Layered carbon fiber composite multi-rotor unmanned aerial vehicle blade and preparation method thereof

Abstract

This invention relates to the field of UAV propeller technology, and discloses a layered carbon fiber composite multi-rotor UAV propeller and its preparation method. The propeller adopts a functionally graded layered composite structure, consisting of, from the inside out, a core load-bearing layer, an internally built-in high-toughness crack-arresting layer symmetrically arranged on the upper and lower sides of the core load-bearing layer, and a surface damping layer symmetrically arranged on the outside of the internally built-in high-toughness crack-arresting layer. The leading edge region of the surface damping layer has a nano-alumina wear-resistant reinforcement layer, and the entire propeller has a mirror-symmetrical structure along its thickness center. During preparation, a semi-cured wear-resistant reinforcement layer is first prepared on the leading edge of the upper and lower molds, and then the surface damping layer, crack-arresting layer, and core load-bearing layer are sequentially laid and mirror-symmetrically stacked. The propeller is then obtained through mold closing, vacuuming, stepped temperature-controlled pressure co-curing, and slow cooling. The propeller of this invention combines high load-bearing capacity, high toughness, excellent erosion resistance, and damping vibration reduction performance, significantly improving flight safety redundancy and service life.

Description

Technical Field

[0001] This invention relates to the field of unmanned aerial vehicle (UAV) propeller technology, specifically to a layered carbon fiber composite multi-rotor UAV propeller and its preparation method. Background Technology

[0002] As multi-rotor drones rapidly develop towards higher payload, longer endurance, and higher maneuverability, drone propellers must simultaneously meet comprehensive performance requirements such as structural strength, lightweighting, impact resistance, and weather resistance. Currently, high-performance drone propellers are mostly made of pure carbon fiber composite materials, typically combining carbon fiber fabric with epoxy resin. The carbon fiber prepreg is layered in a mold and then cured under high temperature and pressure. This process can achieve lightweighting while ensuring the basic strength of the propeller blade, and has become the mainstream manufacturing method for drone propellers. However, this traditional technology only focuses on meeting the single performance requirements of strength and lightweighting, without considering the multi-dimensional performance requirements of impact resistance, erosion resistance, vibration reduction, and noise reduction in actual drone service scenarios. The composite material system has inherent defects and is difficult to adapt to the complex operating conditions of drones.

[0003] While pure carbon fiber / epoxy resin composite blades offer advantages in lightweight design and structural rigidity, their homogeneous material system and simplistic high-temperature hot-pressing process result in significant shortcomings in key performance areas such as impact resistance, wind and sand erosion resistance, vibration reduction, and fatigue resistance. Firstly, the blade material is highly hard and brittle, lacking a tough, energy-absorbing phase and crack-blocking structure. Under sudden impacts such as bird strikes or foreign object collisions, stress concentration cannot be quickly relieved, and microcracks can easily penetrate the cross-section, leading to brittle fracture. Without the safety redundancy of "fracture without separation," this greatly increases the risk of drone crashes. Secondly, the high leading-edge velocity of the blades during high-speed rotation, combined with the low hardness of conventional epoxy resin matrices and thin surface protective layers, makes them susceptible to high-speed particle impacts in windy and sandy environments. Corrosion leads to resin wear and peeling, and exposed carbon fiber with fuzzing, which disrupts the airfoil aerodynamic profile and blade dynamic balance, reducing aerodynamic efficiency and shortening service life. Third, pure carbon fiber / epoxy resin materials have poor damping performance and weak ability to attenuate motor and aerodynamic vibrations, which can easily cause structural resonance and generate sharp noise. At the same time, alternating stress tends to accumulate at the blade root, inducing microcrack propagation and leading to early fatigue failure of the blade. Fourth, the traditional single high-temperature rapid hot pressing process is only suitable for molding homogeneous carbon fiber prepregs and cannot be compatible with composites of heterogeneous materials such as tough fibers and thermoplastic resins. This can easily lead to problems such as poor interface bonding, many interlayer pores, and thermal damage to the tough fiber structure, making it difficult to achieve synergistic performance of multiple materials and restricting the improvement of the overall blade performance. Summary of the Invention

[0004] The purpose of this invention is to provide a multi-rotor drone blade made of layered carbon fiber composite material. This blade has high load-bearing capacity, high toughness, high erosion resistance and high damping vibration reduction performance, which can improve flight safety redundancy and service life.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A multi-rotor drone blade made of layered carbon fiber composite material adopts a functionally graded layered composite structure, consisting of a core load-bearing layer, an internal high-toughness crack arresting layer symmetrically arranged on the upper and lower sides of the core load-bearing layer, and a surface damping layer symmetrically arranged on the outside of the internal high-toughness crack arresting layer from the inside out; the blade leading edge region of the surface damping layer is provided with a nano-alumina wear-resistant reinforcing layer, and the blade as a whole has a mirror symmetrical structure along the center of thickness.

[0006] The core load-bearing layer acts as the "backbone" of the propeller. Its extremely high axial tensile strength and bending stiffness can resist the huge centrifugal force and aerodynamic bending moment generated by the propeller at high speed (such as thousands of RPM), ensuring that the complex shape of the blade does not twist or deform, thereby maintaining the set aerodynamic noise reduction efficiency; the surface damping layer is located on the outermost windward and leeward sides of the blade.

[0007] Preferably, the core load-bearing layer is a composite of high-strength carbon fiber unidirectional tape and toughened modified epoxy resin, using high-strength carbon fiber unidirectional tape (UD) as the reinforcement and toughened modified epoxy resin as the matrix. Symmetrical multi-angle (e.g., 0° / ±45°) cross-layouts are designed using computer-aided design, employing high-strength carbon fiber unidirectional tape to achieve 100% material mechanical property conversion rate. The addition of toughened modified epoxy resin enhances interlayer bonding. The built-in high-toughness crack-arresting layer is a composite of ultra-high molecular weight polyethylene fiber fabric and the same resin system. Using ultra-high molecular weight polyethylene (UHMWPE) fiber fabric as reinforcement and toughened modified epoxy resin as matrix, this patent ensures interfacial compatibility and interlayer bonding with the core layer. Existing technologies lack crack-arresting structures; this patent innovatively incorporates a high-toughness UHMWPE fiber layer to replace the traditional brittle carbon fiber layer as a crack barrier. The built-in high-toughness crack-arresting layer utilizes the extremely high elongation at break, cut resistance, and energy absorption properties of UHMWPE fibers. When a violent external impact (such as a bird strike or aircraft crash) causes brittle fracture of the outer carbon fiber layer, the crack, once it propagates... At this layer, the UHMWPE fiber mesh absorbs a large amount of fracture surface energy through tensile deformation, blunting the crack tip and forcibly preventing crack penetration, causing the blade to exhibit a "tearing and fraying" state rather than "instant breakage," thus buying valuable emergency landing time for the drone. The surface damping layer is a PA12 composite material doped with short-cut carbon fibers. Using nylon (PA12) composite short-cut carbon fibers as the matrix, nano-sized alumina wear-resistant particles are concentrated and injected into the windward region of the blade's leading edge, achieving localized and precise reinforcement of the leading edge with nano-alumina. Compared to nylon... Epoxy resin has excellent viscoelasticity, which, combined with the micro-displacement of chopped carbon fiber, forms a highly efficient vibration damping layer. It can effectively absorb and dissipate the high-frequency mechanical vibration transmitted by the motor and the energy of airflow pulsation on the blade surface, and suppress structural resonance fatigue. The high-density nano-alumina particles at the leading edge form "micro-diamond armor", which greatly improves the surface hardness. When cutting through air mixed with sand and ice crystals at high speed, it can effectively resist the impact and wear of hard particles, solve the problems of easy fuzzing of carbon fiber and easy peeling of resin, and ensure the long-term integrity of the aerodynamic profile at the leading edge.

[0008] Specifically, the core load-bearing layer, as the main load-bearing component, is made of high-strength carbon fiber unidirectional tape and toughened modified epoxy resin composite. The volume fraction of carbon fiber is controlled at 55%-65% (corresponding to a mass fraction of 70%-80%), and the volume fraction of resin is 35%-45% (mass fraction of 20%-30%), thus balancing high strength, high modulus, and resin's wettability on the fiber. The built-in high-toughness crack-arresting layer uses ultra-high molecular weight polyethylene fiber fabric and the same resin system. The volume fraction of fiber fabric is set at 50%-60% (mass fraction of 60%-70%), and the volume fraction of resin is 40%-50% (mass fraction of 20%-30%). The rigid fiber content is 30%-40%, ensuring the integrity of the fabric structure while achieving the toughness required to resist crack propagation through full resin impregnation. The surface damping layer is a PA12 composite material doped with short-cut carbon fibers, with a volume fraction of only 5%-15% (mass fraction of 4%-12%) of short-cut carbon fibers and the remaining 85%-95% being PA12 matrix (mass fraction of 88%-96%). Vibration energy is dissipated through interfacial friction between the low-content rigid fiber and the flexible matrix, while maintaining the damping foundation and processing fluidity of the matrix. The overall proportion system has been verified by engineering design and can achieve optimal matching between load-bearing, crack arrest and damping functions.

[0009] Setting the material proportions of the three functional layers to different ranges is based on an engineering balance of the main functional requirements and material properties of each layer. In the main load-bearing layer, the carbon fiber volume fraction is set at 55%-65%. This is to maximize the load-bearing efficiency of the fibers while ensuring sufficient resin impregnation, as carbon fiber is the primary stress-bearing phase. A resin content of 35%-45% is sufficient to ensure the matrix's encapsulation of the fibers and the transfer of interfacial stress. In the built-in crack-arresting layer, the fiber fabric volume fraction is 50%-60%, and the resin content is 40%-50%. This is to maintain the stability of the fabric structure while allowing the resin to play a bridging and toughening role during crack propagation, dissipating energy through plastic deformation and fiber pull-out. In the surface damping layer, the chopped carbon fiber volume fraction is only 5%-15%, while the PA12 matrix is ​​as high as 85%-95%. This is because the damping function mainly relies on matrix deformation and frictional energy dissipation at the fiber-matrix interface. Excessive fiber content would reduce the material's flexibility and damping efficiency. At the same time, the high proportion of PA12 also ensures good processing fluidity for this layer. This layered and differentiated mix design is intended to simultaneously meet the comprehensive performance requirements of high strength load-bearing capacity, crack propagation resistance, and vibration and noise reduction in the overall structure.

[0010] Preferably, the thickness proportions of each layer in the blade structure strictly adhere to the principle of matching structural functional requirements with material mechanical properties. Specifically, the core load-bearing layer occupies a dominant proportion of 50% of the total thickness. The fundamental reason for this is that this layer needs to bear the main mechanical loads during blade operation, including centrifugal force, aerodynamic force, and inertial force. According to the beam theory of material mechanics, sufficient cross-sectional thickness is the basis for ensuring section modulus and moment of inertia. This proportion can effectively control the structural self-weight while meeting the strength and stiffness design requirements, avoiding an increase in rotational inertia due to excessive cross-section. The built-in high-toughness crack arresting layer is set at 10%, which is based on the optimization results of fracture mechanics. This proportion aims to ensure that the material has a sufficient volume fraction to generate significant crack propagation resistance, i.e., high fracture toughness KIC, thereby effectively inhibiting the initiation and propagation of fatigue cracks, while preventing structural imbalance caused by excessive thickness of this layer (material density is usually high). The 15% thickness of the surface damping layer is to maximize the energy dissipation mechanism of the viscoelastic material. According to the principle of damping structure dynamics, this thickness can ensure sufficient interlaminar shear strain under alternating loads, thereby converting more mechanical energy into heat energy for dissipation, so as to achieve the purpose of vibration reduction and noise reduction. Moreover, this proportion is at the optimal balance point between damping efficiency and added mass.

[0011] Another objective of this invention is to provide a method for preparing multi-rotor drone blades made of layered carbon fiber composite materials, thereby achieving integrated co-curing molding of heterogeneous materials and improving the blades' impact resistance, erosion resistance, vibration reduction, and fatigue resistance.

[0012] To achieve another objective of this invention, the following technical solution is adopted: A method for preparing multi-rotor drone blades made of layered carbon fiber composite material includes the following steps: Step 1: Pre-treat the lower and upper mold cavities respectively. Prepare wear-resistant reinforcing layers in the leading edge regions of the blades corresponding to the lower and upper molds, and bake the epoxy resin to a semi-cured state. This means that the resin system is in the intermediate stage (B-stage) of transition from a flowable liquid (A-stage) to a completely insoluble and infusible solid (C-stage). In this state, the resin molecular chains have partially cross-linked. Although it has lost its initial fluidity, it still maintains a certain degree of viscoelasticity and micro-viscosity. It can maintain its shape at room temperature to prevent flow and collapse. At the same time, it can further soften and flow when heated and eventually fully cure. This ensures that the wear-resistant reinforcing layer does not shift during the subsequent complex layup and pressurization processes and can form a good interfacial interlock and bond with the matrix. Typically, it should soften and have a certain fluidity when heated, but not revert to a completely liquid after cooling, nor become brittle and hard like a fully cured material. This enhances the toughness of the material and completes the leading edge reinforcement of the lower and upper molds. Step 2: Lay the lower surface damping layer inside the lower mold cavity where the leading edge has been reinforced; Step 3: Lay the underlying high-toughness crack arresting layer on the lower surface damping layer; Step 4: Lay the core load-bearing layer on the lower built-in high-toughness crack arrest layer; Step 5: Based on the core load-bearing layer, and following the principle of mirror symmetry, lay the upper built-in high-toughness crack arresting layer and the upper surface damping layer in sequence; the mirror lay-up and multi-phase material balancing design establish a neutral axisymmetric balance between the physical force properties and thermal strain characteristics of the cross section, eliminate the mismatch of thermal expansion coefficients of heterogeneous materials and the uneven warping deformation caused by residual thermal stress after curing, and ensure the geometric dimensional accuracy after curing. Step 6: Close the upper and lower molds and evacuate them. Use stepped temperature control and pressure to perform integrated co-curing. After slow cooling and shaping, demold to obtain the multi-rotor drone blades made of layered carbon fiber composite material.

[0013] This preparation method solves the problems of poor interfacial bonding of heterogeneous materials, mismatch of thermal expansion coefficients, and high-temperature failure of tough fibers, and achieves synergistic performance of carbon fiber, UHMWPE fiber, PA12, and nano-alumina.

[0014] During the pretreatment of the lower and upper mold cavities, the cavities are cleaned and coated with a high-temperature resistant semi-permanent release agent (baked at 60-80℃ for cross-linking). Solvent-resistant polyimide tape is used to precisely mask the non-leading edge areas. Using a precision CNC spraying device with micro-nozzles, the wear-resistant reinforcing layer slurry is sprayed onto the narrow area corresponding to the leading edge. The thickness is strictly controlled between 0.1-0.2mm through a multi-pass cross-coating process. After spraying, the tape is removed, and the mold is pre-baked in an environment of 80-100℃ for 20-40 minutes to allow the resin to develop initial adhesion and be in a semi-cured state, preventing the reinforcing layer from being washed away and displaced during subsequent lay-up operations and high-pressure liquid resin flow. By concentrating nano-alumina particles in the leading edge region of the blade, a locally high-hardness erosion-resistant protective layer is constructed. This layer can resist the erosion and wear of airflow carrying hard particles such as sand and ice crystals during high-speed rotation, suppress carbon fiber fuzzing and resin peeling, and maintain the geometric integrity and aerodynamic performance of the leading edge aerodynamic profile.

[0015] The treatment of the wear-resistant reinforcement layer into a "semi-cured state" (B-stage) is determined by the uniqueness of the heterogeneous material co-curing process in this patent and the quality requirements of the interface bonding. If subsequent layers are laid directly after spraying the nano-alumina wear-resistant slurry, the resin is in a completely liquid state (A-stage). On the vertical or inclined mold cavity wall, under the action of gravity and the subsequent high-pressure resin flow, it is very easy to flow, accumulate, or have missing edges. The semi-cured state gives the resin a certain yield strength and shape retention ability, which allows it to adhere firmly to the predetermined area, ensuring that the leading edge coating thickness is uniform and the outline is clear. Meanwhile, the semi-cured state means that the resin molecular chains have undergone partial cross-linking. Although it has lost macroscopic fluidity, it still retains viscoelasticity and micro-viscosity at the microscopic level. When the surface damping layer (PA12) is subsequently laid and pressurized at 120-130℃, this micro-viscosity semi-cured layer can undergo molecular-level interdiffusion and entanglement with the upper material to form a mechanically interlocked structure. This solves the industry problem of poor interfacial compatibility and easy delamination between carbon fiber / epoxy resin and PA12 thermoplastic material. In addition, this is also a necessary means to balance process window and safety. If it is directly baked to full curing (C-stage), the resin will become hard and brittle, which will not only fail to form an effective chemical bond with the subsequently laid material, but will also generate micro-cracks under pressure. The semi-cured state leaves reaction space for the final "stepped temperature control pressurization", allowing the wear-resistant layer to complete densification simultaneously with other layers under the final high pressure and high temperature environment, ensuring that the blade leading edge becomes a solid integral piece, rather than an easily detachable patch glued on later.

[0016] The surface damping layer is a PA12 prepreg tape doped with short-cut carbon fibers. Utilizing the viscoelastic characteristics of the PA12 matrix and the microscopic interface slip dissipation mechanism of the short-cut carbon fibers during stress, a highly efficient vibration damping layer is constructed. The thickness on one side is strictly controlled at 0.62 mm to ensure that the total crack arresting layer thickness accounts for 20%. A special metal roller is used to flatten the layer under high pressure in one direction, completely squeezing out the air bubbles trapped between the layers to ensure a tight bond between the layers. This layer can absorb and dissipate the high-frequency mechanical vibration transmitted by the motor and the airflow pulsation energy on the blade surface, reduce the structural resonance amplitude, and improve fatigue life.

[0017] By uniformly bonding and laying UHMWPE two-dimensional woven fabric pre-impregnated with toughened epoxy resin, a built-in high-toughness crack-arresting layer is formed. The thickness of this layer on one side is strictly controlled to be 10% of the total thickness (e.g., 0.62mm for a total thickness of 6.2mm). During laying, a special metal roller must be used to flatten it under high pressure in one direction to completely squeeze out the tiny air bubbles trapped between the layers. When the blade is subjected to strong external impact (such as bird strikes) that causes cracks to initiate in the outer brittle carbon fiber, the UHMWPE fiber mesh, with its extremely high elongation at break, cut resistance, and high specific energy absorption characteristics, absorbs a large amount of surface energy of crack propagation through the tensile deformation and bridging effect of the fibers, blunts the crack tip, and prevents the crack from penetrating and propagating. This allows the blade to exhibit progressive toughness failure characteristics under extreme loads, avoiding catastrophic brittle fracture, thereby improving the structural safety redundancy of the UAV under extreme conditions.

[0018] When the upper and lower molds are closed and vacuumed, after the upper and lower molds are precisely locked, they are immediately installed into the vacuum system and vacuumed to the ultimate negative pressure of -0.098MPa. The negative pressure effect is used to extract all the macroscopic air and low molecular volatiles remaining between the layers.

[0019] After cooling, the mold is opened to obtain layered carbon fiber composite drone propellers that are bubble-free, warp-free, and have synergistic performance.

[0020] Preferably, the wear-resistant reinforcing layer is made by dispersing nano-alumina particles in a PA12 solution at a mass fraction of 5%-15%, with an average particle size of 50-100 nm. To break agglomeration, the mixture is subjected to high-frequency cavitation treatment for 20-30 minutes using an ultrasonic cell disruptor. The strong micro-jet shear force forces the nanoparticles to separate completely. At the same time, high-speed mechanical stirring at 1500-2000 rpm is used to ensure that the nano-alumina particles achieve an absolutely nanoscale monodisperse state in the PA12 matrix.

[0021] Preferably, the core load-bearing layer is made of high-strength carbon fiber unidirectional tape impregnated with toughened modified epoxy resin and laid in a [0 / ±45 / 90]s symmetrical layer. In the core area of ​​the mold, multiple layers of high-strength UD carbon unidirectional tape pre-impregnated with high-strength toughened epoxy resin are concentratedly laid according to a [0 / ±45 / 90]s balanced symmetrical layer matrix. Here, T800 unidirectional tape is used as an example, with a total thickness of about 3.1mm, accounting for 50%. Each layer is flattened to ensure that the fibers are arranged straight, without wrinkles or bubbles. By using high-strength UD carbon unidirectional tape in combination with toughened epoxy resin, 100% conversion of material mechanical properties is achieved. This layer, as the main load-bearing skeleton of the blade, has extremely high axial tensile strength and bending stiffness, and can withstand the centrifugal force field and aerodynamic bending moment generated under high-speed rotation of thousands of RPM. It controls the torsion and deflection deformation of the blade tip, ensures the conformity of the complex aerodynamic shape, and maintains the designed aerodynamic efficiency and noise reduction performance.

[0022] Preferably, in step 6, the stepped temperature-controlled pressurization includes: first heating to 80°C and holding at that temperature for 1 hour, then heating to 120-130°C at a rate of 1-2°C / min, applying a pressure of 0.3-0.5MPa and holding at that temperature for 3 hours. The mold is then placed in an autoclave and heated to 80°C and held at that temperature for 1 hour, allowing the toughened epoxy resin to reach its lowest viscosity point, exhibiting excellent fluidity and deeply wetting and penetrating every fiber bundle of carbon fiber and UHMWPE. Simultaneously, the surface PA12 begins to soften, and the interfacial molecular chains become active. Then, the temperature is steadily increased to between 120°C and 130°C at an extremely slow rate of 1-2°C / min, while simultaneously activating the autoclave pressurization system and applying a constant mechanical external pressure of 0.3 to 0.5MPa for 3 hours, achieving dense cross-linking of the epoxy resin and molecular-level interfacial bonding of the heterogeneous materials. Unlike conventional high-temperature (above 150℃) curing regimes, this method addresses the temperature resistance limits of polymer fibers such as UHMWPE by employing a stepped heating mechanism to achieve cross-linking and curing within the 120-130℃ range. This temperature range satisfies both the dense cross-linking of the toughened epoxy resin and the molecular-level bonding at the interface of heterogeneous materials, while effectively preventing crystal destruction and thermal degradation of the high-toughness fibers. This allows for the synergistic performance of the four heterogeneous components (carbon fiber, UHMWPE, PA12, and nano-alumina).

[0023] In step 6, slow cooling and shaping involves cooling the furnace to room temperature at a rate of less than 2°C / min to release the final minor crystallization stress. Detailed Implementation

[0024] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Example 1 Example 1 is the optimal example.

[0026] A 24-inch multi-rotor drone propeller aluminum alloy mold was selected, with a maximum thickness of 6.2mm at the propeller root. Nano-alumina particles with a particle size of 50-100nm were dispersed in PA12 solution at 10wt.%, and after ultrasonic dispersion, they were sprayed onto the leading edge area of ​​the mold with a coating thickness of 0.15mm. The coating was pre-baked at 90℃ for 30 minutes until it reached a semi-cured state. A mirror-symmetric layer is laid with the core load-bearing layer as a reference. The outermost layer is a PA12 prepreg tape doped with short-cut carbon fiber, with a thickness of 0.93 mm on one side and accounting for 15% of the total. Inward, a UHMWPE fiber fabric impregnated with toughened modified epoxy resin is laid, with a thickness of 0.62 mm on one side and accounting for 10% of the total. The core area uses T800 high-strength carbon fiber unidirectional tape symmetrically laid in [0° / ±45° / 90°]s, with a thickness of 3.1 mm and accounting for 50%. After mold closing, the vacuum is drawn to -0.098MPa and sent into a hot autoclave. The temperature is raised to 80℃ at 2℃ / min and held for 1 hour. Then the temperature is raised to 125℃, and a pressure of 0.4MPa is applied and held at a constant temperature and pressure for 3 hours. Then the temperature is slowly cooled to room temperature in the furnace at 1.5℃ / min. After demolding, the multi-rotor drone blades of layered carbon fiber composite material are obtained.

[0027] Performance test results: The tip deflection is 1.2 mm under full load at 8000 RPM; the outer layer breaks under 150J impact while the core remains intact, without overall separation; the mass loss is 12 mg under simulated wind and sand erosion (100 m / s, 2 hours); the structural damping loss factor tanδ=0.085; the macroscopic aerodynamic torsion angle deviation after curing is <0.1°.

[0028] Example 2 Example 2 is identical to Example 1 in terms of process steps and preparation parameters. The only difference is that the thickness ratio of each structural layer is adjusted as follows: the core bearing layer accounts for 60%, the built-in high-toughness crack arresting layer accounts for 10%, and the surface damping layer accounts for 30%.

[0029] Performance test results: The increased proportion of the core load-bearing layer increases the overall structural stiffness of the blade, and the elastic deflection of the blade tip decreases to 0.9 mm under full load at 8000 RPM; the structural crack arrest energy absorption threshold decreases slightly, and the blade shows deep tear marks under 120J impact load, but no overall fracture occurs; under the same wind and sand erosion conditions, the blade mass loss is 13 mg.

[0030] Example 3 Example 3 is identical to Example 1 in terms of structural layer ratio, layup method, and pre-preparation process. The only difference is that in the stepped temperature-controlled co-curing stage, the temperature of the second constant temperature platform is adjusted to 135°C.

[0031] Performance test results: The curing temperature approached the critical melting point of ultra-high molecular weight polyethylene fiber, and slight relaxation appeared in the microcrystalline region of the fiber; the elastic deflection of the paddle tip was 1.2 mm under full load at 8000 RPM; under 150 J impact load, the ultra-high molecular weight polyethylene fiber underwent partial necking fracture, and the tensile strength of the structure decreased slightly; the structural damping performance and wind and sand erosion resistance were basically the same as those in Example 1.

[0032] Comparative Example 1 (Traditional All-Carbon Fiber Baseline Scheme) Comparative Example 1 uses a traditional single composite material system without a leading edge nano-alumina wear-resistant reinforcement layer, surface damping layer, or built-in high-toughness crack arresting layer; the entire 6.2mm thick blade is made of conventional T300 carbon fiber woven fabric combined with ordinary epoxy resin and is formed using a conventional high-temperature constant temperature curing process at 150℃.

[0033] Performance test results: The blade structure has good rigidity, with a tip elastic deflection of 1.1 mm under 8000 RPM conditions; it experienced brittle avalanche fracture under only 55J low-energy impact load, and the blade completely broke into two pieces; under the same wind and sand erosion conditions, the mass loss was as high as 68 mg, the resin on the blade surface was severely peeled off, and the carbon fiber was exposed and frayed; the structural damping was extremely poor, with a damping loss factor tanδ of only 0.015, and a sharp howling noise was generated during high-speed operation.

[0034] Comparative Example 2 (excluding the built-in high-toughness crack arrest layer) Comparative Example 2 has the same preparation process and molding parameters as Example 1, except that the built-in high-toughness crack arresting layer with a thickness of 20% is removed. This part of the thickness is filled by the core bearing layer, so that the total thickness of the core bearing layer is increased to 70%.

[0035] Performance test results: The blade structure stiffness was further improved, and the blade tip elastic deflection was reduced to 0.8 mm under 8000 RPM conditions; due to the lack of a high elongation crack barrier formed by ultra-high molecular weight polyethylene fiber fabric, the crack could instantly penetrate the surface damping layer and the core bearing layer under 65J impact load, causing the blade to completely break; the wind and sand erosion resistance was the same as in Example 1, with a mass loss of 12 mg.

[0036] Comparative Example 3 (without surface damping layer and leading edge wear-resistant reinforcement layer) Comparative Example 3 has the same structure, layering, and curing process as Example 1. The difference is that the surface damping layer with a thickness of 30% and the leading edge nano alumina wear-resistant reinforcement layer are removed, so that the core load-bearing layer and the built-in high-toughness crack-resistant layer are directly exposed, and only conventional protective varnish is sprayed on the surface.

[0037] Performance test results: Under the action of the built-in high-toughness crack arresting layer, the blade did not break under the 130J impact load; however, due to the lack of surface damping and wear-resistant protection structure, the mass loss of wind and sand erosion surged to 75mg after 2 hours, the resin at the leading edge of the blade peeled off in a large area, and the internal fibers were exposed; the structural damping decreased significantly, the damping loss factor dropped to 0.018, and the high-frequency resonance phenomenon was significant during the flight of the UAV.

[0038] Comparative Example 4 (Aramid fiber replaced ultra-high molecular weight polyethylene fiber) Comparative Example 4 maintained the same structural ratios, layup methods, and preparation processes as Example 1, except that the ultra-high molecular weight polyethylene fiber fabric with a built-in high-toughness crack-arresting layer was replaced with an aramid fiber fabric.

[0039] Performance test results: The interfacial bonding performance between aramid fiber and epoxy resin matrix is ​​poor; under 90J impact load, the aramid fiber layer itself did not break, but severe macroscopic interlayer debonding occurred, causing the blade to lose bending stiffness instantly and fail; after being left to stand for a week in an 85% humidity environment, the moisture absorption mass of the blade increased by 2.5%, indicating poor moisture resistance.

[0040] Comparative Example 5 (Over-temperature curing exceeding the thermodynamic boundaries of the process) Comparative Example 5 has the same structural composition, layup method and pretreatment process as Example 1. The difference is that in the stepped temperature control co-curing stage, the temperature of the second constant temperature platform is set to 160°C, which exceeds the melting critical temperature of ultra-high molecular weight polyethylene fiber (usually between 144°C and 152°C).

[0041] Performance test results: High temperature caused the internal ultra-high molecular weight polyethylene fibers to completely thermodynamically melt and collapse, destroying the crystal orientation structure and completely failing the crack arrest function; the blades under 70J impact loads experienced overall brittle fracture, failing to meet the requirements for safe use.

[0042] Comparative Example 6 (Asymmetric ply, violating the mirror symmetry balancing rule) Comparative Example 6 uses the same materials, total thickness and manufacturing process parameters for each functional layer as Example 1. The difference is that the blade thickness direction does not use a mirror-symmetric structure for layering. The upper surface damping layer accounts for 10% of the thickness, the lower surface damping layer accounts for 20% of the thickness, and the functional layers are arranged asymmetrically.

[0043] Performance test results: Due to the mismatch in thermal expansion coefficients of heterogeneous materials, a large amount of residual internal stress was released after curing and demolding; the blades were significantly twisted and deformed, with an aerodynamic torsion angle error as high as 4.5°, resulting in severe aerodynamic failure. The blades could not be installed and put into actual use, and were directly scrapped.

[0044] Experimental data analysis and mechanism explanation A comparative analysis of Example 1 and Comparative Example 1 reveals that the UAV propeller blades employing a multiphase layered composite structure, while maintaining a principal shaft stiffness comparable to existing blades made of single carbon fiber material, significantly improve the blade's fracture impact threshold, substantially reduce wind and sand erosion mass loss, and achieve a multiple-fold improvement in structural damping performance. This demonstrates that the present invention, through a heterogeneous functional layer composite design, achieves a multi-dimensional synergistic coupling of rigidity, toughness, damping, and surface wear resistance, exhibiting significant comprehensive mechanical performance advantages compared to traditional single-material blades.

[0045] Through comparative analysis of Example 1 with Comparative Examples 2, 4, and 5, the irreplaceable nature of ultra-high molecular weight polyethylene fiber in the built-in high-toughness crack arresting layer and the strict constraints of the molding temperature control process can be clearly demonstrated. Comparative Example 2, which eliminates the UHMWPE fiber crack-arresting structure, exhibits brittle shear fracture under relatively low impact loads. In contrast, the proposed solution maintains overall structural integrity under high impact loads, demonstrating that UHMWPE fiber is a key core structure for constructing blade damage tolerance and achieving crack arrest and energy absorption. Comparative Example 4, which uses aramid fiber instead of UHMWPE fiber, suffers from severe interlaminar debonding failure due to the poor interfacial compatibility between aramid fiber and the resin matrix. Furthermore, the material's high hygroscopicity makes it unsuitable for the complex outdoor service conditions of UAVs. This further confirms that UHMWPE fiber is the preferred material that balances low density, high fracture energy absorption, and good interfacial bonding with modified epoxy resin. Comparative Example 5, which uses ultra-high temperature curing, shows that traditional high-temperature curing processes destroy the crystal structure of UHMWPE fiber, causing fiber performance collapse and complete failure of the crack arrest and energy absorption mechanism. The stepped temperature-controlled pressure curing process specified in this application is a necessary process condition to ensure the stable molding of the composite material's structure and performance.

[0046] Comparing the test results of Example 1 and Comparative Example 3, it can be seen that after removing the surface damping layer and the leading-edge nano-alumina wear-resistant reinforcement layer, the blade's resistance to wind and sand erosion and structural damping performance both showed a significant decrease, the mass loss from wind and sand erosion increased substantially, and the structural damping loss factor decreased significantly. This indicates that the PA12 thermoplastic composite material doped with short-cut carbon fibers dissipates vibrational energy through macromolecular chain friction and interfacial slip. Combined with the protective effect of the leading-edge nano-alumina hard wear-resistant reinforcement layer, it can effectively suppress blade leading-edge erosion and wear, maintain aerodynamic shape and dynamic balance stability, and reduce structural vibration and operating noise. It is an important protective structure for improving the blade's weather resistance and operational reliability.

[0047] The test results of Comparative Example 6 show that there are differences in the coefficient of thermal expansion among the different functional heterogeneous composite materials. If the blade layup structure does not follow the principle of mirror symmetry in the thickness direction, the residual internal stress cannot be released uniformly during the curing and cooling process, which can easily lead to structural coupling stiffness imbalance, causing the blade to undergo significant torsional deformation and the aerodynamic shape accuracy to seriously exceed the standard, which cannot meet the actual installation and use requirements. This fully verifies the necessity of adopting the mirror symmetric layup structure design and the symmetrical layup process steps in this application for controlling molding deformation and ensuring the aerodynamic performance of the blade.

[0048] The core of this application is to balance the contradiction between the curing requirements of epoxy resin and the thermal stability of heat-sensitive fibers (UHMWPE, PA12). Specifically, in the stepped temperature control strategy, 80℃ is used for initial curing and degassing, and 120-130℃ is used for pressure crosslinking. This temperature range avoids the melting point of ultra-high molecular weight polyethylene fibers (melting point approximately 130-136℃), ensuring that the toughened epoxy resin completes dense crosslinking at medium temperature while preventing the UHMWPE crack arrestor layer from undergoing crystal destruction due to overheating. The data from Example 5, which showed that the fiber melted and collapsed due to overheating curing at 160℃, verifies the necessity of the 120-130℃ temperature window. For the PA12-based wear-resistant layer, pre-baking at 80-100℃ brings it to a semi-cured (B-stage) state, which locks the leading edge structure and does not affect subsequent interface fusion. Slow cooling at a rate below 2℃ / min is used to release residual stress and control dimensional accuracy, while the pretreatment with release agent at 60-80℃ is the conventional temperature range for semi-permanent release agent film formation. In summary, the numerical settings in the document are based on the thermodynamic properties of the materials and the adaptability to the process, and the theoretical basis and engineering rationality are valid.

[0049] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A multi-rotor drone blade made of layered carbon fiber composite material, characterized in that, The blade adopts a functionally graded layered composite structure, consisting of a core load-bearing layer, a built-in high-toughness crack arresting layer symmetrically arranged on the upper and lower sides of the core load-bearing layer, and a surface damping layer symmetrically arranged on the outside of the built-in high-toughness crack arresting layer from the inside out. The blade leading edge area of ​​the surface damping layer is provided with a nano-alumina wear-resistant reinforcement layer, and the blade as a whole has a mirror symmetrical structure along the center of thickness.

2. The multi-rotor UAV blade made of layered carbon fiber composite material according to claim 1, characterized in that, The core load-bearing layer is composed of high-strength carbon fiber unidirectional tape and toughened modified epoxy resin; the built-in high-toughness crack arresting layer is composed of ultra-high molecular weight polyethylene fiber fabric and the same resin system; the surface damping layer is PA12 composite material doped with short-cut carbon fibers.

3. The multi-rotor UAV blade made of layered carbon fiber composite material according to claim 1 or 2, characterized in that, The core load-bearing layer accounts for 50% of the total blade thickness; the built-in high-toughness crack arresting layer accounts for 10% of the total blade thickness on one side; and the surface damping layer accounts for 15% of the total blade thickness on one side.

4. A method for preparing the multi-rotor drone blades of layered carbon fiber composite material as described in claim 1, 2, or 3, characterized in that, Includes the following steps: Step 1: Pre-treat the lower mold cavity and the upper mold cavity respectively. Prepare wear-resistant reinforcement layers in the leading edge areas of the blades corresponding to the lower mold and the upper mold, and bake them to a semi-cured state to complete the leading edge reinforcement of the lower mold and the upper mold. Step 2: Lay the lower surface damping layer inside the lower mold cavity where the leading edge has been reinforced; Step 3: Lay the underlying high-toughness crack arresting layer on the lower surface damping layer; Step 4: Lay the core load-bearing layer on the lower built-in high-toughness crack arrest layer; Step 5: Using the core load-bearing layer as a reference, and following the principle of mirror symmetry, lay the upper built-in high-toughness crack arresting layer and the upper surface damping layer in sequence. Step 6: Close the upper and lower molds and evacuate them. Use stepped temperature control and pressure to perform integrated co-curing. After slow cooling and shaping, demold to obtain the multi-rotor drone blades made of layered carbon fiber composite material.

5. The method for preparing the multi-rotor UAV blades of layered carbon fiber composite material according to claim 4, characterized in that, The wear-resistant reinforcing layer is made by dispersing nano-alumina particles in PA12 solution at a mass fraction of 5%-15%, with an average particle size of 50-100nm.

6. The method for preparing the multi-rotor UAV blades of layered carbon fiber composite material according to claim 4 or 5, characterized in that, When baking the wear-resistant reinforcement layer, the baking temperature is 80℃-100℃ and the baking time is 20-40 minutes.

7. The method for preparing the multi-rotor UAV blades of layered carbon fiber composite material according to claim 4 or 5, characterized in that, The core load-bearing layer is made of high-strength carbon fiber unidirectional tape impregnated with toughened modified epoxy resin and adopts [0 / ±45 / 90]s symmetrical layup.

8. The method for preparing the multi-rotor UAV blades of layered carbon fiber composite material according to claim 4 or 5, characterized in that, In step 6, the stepped temperature control pressurization includes: first heating to 80℃ and holding at that temperature for 1 hour, then heating to 120-130℃ at a rate of 1-2℃ / min, applying a pressure of 0.3-0.5MPa and holding at that temperature and pressure for 3 hours.

9. The method for preparing the multi-rotor UAV blades of layered carbon fiber composite material according to claim 4 or 5, characterized in that, In step 6, slow cooling and shaping involves cooling the furnace to room temperature at a rate of less than 2°C / min.

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