Patent Description:
Fan blade airfoils are composed of hundreds of prepreg, unidirectional prepreg tows, that fill the blade volume. In order to improve structural performance design iteration and optimization are conducted with ply layups for hundred plies. Ply layup comprises two primary sets of parameters: ply orientation and ply stack sequence. Ply orientation defines fiber angle for each individual unidirectional ply. Optimization processes of ply orientation evaluates and manages stress or strain at each ply and all critical locations, with the goal of driving maximum use of material (primarily fiber strength). The ply stacking sequence defines the relationship of one ply to its neighbors. The goal of staggering plies with different boundaries, results in dispersing and interleaving long and short plies. This is done in such a way as to breakup naturally occurring crack initiating sites in resin rich regions and to mitigate crack propagation by creating a more complex crack growth paths that could attenuate failure.

<FIG> is an exemplary depiction of an airfoil <NUM> where none-shuffled ply stacking is used in the ply layup with a volume filling scheme. None-shuffled implies that the plies are not shuffled. The airfoil <NUM> has a leading edge <NUM> and a trailing edge <NUM> and the plies <NUM>, <NUM>, <NUM> are systematically distributed between the outer surface (suction surface) or the lower surface (pressure surface) of the airfoil and the central region of the airfoil. From the <FIG> it may be seen that the largest plies <NUM> (chordwise) are located on the outer surfaces (the upper and lower camber) of the airfoil, while the smallest plies <NUM> (chordwise) are located at the interior, with the mid-sized plies <NUM> (chordwise) being distributed between the outermost plies and the innermost plies. The chord is a curve that that extends from the leading edge to the trailing edge and is at the mean of the pressure and suction side of the airfoil. The term "chordwise" implies a path along or parallel to the chord.

This design has several drawbacks notably that concentration of short, small area, plies and long plies provides interlaminar crack paths that can propagate from the leading edge to the trailing edge or from the outer radius (tip) of the blade to the inner radius of the blade. The segregation of long plies to one portion of the airfoil and short plies to another part of the airfoil prevents the development of crack arresting mechanisms that can improve damage tolerance and mitigate crack initiation and growth. There is therefore a need to develop airfoils where plies can be dispersed to increase crack mitigating mechanisms to improve damage tolerance.

<CIT> discloses a reinforced composite blade and a method of making a blade.

<CIT> discloses a blade, an associated manufacturing system and a manufacturing method.

<CIT> discloses a foreign-object-damage-resistant composite blade and manufacture.

<CIT> discloses a preform CMC article, a CMC article, and a method for forming a CMC article.

<CIT> discloses a composite airfoil with a locally reinforced tip region.

<CIT> discloses methods and features for CMC component repairs.

According to an aspect of the present invention, there is a fan blade airfoil in accordance with claim <NUM>.

Optionally, the wide plies and narrow plies are staggered chordwise with spanwise staggered long and short plies, or vice versa.

Optionally, shuffling comprises splitting plies of different sizes and interspersing them in the fan blade such that there is no progressive dimensional sequencing of ply size in any one particular direction from a given ply in the fan blade.

Optionally, the interleaving is conducted so as to render delamination pathways more tortuous when compared with fan blades where there is no interleaving, thus reducing the speed at which delamination progresses.

Optionally, the angle of intersection between the respective longitudinal axes is <NUM> to <NUM> degrees.

Optionally, the interleaved plies comprise fibers that comprise silicon carbide, oxide ceramics, carbon, or a combination thereof.

Optionally, the interleaved plies comprise matrices that comprise SiC, Al<NUM>O<NUM>, BN, B<NUM>C, Si<NUM>N<NUM>, MoSi<NUM>, SiO<NUM>, SiOC, SiNC SiONC, or a combination thereof.

According to another aspect of the present invention, there is a method of manufacturing a fan blade airfoil in accordance with claim <NUM>.

Optionally, bonding the interleaved plies comprises increasing the pressure and temperature on the plies.

Optionally, the shuffling is prescribed by a computer.

Disclosed herein is a tailorable shuffling scheme for manufacturing a laminated composite fan blade by Automated Fiber Placement (AFP). The method expands design space and manufacturing flexibility towards a goal of improving fan blade overall impact and mechanical performance. The method comprises shuffling plies chordwise and/or spanwise through the thickness (from pressure to suction sides) and the span (from outer diameter to inner radius) of the composite fan blade to distribute wide plies within narrow plies and short plies within long plies. The term shuffling includes splitting plies of different sizes and interspersing them in the fan blade such that there is no particular long range progressive dimensional (length, width and/or thickness) sequencing of ply size in any one particular direction from a given ply in the fan blade.

Progressive dimensional sequencing implies that there is a gradual change in any particular dimension (length, width and/or thickness) in a particular direction. For example, there may be at least three neighboring plies of gradually varying size (increasing or decreasing) before there is an abrupt change in the dimensional direction. For example, the first ply may be the widest, the second ply adjacent the first ply may be a little narrower than the first ply, and the third ply adjacent the second ply may be narrower than the second ply. However, the fourth ply will be wider than at least the third ply. The fifth ply will be either wider than the fourth ply or narrower than the second ply.

In another embodiment, wide and narrow plies are re-staggered chordwise with the aforementioned spanwise long and short plies, or vice versa. The ability to shuffle long and short plies and re-stagger wide and narrow plies within the fan blade provides the designer with an ability to control the spatial dispersion of resin rich regions within the volume of an airfoil. It can facilitate avoidance of the creation of planes with accumulated undesirable features and improve overall interlaminar capabilities. The ply dimensions and location can be adjusted to balance material tensile strength at the outer surface and shear strength at mid-plane. In addition, delamination can be initiated and confined to certain local ply interfaces.

More specifically, the method comprises shuffling short plies with long plies in the spanwise direction, wide plies within narrow plies in the chordwise direction and thick plies with thin plies in the thickness direction to avoid segregating plies of one particular dimension from plies of another particular dimension. The segregation of plies often provides a clean delamination path leading from one surface of the wing to another surface (e.g., suction side to pressure side or to trailing edge, to leading edge). By forming an interleaved layup along any imaginary straight plane or line from the suction side to the pressure side (or spanwise from the outer diameter to inner radius or chordwise from leading edge to trailing edge) of the composite fan blade, the pathway (of a crack) to a clean delamination is made tortuous thus preventing the crack from easily propagating and potentially leading to greater damage. In an embodiment, the interleaving is conducted so as to render delamination pathways more tortuous when compared with fan blades where there is no interleaving, thus reducing the extent to which delamination (of plies) may progress.

Layered structures define a wide variety of construction arrangements, including lightweight laminated composite articles. Laminated composites typically are defined by a continuous, essentially planar array of continuous fibers embedded in a matrix defining a lamina or ply, a plurality of plies forming a laminate composite. These composite articles can be arranged to meet various in-plane stiffness or strength needs by appropriate stacking of similar orthotropic plies of dissimilar orientation. Ceramic matrix composites generally comprise fibers that comprise silicon carbide, oxide ceramics, carbon, or a combination thereof. Exemplary matrix materials include SiC, Al<NUM>O<NUM>, BN, B<NUM>C, Si<NUM>N<NUM>, MoSi<NUM>, SiO<NUM>, SiOC, SiNC SiONC, or a combination thereof. An exemplary combination of fiber and matrix (in a CMC) is silicon carbide fibers and a silicon carbide matrix.

<FIG>, <FIG> are depictions of an exemplary composite fan blade <NUM> that details terms such as thicknesswise, chordwise and spanwise. These figures also attempt to show a basic example of the interleaving of plies. <FIG> provides a rough isometric view illustrating a layup that includes long and short plies (when viewed spanwise) interleaved with wide and narrow plies (when viewed chordwise). <FIG> is a chordwise view of interleaving, while <FIG> is a spanwise view of the interleaving.

The fan blade <NUM> comprises a leading edge <NUM> and a trailing edge <NUM>. The suction surface <NUM> is opposed to the pressure surface <NUM>. Left wingtip <NUM> opposes right wingtip <NUM>. As noted above, the chord is an imaginary curve that extends from the leading edge to the trailing edge. The term "chordwise" implies a path along or parallel to the chord and is the direction in which ply width (W) is measured. The span is measured from outer diameter <NUM> to the inner diameter <NUM> in a radial direction. The term "spanwise" implies a path along or parallel to the span and is the direction along with length (L) of the ply is measured. The thickness is measured from the suction surface <NUM> to pressure surface <NUM> and the term "thicknesswise" implies a path from the upper surface to the lower surface along which thickness (T) is measured. Each of the thickness (T), width (W) and length (L) is measured perpendicular to the other two dimensions. For example, thickness (T) is measured from suction surface to the pressure surface in a direction that is perpendicular to the chord and the span.

With reference now again to the <FIG>, the fan blade <NUM> comprises a first ply <NUM> having a first width W<NUM> and length L<NUM> is disposed atop a second ply <NUM> having a second width W<NUM> and length L<NUM>, such that W<NUM> is less than W<NUM> and L<NUM> is greater than L<NUM>. A third ply <NUM> having width W<NUM> and length L<NUM> is disposed adjacent the first ply <NUM> and atop the second ply <NUM> such that W<NUM> is smaller than W<NUM> and W<NUM>, but L<NUM> is greater than L<NUM> an L<NUM>. This thickness of the plies are also different from one another. The first ply has a thickness T<NUM> that is greater than the thickness T<NUM> but less than the thickness T<NUM>. By interleaving plies of different lengths, widths and thicknesses in a volume filling manner such that that the geometry and the dimensions of the fan blade <NUM> are not changed, a crack will have to propagate in a tortuous manner through the volume of the fan blade in order to bring about component failure. This increases resistance to failure and extends part life.

<FIG> depict a chordwise and spanwise views respectively of interleaved plies to enable a clearer definition of interleaving. <FIG> shows plies <NUM>, <NUM> and <NUM> that have widths that are greater than their lengths. Ply <NUM> has a width W<NUM>, ply <NUM> has a width W<NUM> and ply <NUM> has a width W<NUM> with W<NUM>>W<NUM>>W<NUM>. The plies <NUM>, <NUM> and <NUM> share longitudinal axis AA'. The length of each of these plies is L<NUM> and is measured spanwise, while the widths W<NUM>, W<NUM> and W<NUM> are measured chordwise. From the <FIG>, it may be seen that plies <NUM> and <NUM> have lengths L<NUM> and L<NUM> respectively measured in the spanwise direction that are greater than their widths W<NUM> and W<NUM> respectively measured in the chordwise direction. Plies <NUM> and <NUM> have longitudinal axes BB' and CC' respectively that are inclined at an angle θ with respect to the longitudinal axis AA' of the plies <NUM>, <NUM> and <NUM>. The angle θ is then angle between the longitudinal axes of plies that extend in the chordwise direction with the longitudinal axes of plies that extend in the spanwise direction. The angle θ may vary between <NUM> degrees and <NUM> degrees, preferably <NUM> degrees to <NUM> degrees.

From <FIG> it may be seen that the longitudinal axes of the plies that extend chordwise intersect with the longitudinal axes of plies that extend spanwise. Interleaving is therefore defined as an actual intersection of a plurality of plies of different variable dimensions that extend in the chordwise direction with another plurality of plies of different variable dimensions that extend in the spanwise direction such that their respective longitudinal axes intersect with one another at angles of <NUM> to <NUM> degrees, preferably <NUM> to <NUM> degrees.

A tortuous path is one that weaves back and forth because it is obstructed by plies that have been deliberately put in its path to prevent it from traveling uniformly in one direction. In an embodiment, the tortuous path makes at least one change in direction of at least <NUM> degrees, preferably at least <NUM> degrees, and more preferably at least <NUM> degrees.

In other words, the shuffling of plies by interspersing short plies with long plies provides the composite fan blade with a "rest" or "braking" mechanism where delamination (in the form of crack propagation) is suppressed when it beings to propagate thicknesswise, chordwise, spanwise, or in a combination of directions thereof. When a propagating crack encounters a ply in its path it either stops propagating or has to take "another" path to continue propagating. This taking of "another" path decreases the extent of crack propagation from one end of the fan blade to another and thereby increases the composite fan blade robustness by preventing large scale damage to the component. This method of arresting or mitigating crack propagation has the potential to increase damage tolerance of the fan blade under impact events including bird strike, fan blade-out, ice and hail conditions.

<FIG> depicts one exemplary method of shuffling of the wide and narrow plies within the composite fan blade. <FIG> represents a chordwise view of the same fan blade as the series of shuffles are made. Here too the arrows point to each incremental change in the interleaving of the plies with each shuffle. The progression in interleaving is indicated by cross-sectional views 3A1 through 3A4, with 3A1 being the fan blade without interleaving due to shuffling, while 3A4 is the fan blade after the last shuffle. <FIG> and <FIG> are shown again in expanded view for the benefit of the reader.

In view 3A1 of <FIG>, the suction surface <NUM> and the pressure surface <NUM> contact each other at the leading edge and trailing edge of the fan blade. The suction surface <NUM> and the pressure surface <NUM> comprise the widest plies 502A and 502B respectively. Located adjacent to the widest plies 502A and 502B (towards the center of the fan blade) are intermediate width plies 504A (hereinafter intermediate ply <NUM>) and 504B respectively, while the narrowest length ply <NUM> (hereinafter narrowest ply <NUM>) is located at the center of the fan blade. In view 3A1, the plies are sequentially arranged with the widest ply lying next to an intermediate ply, which lies next to the narrowest ply. Shuffling promotes a change in this size wise sequential distribution of the plies. The plies after shuffling staggered with no large size sequences (by ply size) in the fan blade.

In an embodiment, the narrowest ply is <NUM> to <NUM>% of the size of the widest ply, while an intermediate ply is always wider than the narrowest ply and has a length that varies from <NUM> to <NUM>% of the width of the widest ply.

While the <FIG> depicts only three ply lengths - the widest ply, the intermediate length ply and the narrowest ply, a composite fan blade may contain plies having <NUM> or more different lengths of plies based on the length of the widest ply. The Table below indicates <NUM> plies of different sizes based on the length (width) of the widest ply. The widest ply is Ply #<NUM>, while the narrowest ply is Ply # <NUM> in the Table. All <NUM> plies indicated in the Table below do not have to be used in a composite. Any combination of <NUM> or more plies of different lengths from the Table may be used and shuffled as desired to produce the best resistance to stress and delamination.

While the dimensions pertaining to ply size in the Table refer to the width of the plies, it can apply to any dimension such as, for example, length or thickness. In other words, the dimension of the smallest ply can be expressed as a percentage of that dimension of the longest ply - and that dimension can be width, length or thickness.

With reference now again to <FIG>, in a first shuffle seen in view 3A2, a portion of the widest plies 502A and 502B are shuffled to be in the center of the narrowest plies <NUM>, splitting the narrowest plies <NUM> into two domains 506A and 506B that contact the opposing surface of the newest portion of the widest plies 502C. The thickness of the widest plies 502A and 502B are reduced by the amount of ply material used in 502C, while the original central region <NUM> is now split into two regions 506A and 506B. The combined thickness of 506A and 506B is equal to that of the original central region <NUM>. With each shuffle, the thickness of the original plies is reduced. The reduction of thickness of a particular ply in one region is proportional to the increase of thickness of the particular ply in another region of the fan blade, thus maintaining a constant volume for the fan blade despite the displacement and rearrangement of the plies. As may be seen from the <FIG> (view 3A2), as a result of this first shuffle, there are now long plies interspersed with shorter plies.

In the second shuffle seen in view 3A3, the intermediate plies 504A and 504B are split (shuffled) into two more plies 504C and 504D that are disposed on and contact the widest ply 502C located in the center of the fan blade. The widest plies 502A, 502B and 502C are also split into two additional plies 502D and 502E that are dispersed amongst the narrowest plies 506A and 506B to produce plies 506C and 506D. With each shuffle, a previously existing thicker ply is narrowed and interspersed amongst plies of a different length. This as can be seen from the <FIG>, the various plies detailed in sequence from the suction surface <NUM> to pressure surface <NUM> are widest ply 502A, intermediate ply 504A, narrowest ply 506A, widest ply 502D, narrowest ply 506C, intermediate ply 504C, widest ply 502C, intermediate ply 504D, narrowest ply 506D, widest ply 502E, narrowest ply 506E, intermediate ply 504B and widest ply 502B. It can thus be seen that with each shuffle there is a greater dispersion of plies of different sizes and order of the plies is no longer sequential (i.e., an intermediate ply may be dispersed between two narrowest plies instead of being dispersed between the narrowest ply and the widest ply as seen in the FIG.

<FIG> (3A4) reflects one more shuffle and a greater mixing of the plies of different sizes. In the interests of brevity, the order of the plies will not be detailed one more time, but the reader can gamer that there is a greater dispersion of plies of different sizes amongst one another.

While the arrangement depicted in the <FIG> shows the dispersion in the thickness direction of the fan blade, this shuffling can also be conducted in the span direction of the blade. This results in interleaving where short plies being interspersed with long plies.

This dispersion and intermixing of plies based on ply size promotes weld and boundary lines between plies to be dispersed thus minimizing the possibility of continuous delamination (delamination across the entire fan blade) occurring along a ply boundary. <FIG> and <FIG> show how shuffling disperses not only the plies but also the boundary between plies. <FIG> depicts the prior art arrangement of plies in a conventional method of manufacturing the fan blade while <FIG> depicts the arrangement of plies and the boundary between plies when subjected to shuffling.

<FIG> depicts a portion of fan blade (viewed chordwise) proximate to the leading edge (LE) with suction surface <NUM> and pressure surface <NUM>. <FIG> depicts two enlarged sections <NUM> and <NUM> of the fan blade. The section <NUM> depicts the region around the leading edge (LE) of the fan blade, while the section <NUM> depicts the region proximate to the leading edge. From the two enlarged sections <NUM> and <NUM> it can be seen that disposed between the upper camber <NUM> and the lower camber <NUM> are a series of plies, notably the widest ply <NUM>, the intermediate ply <NUM> and the narrowest ply <NUM> (See <FIG> for details). Since there is no interleaving between the plies and the plies are often dropped in only direction, it gives rise to resin-rich areas called resin pockets. In the <FIG>, this is depicted by the resin-rich seam <NUM> at the mid-plane where the plies meet. The resin rich seam <NUM> is also called a ply drop. These ply drops occur because of the termination of plies at certain planar locations, to obtain the desired thickness reduction or taper. These ply drops <NUM> also serve as pathways for delamination between plies. In the <FIG> all of the ply drops of the individual plies align at the ply drop <NUM> to produce a major flaw line, which can lead to an easy delamination.

<FIG> depicts a portion of the fan blade <NUM> (viewed chordwise) proximate to the leading edge (LE) having upper camber <NUM> and loser camber <NUM> with interleaved plies contained therebetween. The <FIG> depicts two enlarged views <NUM> and <NUM> of the fan blade. View <NUM> is an enlarged sectional view of the region near the leading edge (LE), while view <NUM> depicts a section of the fan blade proximate to the leading edge. The interleaved plies are arranged as previously described in FIG. 3B (see views 3B3 and 3B4) and the interleaving process will not be detailed here once again. From the <FIG>, it may be seen that from the pressure surface to the suction surface of the fan blade, the plies are interleaved (in sequence) as follows - widest ply 702A, intermediate ply 704A, narrowest ply 706A, widest ply 702B, narrowest ply 706B, intermediate ply 704B, widest ply 702C, intermediate ply 704C, narrowest ply 706C, widest ply 702D, narrowest ply 706D, intermediate ply 704D and widest ply 702E.

Because of the interleaving of wider and narrower plies in the <FIG>, the ply drops (the resin rich regions) are spaced out and not aligned thus offering a crack an easy path of propagation which can eventually lead to complete delamination of a portion of the fan blade. Furthermore in the central region of the fan blade (i.e., the mid-plane region), the presence of a continuous ply 702C prevents the presence of a ply drop, which prevents the delamination of the fan blade. In summary, the interleaving of plies causes resin concentration to be reduced when compared with fan blades where there is no interleaving.

In one embodiment, one manner of manufacturing the fan blade comprises shuffling plies in a fan blade prior to contacting the plies with one another such that they form interleaved plies. As noted above, interleaving comprises distributing wide plies within narrow plies and short plies within long plies in the fan blade. The interleaving is defined as an actual intersection of a plurality of plies of different variable dimensions that extend in the chordwise direction with another plurality of plies of different variable dimensions that extend in the spanwise direction such that their respective longitudinal axes intersect with one another at angles of <NUM> to <NUM> degrees. After laying up the plies as prescribed above, the interleaved plies are cured in an autoclave or similar device. The shuffling of the plies and the positional sequences may be prescribed by a computer.

The interleaving of plies caused by shuffling extends the robustness of the fan blades because they create obstructions in the path of crack propagation. The presence of resin rich regions that offer fertile pathways for delamination are minimized. The plies can be interleaved to obtain a better balance of stress distribution across the fan blade.

In an embodiment, blade robustness is improved as measured by the extent of delamination when compared with a fan blade of the same dimensions that does not contain interleaved plies.

Claim 1:
A fan blade airfoil comprising:
interleaved plies (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) formed of fibers embedded in a matrix, where interleaving comprises distributing wide plies within narrow plies in the fan blade airfoil in a chordwise direction thereof and short plies within long plies in the fan blade airfoil in a spanwise direction thereof , wherein interleaving comprises shuffling short plies within long plies in the spanwise direction, wide plies within narrow plies in the chordwise direction and thick plies within thin plies in a thickness direction of the fan blade airfoil to avoid segregating plies of one particular dimension from plies of another particular dimension,
characterised in that:
the interleaving is defined as an actual intersection of a plurality of plies (<NUM>, <NUM>, <NUM>) of different variable dimensions that extend in the chordwise direction with another plurality of plies (<NUM>, <NUM>) of different variable dimensions that extend in the spanwise direction such that their respective longitudinal axes (AA', BB', CC') intersect with one another at angles (θ) of <NUM> to <NUM> degrees.