Composite material paddle reliability analysis method

Abstract

The invention provides a reliability analysis method for a composite paddle. The reliability analysis method comprises the following steps: S1, carrying out modeling and finite element analysis on the paddle according to a carbon fiber laying condition of the paddle; s2, carrying out a loading test on the composite material paddle; s3, measuring detailed statistical characteristic parameters of the composite material blade; s4, constructing a composite material paddle structure performance function by using a polynomial response surface method; and S5, calculating the obtained limit state function of the composite material blade to obtain the reliability of the blade. According to the method, finite element simulation is combined with a test, so that reliability analysis is closer to an actual situation; only one test is needed for calculating the reliability of the composite paddle structure, the reliability test frequency is effectively reduced, the test cost is reduced, and the calculation efficiency is improved; the finally constructed paddle structure performance function can analyze the influence degree of each parameter on the performance of the paddle structure, and has a certain guiding effect on the design of the composite material paddle structure.

Description

Technical Field

[0001] The invention relates to the technical field of aviation vehicles, and in particular to a reliability analysis method for composite material blades. Background Art

[0002] In the classic design of blade structures, any design that satisfies the requirement that the equivalent stress of the structure is less than the required stress of the material is considered reliable, with a reliability of 100%. However, as the application environment becomes more severe and material parameters and dimensional errors exist, the equivalent stress of the structure and the required stress of the material are not constant, and the structure of the classic design may not meet the safety requirements. The sampling method can solve various complex engineering problems, but generally complex engineering problems need to be analyzed by experiments or finite element methods, which is a complex and time-consuming process. Summary of the invention

[0003] The purpose of the present invention is to provide a reliability analysis method for composite blades, which can effectively reduce the number of reliability tests, reduce test costs, improve calculation efficiency, and ensure the safety performance of composite blades.

[0004] According to one object of the present invention, the present invention provides a reliability analysis method for a composite material blade, comprising the following steps:

[0005] S1. Modeling and finite element analysis of the blades according to their carbon fiber layup conditions;

[0006] S2. Carry out loading test on composite blades;

[0007] S3. Measure detailed statistical characteristic parameters of composite blades;

[0008] S4. Use polynomial response surface methodology to construct composite blade structural performance functions;

[0009] S5. Calculate the limit state function of the composite material blade obtained to obtain the blade reliability.

[0010] Furthermore, in S1, when performing finite element simulation, the finite element simulation load is the centrifugal force and aerodynamic force exerted on the composite blade in the in-situ working condition, and the finite element simulation calculates the maximum value of the blade stress and strain.

[0011] Furthermore, in S2, the loading test has the same load as the finite element simulation load, and it is necessary to stick a strain gauge on the composite blade to obtain the maximum stress value and compare it with the finite element simulation to verify the validity of the above finite element simulation.

[0012] Furthermore, in S2, the device for performing a loading test on a composite blade comprises a blade root fixing device, a composite blade, a Y-axis loading hydraulic cylinder, a Y-axis loading sensor, an X-axis loading hydraulic cylinder and an X-axis loading sensor, wherein the blade root fixing device is used to fix the composite blade, the Y-axis loading hydraulic cylinder is connected to the composite blade through a blade-specific tooling, the X-axis loading hydraulic cylinder is connected to the composite blade through a wire rope, and the X-axis loading sensor is connected to the X-axis loading hydraulic cylinder.

[0013] Furthermore, in S3, the characteristic parameters are determined by the following method:

[0014] Since the centrifugal force that the blades bear during flight is much greater than other loads, it has the greatest impact on the external load effect S of the blades. The main considerations are the related uncertainty variables that affect the centrifugal force, namely the blade mass and the position of the blade center of gravity. The propeller speed has a great influence on each load, so it is given priority consideration. The resistance R of the structure itself mainly depends on the material properties of the blades, namely the allowable strain of the carbon fiber.

[0015] Furthermore, the state of the structure is judged by comparing the size of the structural resistance and the load effect. The condition that should be met for its safe operation is: Z=RS≥0.

[0016] Furthermore, in S4, the polynomial response surface method needs a large amount of data to construct the performance function. According to the probability density function and cumulative distribution function of the above three variables, three probability level points are extracted for each random variable, and then 13 sample points including the midpoints of the edges and the center points are selected, and the response values ​​of these sample points, i.e., the maximum strain value, are simulated and calculated.

[0017] Further, in S4, the method for constructing the blade structure function function is: applying the least square method to fit and analyze the influence of three random variables on the response value, and obtaining the response surface function of the composite material blade structure failure, that is, the blade structure function function;

[0018] Further, in S5, the reliability of the composite blade is obtained by calculating the constructed blade structure performance function using a first order second moment method.

[0019] Furthermore, the basic principle of the first-order second moment method uses the mean value and standard deviation of random variables to solve the reliability index β of the structure, and expands the limit state equation at the center point according to the Taylor series, where:

[0020]

[0021] The technical solution of the present invention combines finite element simulation with experiments to make the reliability analysis closer to the actual situation; only one test is required to calculate the reliability of the composite blade structure, which effectively reduces the number of reliability tests, reduces the test cost, and improves the calculation efficiency; the blade structure function function finally constructed can analyze the influence of each parameter on the blade structure performance, which has a certain guiding role in the design of composite blade structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 A flow chart of the method implemented by the present invention;

[0024] Figure 2 It is a schematic diagram of the structure of the blade loading test device implemented in the present invention;

[0025] Figure 3 A distribution diagram of sample points selected during the implementation of the present invention;

[0026] In the figure: 1. Blade root fixing device; 2. Composite material blade; 3. Y-axis direction loading hydraulic cylinder; 4. Y-axis direction loading sensor; 5. X-axis direction loading hydraulic cylinder; 6. X-axis direction loading sensor. DETAILED DESCRIPTION

[0027] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0029] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "multiple" means two or more, unless otherwise clearly and specifically defined. In addition, the terms "installed", "connected" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0030] Example 1

[0031] like Figure 1 As shown,

[0032] A reliability analysis method for composite blades comprises the following steps:

[0033] S1. Modeling and finite element analysis of the blades according to their carbon fiber layup conditions;

[0034] In S1, the finite element analysis loads are centrifugal force and aerodynamic force. The centrifugal force is calculated based on the rotational speed, mass and center of gravity, and then the blade thrust value is obtained by the actual rotational speed of the blade and the wind tunnel test measurement;

[0035] S2. Carry out loading test on composite blades;

[0036] The above loads are applied to the blade model. Since the stiffness of the layers in different directions of the composite material structure is different, each layer will have different stresses, and its strain is independent of the orientation of the layer. Therefore, compared with the metal structure, the strain analysis is more focused on its strain. Therefore, the maximum position and maximum value of the composite blade strain are finally extracted.

[0037] According to the above finite element simulation results, strain gauges are pasted on the composite blades, and several sets of strain gauges are pasted at other different positions to compare the test and simulation results and verify the consistency;

[0038] like Figure 2As shown, a device for performing a loading test on a composite blade comprises a blade root fixing device 1, a composite blade 2, a Y-axis direction loading hydraulic cylinder 3, a Y-axis direction loading sensor 4, an X-axis direction loading hydraulic cylinder 5 and an X-axis direction loading sensor 6; the blade root fixing device 1 is used to fix the composite blade 2, the Y-axis direction loading hydraulic cylinder 3 is connected to the composite blade 2 through a blade specific tooling, and is used to provide blade thrust; the X-axis direction loading hydraulic cylinder 5 is connected to the composite blade 2 through a wire rope, and is used to provide blade centrifugal force; the X-axis direction loading sensor 6 is connected to the X-axis direction loading hydraulic cylinder 5.

[0039] S3. Measure detailed statistical characteristic parameters of composite blades;

[0040] In S3, the characteristic parameters considered are: In engineering practice, the safety analysis of blade structures needs to consider two factors: one is the external load effect S, that is, the strain caused by the load; the other is the resistance R of the structure itself, that is, the allowable strain of the carbon fiber material. The functional function Z of the structure can be expressed as an expression of the external load effect S and the structural resistance R. By comparing the size of the structural resistance and the load effect to judge the state of the structure, it can be known that the conditions that should be met for its safe operation are:

[0041] Z=RS≥0;

[0042] S4. Use polynomial response surface methodology to construct composite blade structural performance functions;

[0043] The random differences in propeller speed, high altitude environment, and molded blade structure during flight will cause the external load effect S to be random. Due to the differences in different parts of the material, specimen processing, molded state, test environment, and personnel, the structural resistance R of the same material also shows dispersion. Therefore, the external load effect S and the structural resistance R are two independent random variables. According to the stress-strength interference theory, the overlapping part of the two probability density functions is the interference area. At this time, Z<0, that is, the structure fails, and the corresponding probability is the structural failure rate.

[0044] The polynomial response surface method is used to construct the performance function of the composite blade structure. The basic idea is to fit the discrete data with an approximate method, and replace the original complex calculation model with a mathematical model with small calculation amount and high accuracy. By extracting three probability level points for each random variable, and combining the edge midpoint and the center point according to certain rules as sample points, such as Figure 3 As shown, the probability level point of a random variable with any distribution can be determined by the following formula;

[0045] in:

[0046] p is the probability level;

[0047] In order to obtain the response value of each group of random variables, that is, the maximum strain value, it is necessary to perform finite element analysis on the above 13 sample points. Finally, the sample point data is used as the input value, the maximum strain value is used as the response value, and the least squares method is used to fit and analyze the influence of the three random variables on the response value, and the functional function of the composite blade structure failure is obtained;

[0048] S5. Calculate the obtained limit state function of the composite material blade to obtain the blade reliability.

[0049] The obtained function is calculated using the first-order second moment method. The basic principle of the first-order second moment method is to use the mean value and standard deviation of random variables to solve the reliability index β of the structure and expand the limit state equation at the center point according to the Taylor series. Among them:

[0050] in:

[0051] β is the reliability index of the structure, Z is the structural performance function, μ is the mean value, and σ is the standard deviation.

[0052] Therefore, in order to ensure the safety performance of equipment with complex structures, the influence of random factors such as environment, structure, and materials on the mechanical properties of engineering structures is comprehensively considered. The reliability analysis method of composite blades proposed in the present invention can effectively reduce the number of reliability tests, reduce test costs, and improve calculation efficiency, and it also plays a certain guiding role in the optimal design of engineering structures.

[0053] The present invention combines finite element simulation with experiments to make reliability analysis closer to actual conditions; only one test is required to calculate the reliability of the composite blade structure, which effectively reduces the number of reliability tests, reduces test costs, and improves calculation efficiency; the blade structure function function finally constructed can analyze the influence of each parameter on the blade structure performance, which has a certain guiding role in the design of composite blade structures.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A reliability analysis method for composite blades, characterized in that: The following steps are involved: S1. Modeling and finite element analysis of the propeller blade according to its carbon fiber layup conditions; S2. Carry out loading test on composite blades; S3. Measure detailed statistical characteristic parameters of composite blades; S4. Use polynomial response surface methodology to construct composite blade structural performance functions; S5. Calculate the limit state function of the composite material blade obtained to obtain the blade reliability.

2. The composite blade reliability analysis method according to claim 1, characterized in that: In S1, when the finite element simulation is performed, the finite element simulation load is the centrifugal force and aerodynamic force exerted on the composite blade in the in-situ working condition, and the finite element simulation calculates the maximum value of the blade stress and strain.

3. The reliability analysis method of composite blades according to claim 1, characterized in that: In S2, the loading test is the same as the finite element simulation load. It is necessary to stick strain gauges on the composite blades to obtain the maximum stress value and compare it with the finite element simulation to verify the validity of the above finite element simulation.

4. The reliability analysis method of composite blades according to claim 1, characterized in that: In S2, a device for performing a loading test on a composite blade includes a blade root fixing device, a composite blade, a Y-axis loading hydraulic cylinder, a Y-axis loading sensor, an X-axis loading hydraulic cylinder and an X-axis loading sensor, wherein the blade root fixing device is used to fix the composite blade, the Y-axis loading hydraulic cylinder is connected to the composite blade through a blade-specific tooling, the X-axis loading hydraulic cylinder is connected to the composite blade through a wire rope, and the X-axis loading sensor is connected to the X-axis loading hydraulic cylinder.

5. The reliability analysis method of composite blades according to claim 1, characterized in that: In S3, the characteristic parameters are determined by the following method: Since the centrifugal force that the blades bear during flight is much greater than other loads, it has the greatest impact on the external load effect S of the blades. The main considerations are the related uncertainty variables that affect the centrifugal force, namely the blade mass and the position of the blade center of gravity. The propeller speed has a great influence on each load, so it is given priority consideration. The resistance R of the structure itself mainly depends on the material properties of the blades, namely the allowable strain of the carbon fiber.

6. The reliability analysis method of composite blades according to claim 1, characterized in that: The state of the structure is judged by comparing the size of the structural resistance and the load effect. The condition that should be met for its safe operation is: Z = RS ≥ 0, where Z is the functional function of the structure, R is the resistance of the structure itself, and S is the external load effect.

7. The reliability analysis method of composite blades according to claim 6, characterized in that: In S4, the polynomial response surface method needs a lot of data to construct the performance function. According to the probability density function and cumulative distribution function of the three variables, three probability level points are extracted for each random variable, and then 13 sample points including the midpoints of the edges and the center points are selected, and the response values ​​of these sample points, i.e. the maximum strain value, are simulated and calculated.

8. The composite blade reliability analysis method according to claim 7, characterized in that: In S4, the method for constructing the blade structure function function is: applying the least squares method to fit and analyze the influence of three random variables on the response value, and obtaining the response surface function of the composite blade structure failure, that is, the blade structure function.

9. The composite blade reliability analysis method according to claim 1, characterized in that: In S5, the reliability of the composite blade is calculated by using the first-order second-moment method to calculate the constructed blade structural performance function.

10. The composite blade reliability analysis method according to claim 9, characterized in that: The principle of the first-order second moment method is to use the mean value and standard deviation of random variables to solve the reliability index β of the structure, and expand the limit state equation at the center point according to the Taylor series. in: β is the reliability index of the structure, Z is the structural performance function, μ is the mean value, σ is the standard deviation, and x i is the ith variable.

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