Patent Description:
Various structural components are used to form a typical aircraft. For example, wing and empennage surfaces of an aircraft typically include stringers that are coupled to skin members on the wing and empennage surfaces that cooperatively provide a desired flexural and torsional stiffness to the wing and empennage surfaces.

Aircraft structures may be formed from composite materials, which are generally reinforced polymer-based materials used in place of metals, particularly in applications in which relatively low weight and high mechanical strength is desired. Accordingly, composite materials are widely used in a variety of commercial and military aircraft, terrestrial vehicles and consumer products. A composite material may include a network of reinforcing fibers that are generally applied in layers, and a polymeric resin that substantially wets the reinforcing fibers to form a binding contact between the resin and the reinforcing fibers. The composite material may then be formed into a structural component by a variety of known forming methods, such as an extrusion process or other forming processes.

In an aircraft, a stringer may be used to transfer bending loads in skin panels, and stiffen the skin panels in order to prevent buckling, for example. The stringers and skin panels may be made of composite materials, such as carbon fiber reinforced plastic (CFRP). A composite stringer may be fabricated from multiple plies of reinforcing fibers.

Often, composite parts, such as composite stringers, include one or more portions having at least some degree of curvature. Composite parts with even a slight curvature are difficult to construct with <NUM>° uniaxial fiber tape, because the plies within the tape are unable to stretch to comply with long aspect ratio contours.

<CIT> discloses systems and methods relating to composite lamination using one or more arrays or parallel material dispensing heads. A first strip material is applied to a work surface datum at a first angle with a first material dispenser, and a plurality of second strip materials are then applied to a work surface datum each at a second angle with a plurality of rotatable parallel material dispensers. The application of the strip materials is continued by the rotatable parallel material dispensers until a desired length is reached.

<CIT> discloses, according to its abstract, "A prepreg base material includes reinforcing fibers arranged substantially in one direction and a matrix resin between the reinforcing fibers, wherein the prepreg base material has substantially throughout its entire surface incisions, each incision extending in a direction substantially crossing the reinforcing fibers, wherein substantially all of the reinforcing fibers are divided by the incisions, a length (L) of each of reinforcing fiber segments formed by the incisions is in the range of <NUM> to <NUM>, a thickness H of the prepreg base material is in the range of <NUM> to <NUM> mum, and a fiber volume content by Vf of the reinforcing fibers is in the range of <NUM> to <NUM>%.

Current methods of forming contoured stringers, such as with fiber tape, generate wrinkles on or in the stringers. For example, draping a composite membrane assembly, which includes multiple layers of plies, along a contoured (that is, curved, non-straight) surface causes the plies to stretch and/or compress. When the plies are forced to stretch, bridging and resin pooling may result. On the other hand, when the plies are forced to shrink, wrinkles may be formed. In both stretching and shrinking situations, inspection and repair costs increase.

A known method of using fiber tape to form or otherwise conform to curved surfaces includes forming <NUM>° cuts in the fiber tape, and overlapping plies to maintain strength. The cuts are <NUM>° (that is, perpendicular) to a <NUM>° direction of the fiber tape. In particular, the cuts are perpendicular to a longitudinal plane of the fiber tape. By forming the cuts and overlapping portions of the tape, however, the fiber tape increases in thickness, weight, and complexity. Further, the overlapped portions form bumps in the fiber tape. Additionally, while the <NUM>° cuts provide a certain amount of flexibility to the fiber tape, they do not overcome the problems of shrinking and compression. Consequently, such a method does is still susceptible to wrinkling.

Overall strength of a composite part decreases with an increase in the number of wrinkles. Indeed, it has been found that wrinkles in a composite part may reduce strength of the part by <NUM>% or more.

When used to form a flat surface, a composite membrane assembly generally lays flat without wrinkling. As the composite membrane assembly is laid up to form a flat surface or folded over a <NUM>° edge (for example, a single curvature shape), there generally is little or no tension or compression in the membrane, and therefore the composite membrane assembly does not wrinkle. However, as noted, when used to form an arcuate, curved surface (for example, a double curvature shape), the composite membrane assembly is influenced by compression and/or tension, and therefore wrinkles.

Thus, a need exists for an improved system and method of forming a composite material that is able to stretch to accommodate curved surfaces without wrinkling, while substantially maintaining strength.

Certain embodiments of the present disclosure provide a composite ply configured to form a composite membrane assembly along with a plurality of other composite plies. The composite ply may include a main body of reinforced fibers connected together with a resin, wherein the main body includes a base connected to an opposed boundary surface through opposed ends and opposed sides. At least one non-orthogonal cut is formed through a thickness of the main body from the base to the boundary surface. The non-orthogonal cut(s) may be staggered with respect to at least one other non-orthogonal cut of an adjacent composite ply so that the non-orthogonal cut(s) does not form a contiguous linear cut with the other non-orthogonal cut(s) of the adjacent composite ply. The non-orthogonal cut may form a non-orthogonal angle with respect to a longitudinal plane of the composite ply. The longitudinal plane may extend between opposed ends and may be parallel with one or both of the base and the opposed boundary surface.

In at least one embodiment, the non-orthogonal angle may be at least <NUM>° and no more than <NUM>°. In particular, the non-orthogonal angle may be at least <NUM>° and no more than <NUM>°.

The non-orthogonal cut(s) may form ply segments that are spliced together. In at least one embodiment, the composite ply includes a plurality of non-orthogonal cuts. The plurality of non-orthogonal cuts may all be formed at the same angle. In at least one other embodiment, at least two of the non-orthogonal cuts may be formed at different angles. Further, at least two of the non-orthogonal cuts may be oriented in different directions.

According to claim <NUM>, the present disclosure provide a composite membrane assembly that includes a plurality of stacked composite plies. Each of the stacked composite plies includes a main body of reinforced fibers connected together with a resin. The main body includes a base connected to an opposed boundary surface through opposed ends and opposed sides. A longitudinal plane extends between the opposed ends and is parallel with one or both of the base and the opposed boundary surface. A plurality of non-orthogonal cuts are formed through a thickness of the main body from the base to the boundary surface. The plurality of non-orthogonal cuts form a non-orthogonal angle with respect to the longitudinal plane of the composite ply. The plurality of non-orthogonal cuts of one of the composite plies are opposite from the plurality of non-orthogonal cuts of an adjacent composite ply. The plurality of non-orthogonal cuts may be staggered with respect to the plurality of non-orthogonal cuts of an adjacent composite ply so that the non-orthogonal cuts do not form a contiguous linear cut with the other non-orthogonal cuts of the adjacent composite ply.

Certain embodiments of the present disclosure provide, according to claim <NUM>, a method of forming a composite membrane assembly according to claim <NUM>.

The foregoing summary, as well as the following detailed description of certain embodiments will be better understood when read in conjunction with the appended drawings. Moreover, unless explicitly stated to the contrary, embodiments "comprising" or "having" an element or a plurality of elements having a particular property may include additional elements not having that property.

Certain embodiments of the present disclosure provide a method of forming plies of composite membrane assemblies through staggered (for example, nonoverlapping) angular cuts. The angular cuts may be non-orthogonal. For example, the angular cuts may be between <NUM>°-<NUM>° in relation to the <NUM>° direction of each ply. It has been found that an angular cut of <NUM>°-<NUM>° may provide a suitable combination of increased flexibility and relatively low loss in strength. It has been found that such angular cuts increase flexibility or stretch by, for example, <NUM>%, while only impacting tape strength by less than <NUM>%, for example.

Embodiments of the present disclosure provide composite plies that include angular cuts that are spread across a relatively long distance (so that each cut is not concentrated at a particular location along a length of the ply), thereby allowing neighboring plies in other orientations to pick up the load through shear. As such, weight may be reduced, and undesirable thickness caused by bumps may be eliminated, minimized, or otherwise reduced.

Certain embodiments of the present disclosure provide composite plies that may be used to form a composite membrane assembly (such as a composite fiber tape, or the like) that may include intermittent angular cuts that are configured to accommodate curvature. The angular cuts accommodate curved surfaces in layups by eliminating or otherwise reducing wrinkles and bumps caused by overlaps.

Certain embodiments of the present disclosure provide a composite laminate structure having multiple plies. The composite laminate structure may include alternating layup of axial and non-axially oriented unidirectional fiber plies. Each axially oriented ply may have a fiber direction in line with a longitudinal axis of the axially oriented ply. Each non-axially oriented ply may have a fiber direction other than a longitudinal axis of the non-axially oriented ply. Angular cuts may be formed in each ply. The angular cuts may be non-orthogonal with respect to a longitudinal axis of each ply. The angular cuts facilitate arcuate or curved contours without buckling or creating voids during a layup or curing process. The angular cuts in adjacent plies may not overlap. Instead, the angular cuts in adjacent plies are staggered or offset with respect to one another. Further, the angle of each angular cut may be the same or different. For example, a first set of angular cuts may be at <NUM><NUM>, a second set of cuts may be at <NUM>°, a third set of cuts may be at -<NUM>°, a fourth set of cuts may be at -<NUM><NUM>, and so on. As recited in claim <NUM>, angular cuts in adjacent plies are opposite from one another. In at least one embodiment, the cuts may be between <NUM>° and <NUM>° with respect to the longitudinal axis of a ply.

Embodiments of the presently claimed invention provide composite membrane assembly that may be used to form various composite structures for an aircraft. For example, embodiments of the present disclosure may be used to form a composite stringer. A composite stringer may be fabricated from multiple plies of reinforcing fibers. Some plies have reinforcing fibers oriented at <NUM>° with respect to an axis of primary loading. As such, these fibers are configured to transfer uniaxial loads. Other plies have reinforcing fibers oriented at +/- <NUM>° or +/- <NUM>° to transfer shear, transverse, and bearing loads. Accordingly, a stringer may be formed of multiple composite plies, each of which may be configured to transfer uniaxial or shear, transverse and bearing loads. Layers of composite plies may form a composite membrane assembly, which may be used to form a stringer, rib, spar, skin panel, and the like.

<FIG> is a diagrammatic representation of a lateral view of an aircraft <NUM>. The aircraft <NUM> may include a plurality of major assemblies, each of which may be formed of composite materials, which may include composite plies. The major assemblies of the aircraft <NUM> may include a fuselage <NUM>, wing assemblies <NUM>, and empennage <NUM>. One or more propulsion units <NUM> may be coupled to the wing assemblies <NUM>, the fuselage <NUM>, and/or other portions of the aircraft <NUM>.

<FIG> is a schematic illustration of an aircraft <NUM> having major aircraft assemblies <NUM>, <NUM>, and <NUM>. Referring to <FIG>, each of the assemblies <NUM>, <NUM> and <NUM> may include skin panels <NUM> and stiffeners. The stiffeners are configured to prevent the major assemblies <NUM>, <NUM> and <NUM> from buckling. For example, the stiffeners may be configured to transfer bending loads in the skin panels <NUM>, and stiffen the skin panels <NUM> so that the panels <NUM> do not buckle under loading. It is to be understood that the stiffeners are not limited to the major aircraft assemblies <NUM>, <NUM> and <NUM>. Indeed, stiffeners may be used in any aircraft structures that are to be stiffened.

A stringer is an example of a stiffener. Stringers <NUM> in the fuselage <NUM> may be subject to uniaxial tension and compression and out-of-plane buckling. The fuselage stringers <NUM> may also be subject to secondary loads including shear and bearing loads.

Each wing assembly <NUM> may include upper and lower stringers <NUM>. The upper stringers <NUM> may be subject to uniaxial compression, while the lower stringers <NUM> may be subject to uniaxial tension (the primary loading is sometimes reversed). The upper and lower stringers <NUM> may also be subject to secondary loads including shear, bearing, and transverse loads.

The empennage <NUM> includes horizontal and vertical stabilizers. The stringers <NUM> in the stabilizers may be subject to similar primary and secondary loading as the wing assemblies <NUM>.

A component under compression tends to twist, cripple and buckle. The stringer <NUM> provides strength, resists compression and tension, and provides stability against twist, cripple and buckle. For example, the stringer <NUM> provides a support structure within the component that may brace against various exerted forces.

<FIG> is a diagrammatic representation of an end view of a skin panel <NUM> and stringer <NUM>. The stringer <NUM> is an example of a stringer <NUM>, described with respect to <FIG>. As shown in <FIG>, the stringer <NUM> has an I-beam geometry. The stringer <NUM> may include a web <NUM> between first and second flanges <NUM> and <NUM>. The web <NUM> has a depth D that provides a desired resistance to an applied loading.

The first and second flanges <NUM> and <NUM> may be generally planar members. The first flange <NUM>, which may be referred to as a cap, has a width W<NUM>. The second flange <NUM>, which may be referred to as a base, has a width W<NUM>. The web <NUM>, cap <NUM> and base <NUM> extend in an X-direction along an X-axis (which is normal to the drawing sheet shown in <FIG>). The X-axis is the axis of primary loading. The web <NUM>, cap <NUM> and base <NUM> may have constant widths along the X-direction, or they may vary continuously or even non-continuously along the X-direction.

<FIG> also shows a coordinate system for each of the web <NUM> (X-Yw-Zw), cap <NUM> (X-Yc-Zc), and base <NUM> (X-Yb-Zb). The coordinate systems may correspond to an I-beam formed by back-to-back C-channels. Orientations of all reinforcing fibers may be measured with respect to the X-direction.

A stringer <NUM> herein is not limited to the I-beam geometry illustrated in <FIG>. Other usable geometries include, but are not limited to Z-beams, blades, C-channels, and hat beams. Stringers having such geometries may include at least one web and base. Examples of hat, Z-beam and C-Channel geometries <NUM>, <NUM> and <NUM>, respectively, are illustrated in <FIG>.

Referring again to <FIG>, the skin panel <NUM>, which has a thickness T<NUM>, is coupled to the base <NUM>. In at least one embodiment, the base <NUM> may be adhesively bonded to the skin panel <NUM>. In at least one other embodiment, the base <NUM> may be co-cured with the skin panel <NUM>.

The base <NUM> may be clamped to the skin panel <NUM> by fasteners <NUM>. The fasteners <NUM> extend through apertures in the skin panel <NUM> and the base <NUM>. The fasteners <NUM> are engaged by nuts <NUM> to impart a predetermined compressive force to the skin panel <NUM> and the base <NUM>. The fasteners <NUM> may be used instead of, or in addition to, adhesive bonding.

Fasteners for clamping the stringers <NUM> to the skin panels <NUM> are not limited to bolts <NUM> and nuts <NUM>. Other examples of fasteners include staples, z-pins, rivets, swage fasteners, and barbs. While fasteners such as bolts <NUM> extend entirely through a stringer base <NUM> and skin panel <NUM>, fasteners such as staples, z-pins and barbs may extend partially into the skin panels. Fasteners such as staples, z-pins and barbs may be integral with the stringer bases.

In at least one embodiment, the stringers <NUM> may be secured to the skin panels <NUM> through stitching. Plies of fibers may be stitched together. Stitches may be threaded through apertures in a layup of dry composite plies. Resin is then infused in the structure, and the structure is cured.

The skin panel <NUM> may include a stack of plies of reinforcing fibers embedded in a matrix. Different plies may have fibers oriented at <NUM>°, <NUM>°, -<NUM>° and <NUM>°, for example. Some embodiments may have a quasi isotropic layup, whereby equal amounts and percentages of <NUM>°, <NUM>°, -<NUM>° and <NUM>° degree plies are used. In other embodiments, the different plies may include reinforcing fibers oriented at <NUM>°, -<NUM>°, <NUM>° and -<NUM>°, or some other angles or combinations. The reinforcing fibers in the skin panels <NUM> may be carbon fibers having an intermediate modulus of <NUM> MSI (megapounds per square inch). Ply stiffness of the skin panel <NUM> (for example, a stiffness of the carbon fibers plus resin) may have a modulus of <NUM>-<NUM> MSI. Stack stiffness along <NUM>° may be <NUM>-<NUM> MSI. One MSI is equivalent to <NUM> Gpa.

The stringer <NUM> may include multiples plies of reinforcing fibers embedded in a matrix. The reinforcing fibers and matrix are not limited to any particular composition. Examples of the fibers include carbon fibers, glass fibers, aramid fibers, boron fibers, and titanium fibers. Examples of the matrix include plastic and metal. As another example, carbon fibers may be embedded in a plastic matrix. As yet another example, carbon fibers may be embedded in a titanium matrix. In some embodiments, the carbon fibers may have an intermediate modulus of <NUM> MSI, and ply stiffness may be <NUM>-<NUM> MSI.

Other types of stiffeners include spars and ribs. The stringers, spars, and ribs may form a frame of an aircraft, while skin panels are formed around the formed frame. Each of the stiffeners and skin plates may be formed from one or more composite membrane assemblies, each of which is formed by a plurality of stacked composite plies. The composite plies and the composite membrane assemblies may be formed as described below.

<FIG> is a diagrammatic representation of a lateral view of a composite ply <NUM> useful to understand the invention. The composite ply <NUM> may be used to form a composite membrane assembly, which may be used to form various structures (for example, stiffeners, ribs, spars, and skin panels of an aircraft), such as any of those described above. For example, the composite ply <NUM> may be sandwiched together with other composite plies to form a composite membrane assembly, which may then be used to form a stringer. In at least one embodiment, the composite membrane assembly may be used to form pre-preg or fiber tape, for example.

The composite ply <NUM> may be formed as a flat, planar sheet, for example, of reinforced fibers bonded together with a resin. As described below, one or more angled cuts may be formed in the composite ply to increase flexibility of the composite ply <NUM> without substantially reducing strength of a composite membrane assembly formed by a plurality of the composite plies <NUM>.

The composite ply <NUM> includes a main body <NUM> that may be formed by or otherwise include a plurality of reinforced fibers <NUM>. The reinforced fibers <NUM> may couple together through a resin, such as a glue, matrix, epoxy, liquid plastic, or the like, that is used to laminate the fibers <NUM> together. More or less fibers <NUM> may be used to form the composite ply <NUM>. For example, the composite ply <NUM> may be formed from <NUM> or more reinforced fibers. Optionally, the composite ply <NUM> may be formed from more or less reinforced fibers.

The composite ply <NUM> includes a base <NUM> connected to an opposite boundary surface <NUM> (for example, a top surface as shown by the orientation of the composite ply <NUM> in <FIG>) through opposed ends <NUM> and <NUM> and opposed sides <NUM> (only one side is shown in <FIG>). A longitudinal plane <NUM> extends through a length of the composite ply between the ends <NUM> and <NUM>. The longitudinal plane <NUM> is shown extending through a center of the composite ply <NUM>. However, the longitudinal plane <NUM> may be with respect to any level of the composite ply <NUM>. The longitudinal plane <NUM> may generally be coplanar with the base <NUM> and the boundary surface <NUM>. The longitudinal plane <NUM> is parallel to a length L of the composite ply <NUM>. The length of a composite membrane assembly formed by a plurality of stacked composite plies may be referred to as a warp. A width of the composite membrane assembly (from side-to-side) may be referred to as a fill. The longitudinal plane is along a <NUM>° direction of the fibers <NUM>, in that the fibers <NUM> may extend in parallel direction to the length L. As shown, each fiber <NUM> may have a length that extends between the ends <NUM> and <NUM>. Alternatively, one or more of the fibers <NUM> may have a length that extends in another direction, such as cross-wise to the length L.

The composite ply <NUM> may have a thickness t. For example, the thickness t may be <NUM>" thick. In at least one other embodiment, the thickness t may be greater or lesser than <NUM>" thick.

As shown, an angled cut <NUM> is formed through the composite ply <NUM> from the boundary surface <NUM> to the base <NUM>. The cut <NUM> may be angled with respect to the longitudinal plane <NUM> (or the <NUM>° direction) at an angle α, which may be non-orthogonal. That is, the angle α may be other than <NUM>° with respect to the longitudinal plane <NUM> (or the <NUM>° direction), or other than parallel to the longitudinal plane <NUM>. In at least one embodiment, the angle α may exceed <NUM>° and be less than <NUM>°. For example, the angle α may be <NUM>° in relation to the longitudinal plane <NUM> (or the <NUM>° direction). As another example, the angle α may be <NUM>° in relation to the longitudinal plane <NUM> (or the <NUM>° direction). It has been found that an angle α from <NUM>°-<NUM>° provides the composite ply <NUM> with a unique combination of increased flexibility and low loss of strength.

The angled cut <NUM> is formed by a straight, linear cut from the boundary surface <NUM> to the base <NUM>. In this manner, the angled cut <NUM> is not concentrated in any one plane <NUM> that is perpendicular to the longitudinal plane <NUM>. As such, the angled cut <NUM> is not concentrated at any one point, plane, or edge within or on the composite ply <NUM>. Instead, the angled cut <NUM> is dispersed over a distance d that is substantially longer than a thickness p of the plane <NUM>. As shown, the angled cut <NUM> is dispersed over the distance d that may be more than fifty times the thickness p of the plane <NUM>. Optionally, the distance d may be less than fifty times the thickness p. For example, the distance d may be ten times the thickness p.

The distance d is inversely proportional to the absolute value of the magnitude of the angle α. For example, as the angle α increases, the distance d decreases. Accordingly, a smaller angle α provides an angled cut <NUM> that is dispersed over a longer distance d. Conversely, a greater angle α provides an angled cut <NUM> that is dispersed over a shorter distance d.

The angled cut <NUM> separates the composite ply <NUM> into separate segments <NUM> and <NUM> that are spliced together, such as through resin, at the interface of the angled cut <NUM>. While the composite ply <NUM> is shown having a single angled cut <NUM>, more angled cuts may be used.

The angled cuts <NUM> provide a degree of flexibility (that is, an ability to be stretched, pulled, or compressed in longitudinal directions that are parallel to the length L, and/or bent in directions relative to the length L) to the composite ply <NUM>. For example, a typical piece of pre-preg tape has no flexibility. However, by forming the pre-preg from composite plies such as shown in <FIG>, some degree of flexibility may be gained. For example, it has been found that the angled cuts <NUM> may increase flexibility of the composite ply <NUM> by at least <NUM>%, upwards of <NUM>%, <NUM>%, or even more. In short, each angled cut <NUM> formed within a composite ply <NUM> may increase flexibility of the composite ply <NUM>. At the same time, because the angled cuts <NUM> are dispersed over a relatively long distance (that is, not concentrated at or within a plane <NUM> that is perpendicular to the longitudinal plane <NUM>), the composite ply <NUM> when stacked with other composite plies <NUM> having angled cuts that do no overlap, provides a composite membrane assembly (such as a membrane of pre-preg tape) that lose little, if any, strength. In contrast, the inventor has determined that a composite membrane assembly including composite plies that have vertically aligned perpendicular cuts at the same location are susceptible to tearing apart at the areas of the aligned perpendicular cuts. The inventor has found that a composite membrane assembly formed of composite layers having angled cuts that do not overlap with one another (but are, instead, staggered) increase the flexibility of the composite membrane assembly by at least <NUM>%, while retaining strength similar to that of an uncut composite membrane assembly, such as <NUM>% of the strength.

As noted, the angled cut <NUM> may be at an angle other than what is shown in <FIG>. For example, the angle α of the angled cut <NUM> may be <NUM>°, similar to that shown in <FIG>. It has been found that an angle α of <NUM>°-<NUM>° provides an increased combination of flexibility and strength (with the combination quantified, for example, as a sum of a percentage of ability to flex and a percentage of retained strength in relation to an uncut piece of composite material). Alternatively, the angle α may be various other angles, such as <NUM><NUM>, <NUM>°, or the like. Indeed, the angle α may be any non-orthogonal angle. That is, the angle α may be any angle other than <NUM>° or <NUM>° with respect to the longitudinal axis <NUM>. While an angle of <NUM>° disperses the angular cut over a great distance d (and therefore increases an overall strength of a composite membrane assembly), it also provides a reduced flexibility as compared to an angle that is greater than <NUM>°. Conversely, while an angle of <NUM>° may have an increased flexibility as compared to an angle of <NUM>°, the angle of <NUM>° exhibits decreased strength in comparison to an angle of <NUM>°. In short, the strength of the composite ply <NUM> may be inversely proportional to the absolute value of angle α, while the flexibility of the composite ply <NUM> may be directly proportional to the absolute value of the angle α. Note, the angle α may be measured from <NUM>° to <NUM>°, and negative values of angles therebetween (as shown with respect to <FIG>, for example). For example, an angle α that may be considered <NUM>° is -<NUM>° (as shown in <FIG>, for example). Again, it has been found that an angle α in the range of <NUM>° to <NUM>°, or -<NUM>° to -<NUM>°, provides an increased combination of flexibility and strength.

Additionally, each of the ends <NUM> and <NUM> may be cut or otherwise formed at an angle, such as a non-orthogonal angle. If, for example, a structure is to be formed having a plurality of composite plies <NUM>, some of which are shorter than others, <NUM>° ends may form an abrupt step between adjacent plies. That is, <NUM>° ends may cause steps in a layup. The steps may cause a wrinkle in the structure. As such, the ends <NUM> and <NUM> may be angled to disperse such a step over a greater distance, in the same manner that the angled cut <NUM> disperses the cut over a relatively long distance.

<FIG> is a diagrammatic representation of a lateral view of angled cuts <NUM>, <NUM>, <NUM>, and <NUM> formed in composite plies <NUM>, useful to understand the invention. Note, each angled cut line (including the dashed line) is intended to show an angled cut in a different composite ply <NUM>, not the same composite ply <NUM>. As shown, the angled cuts may be formed at different locations of each composite ply <NUM>. Therefore, when the composite plies <NUM> are stacked together (such as a base <NUM> of one composite ply being supported by an upper boundary surface <NUM> of another composite ply <NUM>), the angled cuts <NUM>, <NUM>, <NUM>, and <NUM> are staggered with respect to one another so that they do not completely align or otherwise overlay one another. Further, in the stacked orientation, the angled cuts <NUM>, <NUM>, <NUM>, and <NUM> do not directly connect together to form a single contiguous cut that extends through adjacent composite plies <NUM>. At least portions of each angled cut <NUM>, <NUM>, <NUM>, and <NUM> may not overlap portions of other angled cuts <NUM>, <NUM>, <NUM>, and <NUM> of stacked composite plies <NUM>.

For example, as shown in <FIG>, each of the angled cuts <NUM>, <NUM>, <NUM>, and <NUM> may be formed at the same angle α from a boundary surface <NUM> to a base <NUM>. However, the terminal ends of each angled cut <NUM> do not align at the same points. Instead, the angled cut <NUM> extends from between a first base point <NUM> to a first boundary point <NUM> that is offset or shifted from a second base point <NUM> and a second boundary point <NUM>, respectively, of the angled cut <NUM>. The other angled cuts <NUM> and <NUM> may be offset or shifted in a similar manner. As such, when the composite plies <NUM> are stacked together, the terminal ends of each angled cut <NUM>, <NUM>, <NUM>, and <NUM> may not overlap or connect with one another, but, instead, may be staggered. For example, terminal ends of each of the angled cuts <NUM>, <NUM>, <NUM>, and <NUM> do not abut into or otherwise form a contiguous cut with a terminal end of any other of the angled cuts.

By staggering the angled cuts <NUM>, <NUM>, <NUM>, and <NUM> of composite plies <NUM> of a stacked composite membrane assembly, the strength of the overall composite membrane assembly is substantially retained, due to the fact that a single contiguous cut is not formed unimpeded through a thickness of a composite membrane assembly formed by the stacked composite plies <NUM> or through adjacent composite plies <NUM>. It has been found that staggering the angled cuts in such a manner leads to a stacked composite membrane assembly that retains <NUM>% or more of its strength (that is, <NUM>% of the strength of a composite membrane assembly formed of plies having no cuts). At the same time, the angled cuts provide the stacked composite membrane assembly with flexibility that allows the stacked composite membrane assembly to form or otherwise conform to a curved shape without wrinkling.

One or more cover plies <NUM> may wrap around portions of the composite plies <NUM> or a stacked composite membrane assembly formed of multiple composite plies <NUM> at areas where each composite ply <NUM> is cut. The cover pl(ies) <NUM> provide a bracing support that prevents or otherwise reduces the risk of the segments between angled cuts from separating. If, for example, the angled cuts formed in a plurality of composite plies reduce the strength of a stacked composite membrane assembly by <NUM>%, the cover pl(ies) <NUM> may strengthen the stacked composite membrane assembly so that it has <NUM>% (or closer to <NUM>%) of the strength of a stacked composite membrane assembly formed of uncut composite plies.

<FIG> is a diagrammatic representation of a lateral view of a composite ply <NUM>, useful to understand the invention. The composite ply <NUM> is similar to those described above. Angled cuts <NUM>, <NUM>, <NUM>, and <NUM> are formed at different locations within the composite ply. The angled cut <NUM> may be at an angle θ, while the angled cut <NUM> may be at an angle Φ that differs from the angle θ. The angled cut <NUM> may be at an angle -θ, which is opposite from the angle θ, while the angled cut <NUM> may be at an angle -Φ, which is opposite from the angle Φ. More or less angled cuts may be formed in the composite ply. Further, each angled cut may be at another angle than shown. Moreover, the angles <NUM> and <NUM> may be angles other than -θ and -Φ. The magnitude and direction of each angle may be based on a desired curvature of a structure to be formed by a plurality of stacked composite plies. For example, angled cuts of increased magnitude in one direction may be used to form a structural segment having an increased curvature in a particular direction. As another example, angled cuts of decreased magnitude in one direction may be used to form a structural segment having a reduced curvature in a particular direction. As noted, each composite ply that forms a composite membrane assembly may have angled cuts that are staggered with respect to one another.

<FIG> is a diagrammatic representation of a lateral view of a composite ply <NUM>, useful to understand the invention. As shown, the composite ply <NUM> includes a plurality of angled cuts <NUM> that regularly repeat. For example, a distance x between neighboring cuts may be the same between all neighboring cuts. Alternatively, the distance between angled cuts may be different among different sets of neighboring cuts. Moreover, the angle of each angled cut may be the same or different. As shown, a terminal end <NUM> of the composite ply <NUM> may include a ramped surface formed by an angled cut.

<FIG> is a diagrammatic representation of a lateral view of a stacked composite membrane assembly <NUM>, the specific illustrated arrangement of which is not covered by the appended claims, formed by a plurality of composite plies <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. As shown, the angled cuts <NUM> of adjacent plies <NUM>-<NUM> may not overlap with one another. Instead, the angled cuts <NUM> of neighboring plies <NUM>-<NUM> may be staggered or otherwise offset with respect to one another. The stacked composite membrane assembly <NUM> may include more or less composite plies than shown. Notably, none of the angled cuts <NUM> between adjacent composite plies <NUM>-<NUM> abut one another so as to form a contiguous cut between adjacent plies <NUM>-<NUM>.

<FIG> is a diagrammatic representation of a lateral view of a stacked composite membrane assembly <NUM> formed by a plurality of composite plies <NUM> and <NUM>, according to claim <NUM>. For the sake of simplicity, only two plies <NUM> and <NUM> are shown in <FIG>. It is to be understood, however, that the stacked composite membrane assembly <NUM> may be formed from more composite plies than shown.

The composite ply <NUM> includes a plurality of angled cuts <NUM>, while the composite ply <NUM> includes a plurality of angled cuts <NUM>. More or less angled cuts <NUM> and <NUM> may be formed in the composite plies <NUM> and <NUM>, respectively. Further, the angled cuts <NUM> and <NUM> may be formed at other non-orthogonal angles than shown.

The angled cuts <NUM> are oriented in a first direction in that they are canted toward an end <NUM>. In contrast, the angled cuts <NUM> are oriented in a second direction that is opposite from the first direction in that they are canted toward an end <NUM>. As shown, the orientation of the angles may alternate between adjacent composite plies <NUM> and <NUM>, such that the angled cuts of the composite ply <NUM> are opposite to those of the composite ply <NUM>. In at least one other embodiment, at least some neighboring angled cuts in the same composite ply may alternate in different directions, and may be in an inverse relationship with respect to angled cuts of an adjacent composite ply.

<FIG> is a diagrammatic representation of a lateral view of a formed stacked composite membrane assembly <NUM>, useful to understand the invention. The stacked composite membrane assembly <NUM> includes a first curved segment <NUM> having a first curvature. The first curved segment <NUM> connects to a second curved segment <NUM> having a second curvature that exceeds that of the first curvature <NUM>. For example, the first curved segment <NUM> may be a mild double curved surface, while the second curved segment <NUM> may be a high degree double curved surface. The second curved segment <NUM> connects to a first flat segment <NUM>, which, in turn connects to a second flat segment <NUM> at a right angle (which is a simple folded surface). Each segment <NUM>, <NUM>, <NUM>, and <NUM> may be formed by multiple composite plies.

Each of the composite plies of the first curved segment <NUM> may include a plurality of angled cuts separated a first distance from one another. The angled cuts of adjacent composite plies may be staggered. The composite plies of the second curved segment <NUM> may include a plurality of angled cuts separated a second distance from one another. In one embodiment, the second distance is shorter than the first distance, as the curvature of the second curved segment exceeds that of the first curved segment <NUM>. As such, the second curved segment <NUM> may include a greater number of angled cuts at closer distances, which facilitates a curvature of increased magnitude. Optionally, the angle of the cuts may be adjusted (as noted above) to accommodate the curvatures. In short, the number of staggered angled cuts in composite plies that form a particular portion of a composite membrane assembly may be directly proportional to an amount of curvature of the particular portion of the composite membrane assembly. That is, the number of angled cuts in each ply may increase as the degree of curvature increases.

The first and second flat segments <NUM> and <NUM> may be formed by a plurality of composite plies having no cuts formed therein. Because the first and second flat segments <NUM> and <NUM> do not include any double curved surfaces, there is little or no risk of the segments <NUM> and <NUM> wrinkling, for example. As such, the flat segments <NUM> and <NUM> may be devoid of formed cuts.

<FIG> is a diagrammatic representation of a top perspective view of a composite material <NUM> being folded along a linear edge <NUM>. The linear edge <NUM> is straight and the composite material <NUM> may be folded about the linear edge in the direction of arc <NUM>. Because the composite material <NUM> is folded with respect to the straight, linear edge <NUM>, the composite material <NUM> does not stretch and strain with respect to a direction <NUM> that is parallel to the linear edge <NUM>. As such, the composite material <NUM> may be formed of composite plies that do not have cuts formed therein, as there is little or no risk of the composite material <NUM> wrinkling.

<FIG> is a diagrammatic representation of a top perspective view of a composite material <NUM> having a single curved surface <NUM>. The composite material <NUM> curves with respect to a single arcuate direction <NUM>. Because the composite material <NUM> curves with respect to a single direction <NUM>, the composite material <NUM> does not stretch and strain with respect to a direction <NUM> that is parallel to its length. As such, the composite material <NUM> may be formed of composite plies that do not have cuts formed therein, as there is little or no risk of the composite material <NUM> wrinkling.

<FIG> is a diagrammatic representation of a top perspective view of a composite material <NUM> folded along a curved edge <NUM>. The curved edge <NUM> has an arcuate shape that may stretch and strain the composite material <NUM> along its length in the direction of arc <NUM>. Accordingly, the composite material <NUM> may be susceptible to wrinkling, for example. In order to control, eliminate, minimize, or otherwise reduce such wrinkling, the composite material <NUM> may be formed of plies having a plurality of angled cuts, as described above. The angled cuts of adjacent composite plies may be staggered.

<FIG> is a diagrammatic representation of a top perspective view of a composite material <NUM> having a double curved surface <NUM>. The double curved surface <NUM> curves with respect to the length <NUM> and width <NUM> of the composite material <NUM>. As such, the composite material <NUM> may be susceptible to wrinkling, for example. In order to control, eliminate, minimize, or otherwise reduce such wrinkling, the composite material <NUM> may be formed of plies having a plurality of angled cuts, as described above. The angled cuts of adjacent composite plies may be staggered.

<FIG> is a diagrammatic representation of a top perspective view of a composite material <NUM> having a jogged and curved transition edge <NUM>. As shown, the composite material <NUM> may have a complex shape of various curves in different directions. The composite material <NUM> shears and stretches. In order to control, eliminate, minimize, or otherwise wrinkling, the composite material <NUM> may be formed of plies having a plurality of angled cuts, as described above. The angled cuts of adjacent composite plies may be staggered.

<FIG> illustrates a flow chart of a method of forming a composite membrane assembly. At <NUM>, a plurality of composite plies are formed. One or more of composite plies may include reinforced fibers coupled together through resin, for example. Each composite play may be a planar sheet having a warp, fill, and thickness. Optionally, each composite ply may be akin to a string or ribbon having a warp and thickness, but minimal fill.

At <NUM>, it is determined if a portion of one or more of the composite plies is to form a double curved surface. If not, the method proceeds to <NUM>, in which no cut is formed through the portion of the composite ply.

If, however, the portion of each composite ply is to form a curved surface, the method proceeds from <NUM> to <NUM>, in which at least one angled cut is formed in the portion of the composite ply. Then, at <NUM>, the composite plies are stacked together so that the angled cut(s) of adjacent composite plies are staggered with respect to one another.

Composite membrane assemblies are formed by a plurality of stacked composite plies. The invention relates to a composite membrane assembly as defined in claim <NUM>. The composite membrane assemblies may be used to form various structures of an aircraft, for example, such as stiffeners and skin panels. Angled cuts may be formed in each of the composite plies. The angled cuts of the stacked composite plies may be staggered in relation to one another. The angled cuts of the composite plies provide a degree of flexibility to a composite membrane assembly, while the staggered relationship among cuts of stacked composite plies substantially maintains the strength of the composite membrane assembly (in relation to a membrane having plies that are uncut). The angled cuts provide flexibility (for example, an ability to stretch) to the composite membrane assembly (such as fiber tape) so that they do not break or crack when being folded to form (or to conform to) a curved shape. Further, the flexibility provided by the angled cuts eliminates, minimizes, or otherwise reduces wrinkles in the composite plies and the composite membrane assembly formed by stacked composite plies.

It has been found that forming a composite membrane assembly from <NUM> or more composite plies as described above provides both strength and flexibility to the formed composite membrane assembly. For example, using only two composite plies may lead to a composite membrane assembly with reduced strength, due to the existence of two separate cuts, each of which spans through <NUM>% of the formed composite membrane assembly. However, by increasing the number of composite plies and staggering the angled cuts, a single contiguous cut through a percentage of thickness of the composite membrane assembly is reduced. For example, if ten composite plies are used to form a composite membrane assembly, a single contiguous cut through any portion of formed composite membrane assembly does not exceed <NUM>% of the thickness of the composite membrane assembly (as cuts of adjacent plies are staggered with respect to one another). If twenty composite plies are used to form a composite membrane assembly, a single contiguous cut through any portion of the formed composite membrane assembly does not exceed <NUM>% of the thickness of the composite membrane assembly, and so on.

As described above, embodiments of the present disclosure provide an improved system and method of forming a composite material that is able to stretch to accommodate curved surfaces without wrinkling, while substantially maintaining strength.

While various spatial and directional terms, such as top, bottom, lower, mid, lateral, horizontal, vertical, front and the like may be used to describe embodiments of the present disclosure, it is understood that such terms are merely used with respect to the orientations shown in the drawings. The orientations may be inverted, rotated, or otherwise changed, such that an upper portion is a lower portion, and vice versa, horizontal becomes vertical, and the like.

Claim 1:
A composite membrane assembly comprising a plurality of composite plies (<NUM>) stacked together, wherein each of the plurality of composite plies (<NUM>) comprises:
a main body (<NUM>) of reinforced fibers (<NUM>) connected together with a resin, wherein the main body (<NUM>) includes a base (<NUM>) connected to an opposed boundary surface (<NUM>) through opposed ends (<NUM>, <NUM>) and opposed sides (<NUM>),
a longitudinal plane (<NUM>) extending between the opposed ends (<NUM>, <NUM>) and being parallel with one or both of the base (<NUM>) and the opposed boundary surface (<NUM>),
wherein a plurality of non-orthogonal cuts (<NUM>) are formed through a thickness of the main body (<NUM>) from the base (<NUM>) to the boundary surface (<NUM>), wherein said plurality of non-orthogonal cuts (<NUM>) form a non-orthogonal angle with respect to the longitudinal plane (<NUM>) of the composite ply (<NUM>); characterized in that
the plurality of non-orthogonal cuts (<NUM>) of one of the composite plies (<NUM>) are opposite from the plurality of non-orthogonal cuts (<NUM>) of an adjacent composite ply (<NUM>).