 2013, and entitled “Vibration-Damped Composite Airfoils and Manufacture Methods”, the disclosure of which is incorporated by reference herein in its entirety as if set forth at length. 
    
    
     BACKGROUND 
     The disclosure relates to damping of gas turbine engine components. More particularly, the disclosure relates to damping of fan blades of turbofan engines. 
     Gas turbine engine components are subject to vibrational loads. One particular component is fan blades of a turbofan engine. 
     US Patent Application Publication 2013/0004324 discloses use of a carbon fiber fan blade airfoil body with a metallic leading edge sheath. US Patent Application Publication 2012/0070270 discloses a vibration dampener for vane structures containing carbon nanotubes. US Patent Application Publication 2012/0321443 discloses a vibration-damping rotor casing component containing carbon nanotubes. 
     In other fields, various patent applications reference the presence of nanotubes in composites. These include US Patent Application Publications 2012/0134838, 2012/0189846, 2013/0034447, 2009/0152009, 2004/0092330, 2007/0128960, and 2013/0045369 and International Application Publication WO2010/084320. 
     SUMMARY 
     One aspect of the disclosure involves a turbine engine component comprises a fiber structure forming at least a portion of an airfoil. A matrix embeds the fiber structure. A carbon nanotube filler is in the matrix. 
     A further embodiment may additionally and/or alternatively include the carbon nanotube filler in the matrix existing through a thickness of at least three plies of the fiber structure. 
     A further embodiment may additionally and/or alternatively include the fiber structure forming at least 30% by volume of a composite portion of the component. 
     A further embodiment may additionally and/or alternatively include the fiber structure forming 45-65% by volume of a composite portion of the component. 
     A further embodiment may additionally and/or alternatively include the airfoil being an airfoil of a turbine engine blade. 
     A further embodiment may additionally and/or alternatively include the airfoil being an airfoil of a turbofan engine fan blade. 
     A further embodiment may additionally and/or alternatively include the airfoil being an airfoil of a turbine engine vane. 
     A further embodiment may additionally and/or alternatively include the airfoil being an airfoil of a turbofan engine fan vane. 
     A further embodiment may additionally and/or alternatively include the fiber structure comprising at least 50% carbon fiber by weight. 
     A further embodiment may additionally and/or alternatively include the fiber structure comprising one or more woven members. 
     A further embodiment may additionally and/or alternatively include the matrix comprising a cured resin. 
     A further embodiment may additionally and/or alternatively include the carbon nanotube filler having a content of 0.05-0.49% in the matrix by weight. 
     A further embodiment may additionally and/or alternatively include the carbon nanotube filler having a characteristic diameter of 0.5 nanometer to 5 nanometers and the carbon nanotube filler having a characteristic length of 10 nanometers to 100 nanometers. 
     A further embodiment may additionally and/or alternatively include the carbon nanotube filler in the matrix is in a multi-ply thickness of the fiber structure, inter-ply and intra-ply. 
     A further embodiment may additionally and/or alternatively include the carbon nanotube filler in the matrix being in a jacket and a core of the fiber structure. 
     A further embodiment may additionally and/or alternatively include a method for manufacturing the component The method comprises adding a mixture of the carbon nanotube filler and a precursor of the matrix to the fiber structure or a precursor thereof. 
     A further embodiment may additionally and/or alternatively include positioning the fiber structure in a mold. 
     A further embodiment may additionally and/or alternatively include the adding comprising injecting said mixture into the mold. 
     A further embodiment may additionally and/or alternatively include the adding comprising applying the mixture to pre-impregnate a sheet, a tape or a tow. 
     A further embodiment may additionally and/or alternatively include a method for using the component. The method comprises: placing the component on a gas turbine engine; and running the engine, wherein the carbon nanotube filler damps vibration of the component. 
     The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partially schematic half-sectional view of a turbofan engine. 
         FIG. 2  is a view of a fan blade of the engine of  FIG. 1 . 
         FIG. 3  is a sectional view of the blade of  FIG. 2 , taken along line  3 - 3 . 
         FIG. 3A  is an enlarged view of the blade of  FIG. 3 . 
         FIG. 3B  is a further enlarged view of a ply of the blade of  FIG. 3A . 
     
    
    
     Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
       FIG. 1  shows a gas turbine engine  20  having an engine case  22  surrounding a centerline or central longitudinal axis  500 . An exemplary gas turbine engine is a turbofan engine having a fan section  24  including a fan  26  within a fan case  28 . The exemplary engine includes an inlet  30  at an upstream end of the fan case receiving an inlet flow along an inlet flowpath  520 . The fan  26  has one or more stages  32  of fan blades. Downstream of the fan blades, the flowpath  520  splits into an inboard portion  522  being a core flowpath and passing through a core of the engine and an outboard portion  524  being a bypass flowpath exiting an outlet  34  of the fan case. 
     The core flowpath  522  proceeds downstream to an engine outlet  36  through one or more compressor sections, a combustor, and one or more turbine sections. The exemplary engine has two axial compressor sections and two axial turbine sections, although other configurations are equally applicable. From upstream to downstream there is a low pressure compressor section (LPC)  40 , a high pressure compressor section (HPC)  42 , a combustor section  44 , a high pressure turbine section (HPT)  46 , and a low pressure turbine section (LPT)  48 . Each of the LPC, HPC, HPT, and LPT comprises one or more stages of blades which may be interspersed with one or more stages of stator vanes. 
     In the exemplary engine, the blade stages of the LPC and LPT are part of a low pressure spool mounted for rotation about the axis  500 . The exemplary low pressure spool includes a shaft (low pressure shaft)  50  which couples the blade stages of the LPT to those of the LPC and allows the LPT to drive rotation of the LPC. In the exemplary engine, the shaft  50  also drives the fan. In the exemplary implementation, the fan is driven via a transmission (not shown, e.g., a fan gear drive system such as an epicyclic transmission) to allow the fan to rotate at a lower speed than the low pressure shaft. 
     The exemplary engine further includes a high pressure shaft  52  mounted for rotation about the axis  500  and coupling the blade stages of the HPT to those of the HPC to allow the HPT to drive rotation of the HPC. In the combustor  44 , fuel is introduced to compressed air from the HPC and combusted to produce a high pressure gas which, in turn, is expanded in the turbine sections to extract energy and drive rotation of the respective turbine sections and their associated compressor sections (to provide the compressed air to the combustor) and fan. 
       FIG. 2  shows a fan blade  100 . The blade has an airfoil  102  extending spanwise outward from an inboard end  104  at an attachment root  106  to a tip  108 . The airfoil has a leading edge  110 , trailing edge  112 , pressure side  114  ( FIG. 3 ) and suction side  116 . The blade, or at least a portion of the airfoil is formed of a fiber composite. Exemplary fiber is carbon fiber. Exemplary matrix is hardened resin. 
     In the exemplary blade, the fiber composite portion forms a main body  120  of the airfoil and overall blade to which a leading edge sheath  122  is secured. Exemplary leading edge sheathes are metallic such as those disclosed in US Patent Application Publication 2003/0004324A1, entitled “Nano-Structured Fan Airfoil Sheath” (hereafter the &#39;324 publication). Although the exemplary illustrated configuration is based upon that of the &#39;324 publication, other configurations of blades and other articles are possible. Other airfoil articles include other cold section components of the engine including fan inlet guide vanes, fan exit guide vanes, compressor blades, and compressor vanes or other cold section vanes or struts. 
       FIG. 3  is a sectional view of the blade of  FIG. 2 .  FIG. 3A  is an enlarged view of the blade of  FIG. 3 . The exemplary fiber composite portion comprises a core  123  and a jacket or envelope  124 . The exemplary core  123  is formed of multiple plies  125  of fiber (e.g., carbon fiber). Exemplary core plies are or include woven plies. The exemplary jacket  124  comprises plies  126  of fiber differing in composition or form or arrangement from those of the core. This may also be a carbon fiber. The exemplary jacket  124  comprises five plies of carbon uni-directional (UD) tape, as a specific instance of a particular ply architecture and layup i.e. [0/90/0/90]. Other layups e.g. [0/+45/−45/90] or [0/+60/−60/90] may also be used. Other ply architectures e.g. 2D and 3D weaves can also be used in place of UD tape. Other structures may have three or more or four or more ply thickness (e.g., both core and jacket). 
       FIG. 3A  shows (not to scale in order to illustrate structure) the matrix material as  128 . Actual inter-ply thickness of the matrix would be much smaller than shown. 
     The exemplary carbon fiber forms at least 30% of the composite portion body  120  or blade  100 , more particularly, 45-60% or at least 45-70% by volume (fiber volume fraction). Exemplary composite is at least 30% of the overall article (e.g., allowing metallic features such as the sheath), more particularly, at least 50% or at least 60% by weight. 
     As is discussed further below, the matrix material  128  contains a carbon nanotube (CNT) filler  130 . The filler serves to increase vibrational damping. Again, this is not to scale as the carbon nanotubes would be invisible if at the scale of ply thickness shown.  FIG. 3B  is a partial sectional view of an individual ply  125  or  126  showing matrix and CNT filler infiltrated into the plies and surrounding individual fibers  140  of the ply. Again, this is not to scale relative to the  FIG. 3A  callout. 
     Exemplary CNT concentration in the composite is at about 0.1-4.0% by weight, more particularly, 0.1-2.0% by weight, more particularly, 0.1-1.5% by weight. Exemplary characteristic (e.g., mean, median, or mode) CNT diameter is 1 nanometer, more broadly, 0.5 nanometers to 2 nanometers or 0.5 nanometers to 5 nanometers. Exemplary characteristic (e.g., mean, median, or mode) CNT length is 20 nanometers, more broadly, 10 nanometers to 50 nanometers or 10 nanometers to 100 nanometers. 
     In an exemplary sequence of manufacture, sheets of woven carbon fiber are placed in a mold in a lay-up process. The core may have been separately formed or may be formed as part of a single lay-up process. Uncured matrix material containing the CNTs is then injected into the mold (e.g., in a resin transfer molding (RTM) or vacuum assisted resin transfer molding (VARTM) process). 
     In an exemplary sequence of manufacture, the CNTs are mixed along with the mixing of resin and hardener (and catalyst or other additive, if any). Exemplary CNT concentration in the uncured matrix prior to injection is at least 0.05% by weight, more particularly, 0.05-0.49%, more particularly, 0.12-0.24%. 
     In alternative manufacture sequence, the carbon fiber sheet may be a prepreg., preimpregnated with the resin and CNTs. Similar prepreg. tapes or tows may be used in fiber-placed processes. 
     The use of “first”, “second”, and the like in the following claims is for differentiation within the claim only and does not necessarily indicate relative or absolute importance or temporal order. Similarly, the identification in a claim of one element as “first” (or the like) does not preclude such “first” element from identifying an element that is referred to as “second” (or the like) in another claim or in the description. 
     Where a measure is given in English units followed by a parenthetical containing SI or other units, the parenthetical&#39;s units are a conversion and should not imply a degree of precision not found in the English units. 
     One or more embodiments have been described. Nevertheless, it will be understood that various modifications may be made. For example, when applied to an existing baseline configuration, details of such baseline may influence details of particular implementations. Accordingly, other embodiments are within the scope of the following claims.