OF AERODYNAMIC STRUCTURES

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority of U.S. Provisional Patent Appl. No. 63/367,085, filed June 27, 2022, the entire contents of which are incorporated herein by reference.

FIELD OF USE

[0002] The present disclosure is directed to materials having a helicoidal architecture for protecting an aerodynamic profile.

BACKGROUND

[0003] Aerodynamic profiles are highly engineered to provide excellent aerodynamic efficiency. This can only be guaranteed if the shape of the aerodynamic profile does not change over time and if the surface of the profile is maintained as originally manufactured to avoid changes in the air flow around the profile. To this end, erosion of the leading edge (LE) of the aerodynamic profile due to high frequency impacts, and resulting damage of liquid-born and solid-bom particles, such as rain, oil, water, sand, salt, and dust can cause critical losses in aerodynamic efficiency. For aerostructures including drones, commercial, military vehicles, and helicopter rotor blades, this can lead to increased drag with consequent increase in fuel consumption. The change in aerodynamic characteristic of the profile can also introduce a change in the load distribution, which in turn could result in vibrations and, in some cases, also lead to severe structural damage. For rotor blades this can lead to a decrease in power generation for a wide range of applications including wind energy production, jet engine efficiency, power production in submarine propellers as well as stationary gas and water turbines. Similar issues affect aerodynamic profiles of marine applications, including but not limited to fins, master poles, and submarine profiles. [0004] In commercial as well as military aviation, erosion of the aerodynamic surfaces and of the surfaces exposed to the forward-facing flow are heavily subjected to erosion both from liquid and solid borne particles. These include, but are not limited to rain, sand, salt, dust, ash, hail, and ice. The forward facing regions of the aircraft more subjected to erosion and include, but are not limited, to the nose cone, the leading edge (LE) of wing, air intake of the engine, pylon, nacelle, vertical and horizontal stabilizers, and the rotating blades comprising the fan, compressor and turbine blades of an aircraft engine, as well as propeller blades.

[0005] In marine applications, erosion caused by liquid and/or solid-born particles can occur on the hydrodynamic and aerodynamic surfaces of the boat/vessel. These include, but are not limited to, salt, dust, sand, rock debris. Areas such as the forward facing surfaces of a vessel or boat can be damaged by erosion including, but not limited to, propeller blades, mast, wings, rudder, keel, hull, etc.

[0006] The blades of the wind turbine’s rotor are the key components to capture the wind energy and to transform it into electricity. To maximize the annual electricity production (AEP) of a wind turbine, two parameters are important to consider: 1) location where the wind speed will be high and consistent, and 2) capacity and efficiency of the wind turbine design. For these reasons, operators and wind turbine manufacturers have been developing higher capacity turbines with longer rotor blades which results in higher blade speeds, and choosing locations such as offshore regions that demonstrate higher wind environments. As a result, blades are exposed to more extreme conditions and are subjected to more extreme durability challenges during their lifetime: impacts, erosion, delamination, UV exposure, thermal fluctuations, lightning strikes, ice, hailstones, etc. AEP is often significantly impacted by these problems, initially with a reduced aerodynamic efficiency as erosion of the leading edge of the blade begins to occur, followed by maintenance requirements and ultimately, if not repaired, full replacement of the blades or terminated operation of the wind turbine. Recent studies have estimated that blade roughness caused by rain erosion can reduce aerodynamics and ultimately reduce electricity production by 3% to 30% of a wind turbine capacity depending on the severity of the erosion process. Companies still engage in costly inspection and maintenance plans to repair damaged blades during the entire lifetime of a wind turbine as maximizing efficiency of electrical production far out-weighs these costs. [0007] With more knowledge and experience regarding blade dynamics, the industry has been able to increase the length of rotor blades resulting in tip speeds of up to 130-160 meters per second. At these high speeds, critical areas of the blade require improved performance due to extreme deteriorating effects: rain erosion at the leading edge of the blade, impacts with objects on the pressure side (hailstones, birds, bugs, rain, hail, salt, etc.) and high stresses on the blade’s structure. Specifically, during operation, blades will be damaged at different levels of severity, from a surface level which will impact efficiency, to the structural level that can lead to complete failure and premature end of life.

[0008] Therefore, blades require expensive maintenance and repair to ensure the maximum performance and energy output during service operation with additional down-time costs. Thus, monitoring and maintaining the blades to maximize electrical production and ensure a mechanically robust structure is constantly monitored for a cost-benefit analysis. The wind turbine industry has been focused on improving the overall durability of the blade. The area which commands the most focus and attention is the Leading Edge Protection (LEP).

[0009] Current LEP products, including solutions for wind rotor blades and aerostructures have proved unsatisfactory due to challenging applications and disappointing longevity results, including those affected by impact damage caused by rain, sand, dust, hashes, oil, salt, hail, and bird strikes. Rather than relying on an ineffective LEP, most OEMs have adopted a practice of either over-building the minimum wall gauge to improve impact resistance, or to apply metallic shields (especially in aerospace related applications). Both solutions increase the cost of the blades, make the blades heavier, create challenges in delivering a good bonding between dissimilar materials, and create challenges of matching differing materials to have similar flexural characteristics required during operation. Subsequently, for rotating propellers and blades, the added weight to the blades requires more energy to rotate, which also reduces their overall energy efficiency and power production. Further, for fixed aerodynamic surfaces, such as the leading edge of an aircraft wing, the overall weight of the structure is increased leading to overall higher manufacturing costs and increased fuel consumption during operation.

[0010] Most common proposed solutions to increase robustness of the leading edge against erosion rely on the use of metallic shields for aerospace related applications and on the use of polymer-based coatings and paintings such as 3M Wind Blade Protection Coating W4600 and W4601, ReNEW W-Series, HC05XP1 (made available by Hontek, South Windsor, Connecticut), or a RELEST Wind coat (made available by BASF, Ludwigshafen, Germany) for wind energy generation as well as helicopter blade solutions. The thicker the coating, the longer the protection against rain erosion. However, to build up thickness during manufacturing requires several coatings with drying time between. This results in: 1) labor cost increases; 2) weak interfaces are introduced between the layers of coatings leading to loss of protection; 3) the coating often peels off creating flying parts that decreases aerodynamic efficiency as well as increase noise; 4) while the use of such coatings helps with resisting erosion, they are unable to function as a protection against more severe impact damage from hail stones, birds or lightning strikes; and 5) since these coatings are applied manually using brushes or spray techniques, these often lead to variable thickness coated layers with consequent loss of geometrical stability and aerodynamic performance. The last aspect could be obviated with using a protective tape. However, this option presents the same limitations of 1-4 as indicated above.

[0011] Other proposed solutions such as those described in WO 2008/157013 and WO 2013/092211 make use of shield and covers manufactured ahead of being placed on the finished blade. The main disadvantages of such solutions are the following: 1) it is difficult to guarantee the correct geometrical stability of such thin and slender protective covers; 2) it is difficult to handle the small and thin covers during assembly, with the blade shield being very flexible due to the long dimension; 3) they require an additional manufacturing step which requires an additional mold to shape the shell to the complex LE profile; and 4) the increased number of parts increases the manufacturing complexity, cost, and risk of defects due to imperfect integration.

[0012] In addition, WO 2017/198167 describes a proposed solution using a co-curing process where the LEP devised is co-built with the rest of the profile. The proposed solution makes use of one or more layers of short fiber mats or woven fabrics which are impregnated with paint or coating material, while the fiber reinforcement is used to build up thickness and avoid inconsistencies during coating which leads to a more uniform protection. This thicker fabric also assists to reduce crack propagation and protects against more severe damage such as those from hail stone impacts. [0013] Notably, the liquid and solid-born erosion phenomenon has often been treated as a surface problem, but not as a low-energy, high repetition impact problem. The high tip speed reached by the blade (up to 160 m/s) leads to a phenomenon of impact fatigue, with high frequency, low mass (0.015 g), low energy (-0.12 J) impacts repeated on the blade surface. In the case of liquid droplets, the impact of the droplet generates strong water hammer pressure with peaks of -134 MPa, which is close, if not higher than, the strength of standard polymer resins used in FRPs which compose the skin of the blade (commonly made with Glass fiber NCF embedded in a thermoset resin for wind rotor blade applications).

[0014] A better performing solution is to quickly dissipate energy in-plane, rather than through the thickness, to avoid damage localization, and finally have a high dampening coefficient to further dissipate the energy carried by such stress waves. The stress wave propagation can be controlled via changing the impedance of the material being impacted (i.c., LEP) via either changing the constituents composing the material or by changing the architecture of how such constituents are arranged (i.e., the micro structure). In such a scenario of a stress wave dominated problem, reinforcement such as short fiber and woven composites (relevant to WO 2017/198167) are not the optimal choice. The crimp in the woven material as well as the fiber ends in the short fiber composites represent sites of stress concentrations as well as areas subjected to the reflection of the stress waves. This, in turn, results in increased damage formation in the substrate subjected to both rain impact and larger mass impact. Furthermore, the woven and short fiber constructions lead to the formation of several resin reach areas. These act as a site for crack nucleation due to the change in impedance between a fiber reach area and a resin reach area.

[0015] An additional issue related to current LEP solutions is the requirement to use higher- performing materials which unfortunately have a negative environmental footprint, such as glass fiber or high strength metallic shields. In fact, no solution is available that makes use of biobased products both the in terms of polymers as well as reinforcements.

[0016] In view of the foregoing drawbacks of previously known systems and methods, there exists a need for a technology that enables the use of such materials in applications where aerodynamic profiles arc subjected to watcr/sand/dust erosion such as wind blade, aerodynamic surfaces of aerostructures, and rotor blade applications as it would allow for acceptable performance while offering an improved environmental footprint. Sustainable materials such as natural-fiber composites have an estimated 50% lower carbon footprint compared to glass-fiber composites, showing greenhouse gas emission savings of up to 70% compared to their functionally equal fossil-based counterparts.

[0017] It would further be desirable to provide a LEP solution capable of tailoring stress wave propagation speed of the aerodynamic structure and that also provides load carrying strength for the aerodynamic structure.

SUMMARY

[0018] The present disclosure overcomes the drawbacks of previously-known systems and methods by providing a LEP solution that leads to a better rain/sand/dust/water erosion protection exploiting the use of long fiber helicoidal laminates with graded material properties.

[0019] For example, an apparatus for protecting an aerodynamic profile having a length and a leading edge is provided. The apparatus may include a plurality of plies of parallel reinforcing fibers that extends along at least a portion of the length of the aerodynamic profile and over at least the leading edge of the aerodynamic profile, and a resin matrix including a resin permeated between the reinforcing fibers of each ply of the plurality of plies and between adjacent plies of the plurality of plies. Moreover, at least a portion of the plurality of plies may be helicoidally arranged relative to one another to tailor stress wave propagation speed and acoustic impedance of the aerodynamic profile and to provide load carrying strength for the aerodynamic profile and dampen high frequency impacts generated by impact on the aerodynamic profile. For example, the impact may be at least one of rain droplets, hail, dust, ice, sand, or salt.

[0020] The aerodynamic profile may be a wind turbine blade, a fix leading edge of an aircraft, an open rotor blade, a helicopter blade, a nose cone, an air intake of an engine, a pylon, a nacelle, vertical and horizontal stabilizers, a propeller blade, a fan blade, a mast, a keel, a rudder, a wing, or forward facing areas of a boat hull. The parallel reinforcing fibers may include unidirectional long fiber composites and/or a non-crimp fabric. For example, the non-crimp fabric may include a biaxial configuration and/or a quadriaxial configuration, and further may include at least one of e-glass or natural fiber materials. For example, the natural fiber materials may include at least one of flax, sisal, hemp, kenaf, or bamboo. In addition, the parallel reinforcing fibers may include at least one of carbon, glass, aramid, ultra-high-molecular-weight polyethylene (UHMWPE), polypropylene (PP), or a natural fiber.

[0021] The resin may include at least one of a thermoset or a thermoplastic resin. Moreover, a difference in elastic modulus between the resin and the parallel reinforcing fibers may be at least a factor of ten. At least a portion of the plurality of plies may be helicoidally arranged relative to one another in a non-symmetric manner and/or in an unbalanced manner. At least a portion of the plurality of plies extending over the leading edge of the aerodynamic profile may include a pitch angle between 20 and 30 degrees. In addition, at least one of a resin system, fiber reinforcement, or fiber treatment of the apparatus may be selected to tailor the hardness of the aerodynamic profile to thereby tailor stress wave propagation speed and acoustic impedance of the aerodynamic profile.

[0022] Moreover, the plurality of plies may include a first plurality of plies of parallel reinforcing fibers that are not arranged in a helicoidal relationship to provide load carrying strength for the aerodynamic profile, such that an included angle between orientation directions of a first pair of adjacent plies of the first plurality of plies may be 30° or more. Additionally, an included angle between orientation directions of at least one other pair of adjacent plies of the first plurality of plies may be 30° or more. The plurality of plies further may include a second plurality of plies of parallel reinforcing fibers that are arranged in a helicoidal relationship, such that an included angle between orientation directions of at least two adjacent plies may be more than 0° and less than about 30° to provide impact resistance for the reinforced composite structure, e.g., the aerodynamic profile. The apparatus further may include a top coating coupled to the plurality of plies.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG. 1 A illustrates various views of leading edge architectures of a wind energy blade.

[0024] FIG. IB illustrates a composite sandwich structure. [0025] FIG. 1C illustrates a schematic of areas on an aircraft exposed to liquid and/or solid particles impingement that could lead to erosion of an aerodynamic surface.

[0026] FIG. ID illustrates various blades and aerodynamic profiles that may benefit from the reduction of the effect of liquid-bom or solid-born erosion in accordance with the principles of the present disclosure.

[0027] FIG. 2 illustrates an exemplary blade manufacturing process.

[0028] FIG. 3 illustrates an example of a helicoidal geometry.

[0029] FIG. 4 illustrates a stack of fiber layers arranged into a helicoidal pattern in accordance with the principles of the present disclosure.

[0030] FIG. 5A illustrates a helicoidal preform made of straight fiber placement on a 3D curved shape in accordance with the principles of the present disclosure.

[0031] FIG. 5B illustrates a helicoidal preform made of curved fiber placement on a 2D shape in accordance with the principles of the present disclosure.

[0032] FIG. 6 illustrates a helicoidal laminate stack.

[0033] FIG. 7A illustrates uni-directional material form, and FIG. 7B illustrates non-crimped multi-axial material form.

[0034] FIG. 8 illustrates results of rain erosion tests (ASTM G76) performed on two aerodynamic profiles representative of a leading edge in a wind rotor blades.

[0035] FIG. 9 illustrates a schematic of possible construction of the leading edge protection with a fiber reinforced construction at least partially helicoidally arranged in accordance with the principles of the present disclosure.

[0036] FIGS. 10A to 10C are schematic views of a structure that includes both impact resistance and load carrying strength. [0037] FIG. 11 is a flow chart illustrating exemplary method steps for forming an aerodynamic blade having a helicoidal architecture in accordance with the principles of the present disclosure.

DETAILED DESCRIPTION

[0038] The present disclosure overcomes the drawbacks of previously-known systems and methods by providing a LEP solution for a generic aerodynamic profile that leads to a better erosion and impact protection exploiting the use of long fiber helicoidal laminates with graded material properties. FIG. 1A illustrates the LE architectures adopted in wind energy blades, e.g., a wind turbine blade. As shown in the FIG. 1A, wind turbine blade 100 may include leading edge (LE), trailing edge (TE), spar cap (SC), and shear webs (SW). The construction of leading edge (LE) may include a monolithic composite. For example, the leading edge construction may include 500-1000 pm filler (putty), sandwiched between 2-3 layers of 500-1000 pm LEP coating and 2 biaxial layers of 0.8-1.6 mm fiberglass (epoxy). Moreover, leading edge (LE) of wind turbine blade 100 may include a bonded joint. In addition, the shell construction of wind turbine blade 100 may include a sandwich composite formed by foam core (FC) sandwiched between adjacent layers of FRP face sheet.

[0039] For example, placing a material including, e.g., a polymer layer on foam material between composite laminate face sheets, as shown in FIG. IB, creates a synergistic structural configuration in which the face sheets provide bending stiffness and the sandwich material provide shear rigidity and buckling resistance. Compared to monolithic laminate composites, sandwich panels may exhibit improved strength-to-weight ratios, sound deadening, fatigue capability, thermal insulation, and impact/damage resistance. Sandwich panel impact performance may be superior to laminates since some of the energy associated with a strike may dissipate as elastic deformation instead of matrix and/or fiber damage and/or the core may cushion inertial loads while the face sheet performs the energy absorption. However, while the laminate composite may deform, the coatings often used in these applications do not have the same flexural characteristics which may result in the coating to crack which will materially reduce their performance and result in premature end of life. Laminate face sheet configuration, core typc/structural properties, and boundary conditions control the impact behavior. Typically, in sandwich designs the face sheets are relatively thin and the core is bonded to the face sheets with an adhesive. Structural and failure mechanisms that make sandwich inappropriate for some applications include the following: a) because of limited bond area and strength the face sheets may prematurely separate from the core during impact; b) since the face sheets are thin relative to an equivalent laminate design fiber breakage, fiber matrix de-bonding and laminate delamination can initiate at lower impact levels; c) the core can crush or experience shear deformation; and d) replacing laminate plies with sandwich material can degrade in-plane structural properties like compression, tension, strength and stiffness.

[0040] FIG. 1C illustrates areas of an aircraft structure that may be improved with the invention disclosed herein. FIG. ID illustrates other types of blades and aerodynamic profiles constructions found in other industrial applications that would benefit from the disclosed invention as to reduce the effect of liquid-born or solid-born erosion. These include, but arc not limited to, propeller blade, wing leading edge, air engine intake, engine nacelle, nose cone, helicopter blades, compressor/turbine blades, and open rotor propellers for aero and marine applications.

[0041] The solutions described herein are based on the use of long (>2mm) fiber reinforced composites having a helicoidal architecture, such as those described in U.S. 2021/0316528 and U.S. 2021/0339499, both assigned to assignee of the instant application, the entire contents of each of which are incorporated herein by reference, with material aligned with a graded hardness and stiffness to develop an efficient and highly tailorable LEP solution with longer durability than conventional solutions while yielding lighter, and optionally, more environmentally sustainable solutions.

[0042] Referring now to FIGS. 2A to 2D, an example of the blade manufacturing process is described for wind rotor blades. The long fiber reinforced composites having a helicoidal architecture may be applied to the wind turbine blade during material preparation of the fiber, core, etc. of the wind turbine blade, as shown in FIG. 2A. The use of such high-impact resistant fiber reinforcement LEP holds the potential to reduce the amount of coating needed to protect against rain erosion, protect against more catastrophic events such as bird or lightning strikes, and further reduce the structural weight of the blade and which can also lead to longer blades with higher energy production. As described in further detail below, resin infusion may be conducted on the suction side and the pressure side of the wind turbine blade, as shown in FIG. 2B. Moreover, each shell and the shear webs of the wind turbine blade may be assembled, e.g., via adhesive, as shown in FIG. 2C, and the wind turbine blade may be demolded, trimmed, and polished, as shown in FIG. 2D.

[0043] Contrary to past proposed solutions, which has made use of woven long fiber composites, the present disclosure uses graded long fiber composites having a helicoidal architecture, such as the helicoidal geometry shown in FIG. 3. As used herein, the term “helicoidal” refers to a stacking arrangement of plies of fibers, as shown in FIG. 4, wherein the fibers of at least one ply define an orientation direction relative to an orientation direction of the fibers of an adjacent ply and that provide an included angle greater than 0 degrees and less than about 30 degrees. The stacking arrangement may include adjacent plies that define included angles outside of this range, and the stacking arrangement may have less than a full rotation of 360 degrees, or may have more than one full rotation. The fiber orientation direction of one or more plies may be straight or curved. For example, FIG. 5A illustrates a helicoidal preform made of straight fiber placement on a 3D curved shape, and FIG. 5B illustrates a helicoidal preform made of curved fiber placement on a 2D shape.

[0044] For example, FIG. 6 illustrates a fiber reinforced elastic composite ply stacking approach in which the individual layers are rotated along the longitudinal or x-direction axis at a predefined angle relative to the adjacent layers so as to create a z-direction helicoidal fiber- oriented stack. The left-hand image uses a single line to represent each ply layer (lamina), this view highlights the generated z direction helicoidal spiral. The right-hand image uses fiber bundles (tows typically consisting of 3,000 to 50,000 fibers or more) to more realistically show the construction layers of a helicoidal layup. The subsequent blow ups show how the helicoidal laminate stack is formed of individual laminae layers that are formed of fiber tow and resin. Helicoidal clocking may be chosen to create a specific spiraling pitch or circular polarization z orientation fibers that are in close enough proximity as to exhibit significant interlaminar-like direct load sharing between laminate fibers. [0045] The ability of the fibers to load share directly between laminae plies is a significant contributor to a helicoidal laminate’s ability to absorb and dissipate impact forces more efficiently than conventional composite layups and minimize the effects of impact fatigue. Further, the spiral formed from the assembly of these pitched fibers may be tuned to a specific wavelength to dampen propagating shock waves initiated by impact forces on the aerodynamic profile, and further may be filled with a matrix that contains microspheres or toughening particles to further prevent or arrest propagation of catastrophic fractures and may be made to exploit the difference in elastic moduli between the fibers and resin to further arrest fractures generated from blunt or sharp impacts.

[0046] Moreover, the graded long fiber composites may be in the form of uni-directional (UD) and/or Non-Crimp Fabrics (NCF), which will allow for: 1) the fibers to remain straight and avoid areas where the stress waves generated during the erosion process could be arrested and reflected generating damage (such as in the crimp region of woven fabrics or at the end of short fibers); 2) a more uniform in-plane stress wave dispersion to allow for a quick dispersion of stress waves; and 3) a tailored through-the-thickness stress wave dispersion for optimal dampening in the 3D space. For example, FIG. 7 A illustrates UD manufacturing, and FIG. 7B illustrates an example of non-crimped multi-axial fabric. Overall, the combined action of these features will allow the material to: 1) relax quickly before subsequent impact events; 2) better dampen the high frequency impacts generated by repeated water droplets, sand, or salt; and 3) better diffuse energy in-plane, which results in less localized damage.

[0047] The fiber architecture of the layup shall contain, at least partially, a helicoidal layup. In the context of wind rotor blades, the use of ASTM G76 tests have demonstrated, as shown in FIG. 8, that the helicoidal layup described herein compared to conventional layups used in wind blade applications is capable of greatly reducing the eroded mass by about 34%. This is achieved due to the ability of the helicoidal fiber arrangement to better dampen stress waves, dissipating them away from the impact location, as well as spreading damage in plane by forming sub-critical matrix damage that allows for the impact energy to be dissipated while preserving structural integrity. FIG. 8 illustrates one profile utilizing NCF fibers in a conventional architecture used in-field applications and an aerodynamic profile characterized by NCF fibers hclicoidally arranged. [0048] FIG. 9 illustrates a schematic of possible construction of the leading edge protection with a fiber reinforced construction at least partially helicoidally arranged, potentially, in combination with other material components to tailor the stress wave propagation characteristic of the multi-material solution, aiming at improving erosion and impact resistance.

[0049] In some embodiments, the helicoidal layup may be non-symmetric and/or unbalanced. For example, as the region of the LEP has high curvature, and is limited to a small region of a much larger structure, the effect of stiffness coupling may not be relevant. Further, the pitch angle may be kept constant or be variable to provide tailored performances. This is to promote certain types of damage within the composite such as delamination between the helicoidal layers, which will further help to dissipate energy and reduce damage. For example, the use of a larger pitch angles (between 20° and 30°) at the side of the LEP closer to the blade surface will allow to arrest eventual cracks that originally form on the top or exterior surface of the blade.

[0050] As described above, the graded long fiber composites having a helicoidal architecture, e.g., a helicoidal stack, may be made using NCF. As long fiber NCF are the typical fabric used for the manufacturing of the wind blade skins as well as wing skins of aircrafts, this will make the manufacturing and handling of the LEP easier. NCF could be biaxial (BX) such as X°/-X° layers slightly rotated to create the helicoidal layup or by developing a multiaxial (MX) fabric with layup X°/X ⁰ +a/X ⁰ +2a/X ⁰ +3a/.../ X°+n*a where a represents the inter-ply angle between adjacent plies to form the helicoidal layup and n+1 represents the total number of plies composing the MX fabric. The inherent design of a MX already embeds a partial helicoid. With this it would be possible to create the LEP by using only a few layers of material during the layup with minimum waste and reducing labor costs and complexity of manufacturing.

[0051] Suitable fibers that may be used for the LEP may include, for example, carbon, glass, aramid, ultra-high-molecular-weight polyethylene (UHMWPE), polypropylene (PP), and various natural fibers. Moreover, suitable resin systems may include thermoset, thermoplastic, vitrimer and self-healing polymer resins formed with either synthetic or natural polymer precursors. In order to promote the activation of failure mechanisms including sub-critical damage formation and spiraling cracks, the difference in clastic modulus between resin and fiber should at least be a factor of ten. This will grant the activation of crack deflection mechanisms, paramount to diffuse damage helicoidally.

[0052] In some embodiments, the helicoidal stack may be made with NCF reinforcement made of E-Glass, which is a typical material used to make the blade skins in the wind rotor market, or of natural fiber materials, e.g. flax, sisal, hemp, kenaf, bamboo, etc., which are characterized by outstanding dampening properties. As glass fiber is higher performing and less subject to environmental effect, e.g. moisture absorption, it would be very challenging at equal or better performance to replace the blade completely with natural fibers. However, since the LEP covers only a small portion of the blade surface, this represents a cost-effective solution to introduce a more sustainable material within the wind blade market. Further, an LEP that is replaced during maintenance will generate less waste and have a higher grade of recyclable and bio-based materials, thereby decreasing the environmental footprint of the proposed solution.

[0053] In another embodiment, the helicoidal stack may be made using carbon fiber UD prepreg stack of NCF. This would be more relevant to aerostructures which make a more extensive use of carbon fiber materials.

[0054] The graded hardness of helicoidal LEP protection may be achieved by hybridizing the type of fiber used within the helicoidal layup. For example, the use of flax hybridized with glass fiber when in helicoidal form provides superior impact resistance versus that of a conventional glass-only solution. Moreover, a hybrid NCF helicoidal LEP using glass fiber/epoxy material at the most external layer of the LEP (only a few layers) may provide the appropriate hardness for quick stress wave propagation supported by a high damping material, such as flax-epoxy composite. In this way: 1) the graded hardness would allow for faster dissipation of stress waves at the impact point; and 2) part of the glass material, which has poor recyclability and is heavy, may be replaced with flax material, which is a better environmental solution and lighter material that also provides damping. All of the aforementioned layers would be at least partially arranged in a helicoidal layup, as described herein. In another embodiment, layers of different fiber types may be dispersed within the laminate thickness rather than blocked together in specific regions of the laminate. [0055] The helicoidal reinforcement further may be built using materials with a progressively increasing hardness by changing the material constituents, not the fiber architecture/layup. This may allow for a quicker dispersion of stress waves as, for example, a rain droplet impacts the surface and hence would result in a delayed crack initiation at the surface. For example, such graded materials may be achieved using either: 1) different resin systems (e.g., wet layup procedure during placement of each layer of the LEP, before curing or post-curing treatment, or varied resin to catalyst mixtures, to increase hardness, or by adding an additional phase to the matrix); or 2) different fiber reinforcements and/or fiber treatment. Having harder fibers may help to increase the stress waves propagation speed depending on the new ratio of longitudinal and bulk moduli over the new density of the harder fiber. This may be beneficial to help the material relax during the high frequency impacts of, e.g., rain droplets. Another example of graded helicoidal material may be achieved by targeting a difference in density between the helicoidal layers. For example, this may be achieved by using NCF or UD fabrics with same fiber areal weight but different yam sizes. For the same grams per square meter (gsm), using low fiber count yams leads to a more uniform distribution of fibers, while a higher fiber count yarn leads to a more “inconsistent” fabric. Thus, for the same fiber areal weight of the fabric, the density distribution in each ply is more uniform in a 68 tex while with periodic changes in a 200 tex.

[0056] In some embodiments, the graded hardness helicoidal protection may be realized with a step change in hardness properties between the helicoidal composite substrate and a top coating. For example, this may be achieved by spreading a coating on the surface of the helicoidal composite substrate to generate two distinct regions characterized by uniform homogenized hardness.

[0057] The helicoidal material described herein may be used to form the aerodynamic profile to prevent cracks from propagating along the underneath stmeture. For example, FIGS. 10A to 10C show schematic views of a ply arrangement for a fiber-reinforced composite stmeture 1000 according to embodiments of the present disclosure. FIG. 10B represents a cross section of the stmeture shown in perspective in FIGS. 10A and 10C. Composite stmeture 1000 may have first plurality of plies 1002 of reinforcing fibers defining a first region of the fiber reinforced composite structure, the plies having parallel fibers, and wherein the plies arc arranged to provide load-carrying strength for the reinforced composite structure. In the example shown, first plurality of plies 1002 includes five plies. The two plies at the bottom are arranged at +80 degrees/-80 degrees, and the three plies above those are both arranged at 0 degrees. In this example, the 0 degrees plies are arranged along the axis of an axisymmetric part, such as a tubular structure, and provide strength in the direction of primary loading. The +80 degrees/-80 degrees plies serve to reinforce the 0 degrees plies and resist buckling of the axisymmetric part, such as might be advantageous in long, thin tubular structures.

[0058] Second plurality of plies of reinforcing fibers 1004 define a second region of the fiber reinforced composite structure and are arranged in a helicoidal relationship, wherein an included angle between the orientation directions of at least two adjacent plies is more than 0 degrees and less than about 30 degrees to provide impact resistance for the reinforced composite structure. In the illustrated example, the plies (starting from the top and working down) arc arranged at 70 degrees, 65 degrees, 60 degrees, 55 degrees, 50 degrees, 45 degrees, 40 degrees, 30 degrees, 20 degrees, and 10 degrees. As described herein, this helicoidal relationship provides impact resistance to the underlying structure. Although shown with thin ply uni-directional (TPUD) plies for the second plurality of helicoidal plies and thick plies for the other plies, which provides advantages in terms of impact resistance, primary load carrying ability and reduced layup time, the thickness of the plies may be the same for each of the plies.

[0059] Referring now to FIG. 11, exemplary method 1100 for forming an aerodynamic profile with reinforcing fiber composites having a helicoidal architecture is provided. Method 1100 may be implemented in a generic cost-effective way using manufacturing technologies and methods currently used which may be easily integrated in the manufacturing process of the aerodynamic structure to reduce complexity and to ease maintenance operations. At step 1102, a patch of a plurality of plies of parallel reinforcing fibers may be applied along at least a portion of a length of the aerodynamic profile and over at least the LE of the aerodynamic profile, such that at least a portion of the plurality of plies are helicoidally arranged relative to one another to tailor stress wave propagation speed and acoustic impedance of the aerodynamic profile and to provide load carrying strength for the aerodynamic profile. At step 1104, the aerodynamic profile may be co-infused with a resin between the reinforcing fibers of each ply of the plurality of plies and between adjacent plies of the plurality of plies to form a resin matrix. Each shell and the shear webs of the aerodynamic profile may then be assembled, e.g., via adhesive. The aerodynamic profile may then be demolded, trimmed, and polished. Alternatively, the patch of helicoidal graded material may be applied directly to the already manufactured aerodynamic profile for quick replacement and maintenance. This will also allow protection of aerodynamic profiles which are currently in operation and extend their durability and productivity.

[0060] While various illustrative embodiments of the invention are described above, it will be apparent to one skilled in the art that various changes and modifications may be made therein without departing from the invention. The appended claims are intended to cover all such changes and modifications that fall within the true scope of the invention.