Application of bamboo fibers in unmanned aerial vehicle

Abstract

The invention discloses application of bamboo fibers in an unmanned aerial vehicle, belongs to the technical field of composite material processing and production, and aims at load characteristics (high specific strength and high specific stiffness) of consumer-level unmanned aerial vehicles, the mechanical property characteristics of mechanical orthotropic properties in the directions of bamboo fibers and vertical fibers are considered, and the load characteristics (high specific strength and high specific stiffness) of the consumer-level unmanned aerial vehicles are improved. The innovative application of the bamboo material on the consumption-level unmanned aircraft with the weight of less than 25 kilograms is realized, and the requirement of the consumption-level unmanned aircraft with the weight of less than 25 kilograms on the low-cost material is met.

Description

Technical Field

[0001] The invention belongs to the technical field of composite material processing and production, and in particular relates to an application of bamboo fiber in a drone. Background Art

[0002] Bamboo is a natural organic fiber-reinforced composite material with good specific strength and specific stiffness. It is comparable to existing steel materials in some mechanical parameters. It has a short growth cycle and low cost, and is widely used in construction materials, office furniture and other fields. However, bamboo materials have not yet been introduced on a large scale in the aviation field, mainly because its mechanical properties and chemical properties are difficult to meet the requirements of previous aircraft application scenarios. A large number of consumer-grade drones have entered the field of public life, such as aerial photography drones, drone swarm performances and other application scenarios have been widely known. However, most of the current drones use traditional carbon fiber composite materials or plastics, and their production process and final recycling are relatively environmentally friendly.

[0003] The current market size of consumer drones is very large. Their flight speed is mainly below 60km / h. They mostly use multi-rotor flight mode, so the flight load is relatively small, and the bearing stress of general structural materials is 50Mpa. In order to pursue lighter weight, existing manufacturers in the market use carbon fiber composite materials or plastics. If they are damaged and cannot be repaired, they are often directly landfilled or incinerated as non-recyclable garbage, causing a lot of pollution. The bearing stress of bamboo structures is 60Mpa-70Mpa, which just meets the demand, and as a degradable material, the environmental problems caused are very small.

[0004] The main load-bearing structural materials of current consumer-grade unmanned aerial vehicles are mainly plastics, carbon fiber composite materials and other lightweight materials to achieve load-bearing flight. However, the production process and the final recycling process will generate a lot of pollution and energy consumption. For example, plastics generally cannot be naturally degraded, and carbon fiber manufacturing requires a high temperature and high pressure environment. The current technology can only be recycled through landfill or incineration when the two materials are finally processed. The above treatment methods are relatively polluting to the environment.

[0005] The use of bamboo materials in the aviation field is still in its infancy, because aircraft design places high demands on the mechanical properties per unit weight. Summary of the invention

[0006] In view of the load characteristics (high specific strength and high specific stiffness) of consumer-grade unmanned aerial vehicles, the present invention takes into account the mechanical properties of mechanical orthogonality along bamboo fibers and perpendicular to the fiber directions, and realizes the innovative application of bamboo materials in consumer-grade unmanned aerial vehicles below 25 kilograms, thus solving the demand for low-cost materials for consumer-grade unmanned aerial vehicles below 25 kilograms.

[0007] The present invention provides an application of bamboo fiber in a drone, including:

[0008] The application of bamboo fiber in the main load-bearing parts of consumer drones weighing less than 25 kg;

[0009] and / or the use of bamboo fiber in connectors for consumer drones weighing less than 25 kg.

[0010] As a preferred embodiment of the present technical solution, the main load-bearing parts include wings, multi-rotor support parts, landing gear, propellers and casing.

[0011] As a preferred embodiment of the present technical solution, the bamboo material can be made into main load-bearing parts or connecting parts through cutting, designing, drying, baking, moisture-proofing and other processes.

[0012] The present invention also provides an application of bamboo fiber in the material of the main load-bearing parts of a consumer-grade drone weighing less than 25 kilograms.

[0013] The present invention also provides an application of bamboo fiber in preparing a main load-bearing component of a consumer-grade drone weighing less than 25 kilograms.

[0014] Compared with the prior art, the present invention has the following advantages:

[0015] Bamboo materials are not only easy to obtain but also inexpensive. When used in consumer drones, they can meet the requirements of consumer aircraft for structural strength, light weight and other materials. Compared with carbon fiber composite materials, their costs are greatly reduced. At the same time, bamboo materials, as degradable materials, can effectively reduce carbon emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is the relationship graph between stress and strain.

[0017] Figure 2 It is a three-dimensional simulation of a bamboo tube.

[0018] Figure 3 It is a cross-section diagram of a bamboo tube ring.

[0019] Figure 4 This is a simulation diagram of the cross section of a bamboo tube.

[0020] Figure 5 This is the stress result diagram of a bamboo tube with a transverse circular hole.

[0021] Figure 6 It is a simplified force model of the cantilever beam of a UAV.

[0022] Figure 7 This is a photo of an electronic universal testing machine.

[0023] Figure 8It is a side view of a 2mm bamboo board.

[0024] Fig. 9 It is a top view of the tensile test piece.

[0025] Fig.10 It is a schematic diagram of the clamping of the tensile test piece.

[0026] Fig.11 This is a diagram of the fracture effect of the tensile test piece.

[0027] Fig.12 It is the fracture change curve diagram of the stretched longitudinal grain group 1.

[0028] Fig.13 It is the fracture change curve diagram of the stretched longitudinal grain group 2.

[0029] Fig.14 Top view of the shear test piece.

[0030] Fig.15 It is a schematic diagram of the clamping of the shear test piece.

[0031] Fig.16 This is a diagram of the fracture effect of the shear test piece.

[0032] Fig.17 is the stress variation of shear group 1.

[0033] Fig.18 is the stress variation of shear group 2. DETAILED DESCRIPTION

[0034] The present invention is further described below with reference to specific examples.

[0035] Related analysis of mechanical properties of bamboo materials:

[0036] 1. Concept of destructive strength

[0037] 1.1 Calculation of failure strength

[0038] (1) Comparison formula

[0039] First calculate the stress and strain:

[0040] σ=F÷A

[0041] ε=ΔL÷L

[0042] In the above formula,

[0043] σ: stress

[0044] F: the force on the object

[0045] A: The area of ​​the object under force

[0046] ε: strain

[0047] ΔL: The change in length of an object after a force is applied

[0048] L: original length of the object

[0049] The way to judge whether an object is damaged is to compare the stress on the object with the damage stress σ b However, in the relationship between strain and stress of an object, the object first undergoes elastic changes and then plastic changes. After reaching a critical value, the stress will grow very slowly with the strain. Therefore, the critical value can be used to judge whether the object is damaged. The critical value of stress is called the yield stress σ s .

[0050] (2) The relationship between stress and strain is shown in the figure Figure 1 As shown in the figure, in the relationship between strain and stress of an object, the object first undergoes elastic changes and then plastic changes. After reaching a critical value, the stress will become very slow as the strain increases.

[0051] 2. Material strength verification

[0052] Mainly carry out strength check on the arms of multi-rotor aircraft.

[0053] The arm is subject to a torque generated by the pull of the rotor on the arm. The calculation method of this torque is: first determine the load of our multi-rotor. For example, the maximum take-off weight of the aircraft we make is 6 kg, and it is a six-rotor aircraft. Then each arm will be subject to a maximum force of 1 kg, about 10 Newtons. This force multiplied by the length of the arm is the torque on the arm, such as Figure 2 shown.

[0054] The effect of this moment is to bend the arm. The maximum bending stress is calculated by dividing the moment by the section modulus. The section modulus formula is:

[0055]

[0056] α=d / D

[0057] like Figure 3 As shown, D is the major diameter of the ring; d is the minor diameter of the ring; W x W: bending section modulus of the cross section with respect to the x-axis; y : Bending section modulus of the section about the y-axis.

[0058] The torque is related to both the outer diameter D and the inner diameter d of the bamboo tube, so we need to know the inner and outer diameters of the bamboo tube used, such as Figure 4As shown. After calculating the maximum bending stress, we should compare it with the allowable stress of the material. If the maximum bending stress is less than the allowable stress, it is reasonable. Taking into account that the individual differences of bamboo materials may be large, our allowable stress is the maximum yield stress of the bamboo material divided by 1.5. After that, considering that our bamboo tube needs to be punched, we also need to check whether the stress of the dangerous section is less than the allowable stress. The radius of the hole we punched is about 0.05 larger than the outer diameter of the bamboo tube. From the chart, we can see that our dangerous section stress concentration factor is 3, which means that a stress three times the above-mentioned calculated stress may be generated here, and it still needs to be less than the allowable stress of the bamboo material, such as Figure 5 So far, we have completed the theoretical strength verification of the arm.

[0059] Since the above is a theory, we are not sure whether the maximum yield stress of our bamboo material is still as high as the theoretical value after punching holes, so we punch holes in bamboo boards and carbon fiber boards and conduct comparative tests. The test method is to cut the board into the required size and punch holes, then pass a pin through the hole, and conduct a tensile test to measure the maximum yield stress, and divide it by 1.5 to get the allowable stress.

[0060] In this way, we can understand whether the allowable stress of bamboo materials is significantly different from the theory to guide us in making aircraft, and we can also compare the strength difference between bamboo materials and carbon fiber materials after punching.

[0061] 3. Poisson's ratio, Young's modulus, shear modulus

[0062] ε x / ε y =μ

[0063] σ / ε=E

[0064] τ / ε=G

[0065] In the above formula, Poisson's ratio μ refers to the transverse normal strain ε when the material is subjected to unidirectional tension or compression. x and axial normal strain ε y The ratio of stress σ to strain ε is also called the transverse deformation coefficient, which is an elastic constant reflecting the transverse deformation of the material. The ratio of stress σ to strain ε is called Young's modulus E. Young's modulus measures the stiffness of an isotropic elastic body and is defined as the ratio between uniaxial stress and uniaxial deformation within the range where Hooke's law applies.

[0066] Shear modulus is the ratio of shear stress to strain. It is also called shear modulus or rigidity modulus. It is one of the mechanical properties of materials. It characterizes the ability of materials to resist shear strain. A large modulus indicates a strong rigidity of the material.

[0067] Young's modulus E, shear modulus G, bulk modulus K, and Poisson's ratio ν can be converted using the formula: E=2G(1+v)=3K(1-2v).

[0068] Bamboo fiberboard longitudinal tensile static strength load test

[0069] Design a simplified force model of the UAV cantilever beam, such as Figure 6 As shown, the cantilever should satisfy: lifting moment F1*L=couple moment F2*R. Therefore, it is necessary to carry out a bamboo fiberboard static strength load test on the material to verify whether the material can withstand the maximum force required.

[0070] Experimental methods:

[0071] 1. Instruments and Equipment

[0072] like Figure 7 As shown, an electronic universal testing machine is used.

[0073] 2. Clamping design

[0074] By cutting out the thicker parts at both ends as reinforcement sheets to assist clamping, the breaking part can be controlled to be located in the middle.

[0075] 3. Bamboo board size

[0076] The bamboo board has the same plane except for the reinforcement sheet, and the thickness is 2mm. The top view and side view are as follows: Figure 8 and Fig. 9 shown.

[0077] The overall schematic diagram of the clamping method and the fracture effect is as follows Fig.10 and Fig.11 As shown, the reinforcing plates at both ends of the bamboo fiberboard are clamped on the upper and lower clamps of the electronic universal testing machine respectively, and the strain gauge is connected to the strain measuring device. After the load is applied to the yield load, the bamboo board begins to break from the center part.

[0078] 4. Experimental Notes

[0079] (1) Draw reference lines on the surface of the bamboo board and the fixture to ensure that the bamboo board and the fixture are placed in the middle of the testing machine clamp.

[0080] (2) Before conducting the experiment, make sure that the bamboo board is not twisted.

[0081] (3) To avoid slipping during the experiment, the fixture can be properly polished.

[0082] (4) When attaching strain gauges, it is necessary to determine the horizontal and vertical center lines of the bamboo board, and attach the gauges near the horizontal and vertical centers respectively. The gauges need to be attached on both sides to reduce the error.

[0083] The results of multiple stretching are as follows Figure 12-13 As shown, the results were fitted linearly, and the Logistic regression equations of the stretch longitudinal grain group 1 and the stretch longitudinal grain group 2 were: y = 0.0326x + 15.039, R 2 =0.9994;y=0.0352x+8.3534,R 2 =0.9995. From E=σ / ε, we can know that the slope of the straight line is the elastic modulus, E1=32.6GPa, E2=35.2GPa, and the average value is E=33.9GPa. The experimental results are within the elastic modulus range of 28-79GPa of bamboo fiber, which can be applied to consumer-grade drones. According to the requirements of the designed consumer-grade drones, through weaving, cutting design, drying, baking, moisture-proof treatment and other processes, the structural strength and lightness of the material of consumer-grade aircraft are met.

[0084] Bamboo fiberboard 45° direction shear strength load test

[0085] Design a simplified force model of the UAV cantilever beam, such as Figure 6 As shown, the cantilever should satisfy: lifting moment F1*L=couple moment F2*R. Therefore, it is necessary to carry out a bamboo fiberboard static strength load test on the material to verify whether the material can withstand the maximum force required.

[0086] Experimental methods:

[0087] 1. Instruments and Equipment

[0088] like Figure 7 As shown, an electronic universal testing machine is used.

[0089] 2. Clamping design

[0090] By cutting out the thicker parts at both ends as reinforcement sheets to assist clamping, the breaking part can be controlled to be located in the middle.

[0091] 3. Bamboo board size

[0092] The bamboo board has the same plane except for the reinforcement sheet, and the thickness is 2mm. The top view and side view are as follows: Figure 8 and Fig.14 shown.

[0093] The overall schematic diagram of the clamping method and the fracture effect is as follows Fig.15 and Fig.16 As shown, the reinforcing plates at both ends of the bamboo fiberboard are clamped on the upper and lower clamps of the electronic universal testing machine respectively, and the strain gauge is connected to the strain measuring device. After the load is applied to the yield load, the bamboo board begins to break near the center.

[0094] 4. Experimental Notes

[0095] (1) Draw reference lines on the surface of the bamboo board and the fixture to ensure that the bamboo board and the fixture are placed in the middle of the testing machine clamp.

[0096] (2) Before conducting the experiment, make sure that the bamboo board is not twisted.

[0097] (3) To avoid slipping during the experiment, the fixture can be properly polished.

[0098] (4) When attaching strain gauges, it is necessary to determine the horizontal and vertical center lines of the bamboo board, attach the strain gauges at the horizontal and vertical centers, and attach the gauges on both sides to reduce errors.

[0099] The results of multiple shearing are as follows Figure 17-18 As shown, the results were fitted with a straight line, and the Logistic regression equations of shear group 1 and shear group 2 were:

[0100] y=0.0184x+5.4021,R 2 =0.9788;y=0.0125x+3.3968,R 2 = 0.9956. From G = τ / ε, we can know that the slope of the straight line is the shear modulus G1 = 18.4 GPa, G2 = 12.5 GPa, and the average value is G = 15.45 GPa. The experimental results show.

[0101] After consulting the data, the mechanical properties of bamboo fiber are shown in the following table:

[0102] Material Type Tensile strength / MPa Elastic modulus / GPa <![CDATA[Specific strength / [MPa / (g / cm 3 )]]]> Bamboo Fiber 410-590 28-79 320-580

[0103] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention, rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. An application of bamboo fiber in drones.

2. The use according to claim 1, characterized in that The application of bamboo fiber in the main load-bearing parts of consumer-grade drones weighing less than 25 kg.

3. The use according to claim 1, characterized in that The application of bamboo fiber in connectors for consumer drones weighing less than 25 kg.

4. An application of bamboo fiber in the material of the main load-bearing parts of consumer-grade drones below 25 kg.

5. An application of bamboo fiber in the preparation of main load-bearing parts for consumer-grade drones weighing less than 25 kilograms.

6. The use according to claim 4, characterized in that The tensile strength of bamboo fiber is 410-590MPa, the elastic modulus is 28-79GPa, and the specific strength is 320-580MPa / (g / cm 3 ).

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