A method for analyzing vibration fatigue of an aircraft structure

Abstract

This application belongs to the field of aircraft structural vibration fatigue design technology, specifically involving an aircraft structural vibration fatigue analysis method that considers the influence of static stress on vibration fatigue damage, making the vibration fatigue life analysis more accurate. It can accurately guide the design of aircraft structural vibration fatigue life and avoid the problems of inaccurate vibration fatigue life analysis, which leads to insufficient actual structural vibration fatigue life or overweight structural design.

Description

Technical Field

[0001] This application belongs to the field of aircraft structural vibration fatigue design technology, specifically relating to an aircraft structural vibration fatigue analysis method. Background Technology

[0002] During aircraft flight, structures such as the fuselage and wings are subjected to not only cyclic vibration stress caused by vibration, but also static stress caused by flight static loads. Structural vibration fatigue damage is fatigue damage caused by the superposition of cyclic vibration stress on top of static stress.

[0003] In current aircraft structural vibration fatigue design, vibration fatigue analysis typically only considers fatigue damage caused by cyclic vibration stress, neglecting the impact of static stress caused by flight static loads on vibration fatigue life. Using this method for vibration fatigue life analysis results in a larger-than-actual vibration fatigue life when the static stress in the structure is tensile, leading to insufficient vibration fatigue life for the aircraft structure. Conversely, when the static stress in the structure is compressive, the vibration fatigue analysis results are smaller than the actual vibration fatigue life, resulting in overweight aircraft structural designs.

[0004] In view of the aforementioned technical deficiencies, this application is hereby filed. Summary of the Invention

[0005] The purpose of this application is to address the problem that current vibration fatigue life analysis does not consider the static stress caused by flight static loads, resulting in inaccurate vibration fatigue life analysis, which leads to insufficient actual structural vibration fatigue life or excessive structural design weight. This application provides a vibration fatigue analysis method for aircraft structures that considers the influence of static stress to improve the accuracy of vibration fatigue analysis.

[0006] The technical solution of this application is:

[0007] A method for vibration fatigue analysis of aircraft structures includes:

[0008] Step 1: Obtain the static stress of the aircraft structure ;

[0009] Step 2: Static stress based on aircraft structure The SN curve of material fatigue in the double logarithmic coordinate system is corrected;

[0010] Step 3: Calculate the characteristic parameters of the corrected material based on the modified SN curve in the double logarithmic coordinate system for material fatigue. :

[0011] ;

[0012] in,

[0013] This is the negative reciprocal of the slope of the modified material fatigue SN curve in a double logarithmic coordinate system.

[0014] To correct the stress level of the material, This represents the number of stress cycles.

[0015] Step 4: Obtain the vibration stress power spectral density function of the aircraft structure. ;

[0016] Step 5: Vibration stress power spectral density function based on aircraft structure Calculate the power spectral density of vibration stress Step Moment ;

[0017] Step Six: Vibration Stress Power Spectral Density Based on Aircraft Structure Step Moment Calculate intermediate parameters , , , , , :

[0018] , ;

[0019] , , ;

[0020] , ; ;

[0021] in, , For process parameters;

[0022] Step 7: Calculate the fatigue damage caused by continuous stress in the aircraft structure. :

[0023] ;

[0024] in, This represents the upper limit of the integral stress level.

[0025] Step 8: Calculate the vibration fatigue life of the aircraft structure. :

[0026] .

[0027] According to at least one embodiment of this application, in the above-described aircraft structural vibration fatigue analysis method, in step one, the static stress of the part of interest in the aircraft structure is obtained through static strength simulation analysis. .

[0028] According to at least one embodiment of this application, in the above-described aircraft structural vibration fatigue analysis method, in step one, the static stress of the part of interest in the aircraft structure is obtained through structural static stress testing. .

[0029] According to at least one embodiment of this application, in the above-described aircraft structure vibration fatigue analysis method, in step two, the SN curve of the material fatigue in a double logarithmic coordinate system is obtained by consulting a material handbook.

[0030] According to at least one embodiment of this application, in the above-described method for analyzing the vibration fatigue of aircraft structures, in step two, the SN curve of material fatigue in a double logarithmic coordinate system is obtained based on the analysis of experimental results.

[0031] According to at least one embodiment of this application, in the above-described aircraft structural vibration fatigue analysis method, step two specifically comprises:

[0032] calculate: ;

[0033] in, The stress level is the adjusted infinite life fatigue limit of the material.

[0034] The stress level represents the fatigue limit of a material's infinite lifespan.

[0035] The ultimate strength of the material;

[0036] In the material fatigue double logarithmic coordinate system, through At the given point, draw a line parallel to the SN curve to correct the SN curve.

[0037] According to at least one embodiment of this application, in the above-described aircraft structural vibration fatigue analysis method, in step two, the stress cycle number is used as the basis for the measurement. As the conditional fatigue limit, the corresponding stress level is taken as... .

[0038] According to at least one embodiment of this application, in the above-described aircraft structural vibration fatigue analysis method, step five specifically comprises:

[0039] .

[0040] According to at least one embodiment of this application, in the above-described aircraft structural vibration fatigue analysis method, step five involves calculating the vibration stress power spectral density. Step Moment Up to level 4.

[0041] According to at least one embodiment of this application, in the above-described aircraft structural vibration fatigue analysis method, step seven includes:

[0042] . Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the aircraft structural vibration fatigue analysis method provided in the embodiments of this application;

[0044] Figure 2 This is a schematic diagram illustrating the correction of the SN curve in a double logarithmic coordinate system for material fatigue, provided in an embodiment of this application.

[0045] Figure 3 This is a schematic diagram of the vibration stress power spectral density function of an aircraft structure provided in an embodiment of this application;

[0046] Figure 4 This is a schematic diagram of the probability density function of vibration stress amplitude provided in the embodiments of this application.

[0047] To better illustrate this embodiment, some content in the accompanying drawings may be omitted. They are for illustrative purposes only and should not be construed as limiting the scope of this application. Detailed Implementation

[0048] To make the technical solution and advantages of this application clearer, the technical solution of this application will be described in a clearer and more complete manner below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only some embodiments of this application, and are only used to explain this application, not to limit this application. It should be noted that, for ease of description, only the parts related to this application are shown in the accompanying drawings, and other related parts can be referred to the general design.

[0049] Furthermore, unless otherwise defined, the technical or scientific terms used in this application description shall have the ordinary meaning understood by one of ordinary skill in the art to which this application pertains. The word "comprising" as used in this application description indicates that the concept preceding the word encompasses the concepts listed following the word and their equivalents, without excluding other related concepts.

[0050] A method for analyzing the vibration fatigue of aircraft structures, considering the influence of static stress on vibration fatigue life, such as... Figure 1 As shown.

[0051] Step 1: Obtain the static stress of the aircraft structure .

[0052] Static stress at key parts of the aircraft structure can be obtained through static strength simulation analysis or structural static stress testing. .

[0053] Step 2: Static stress based on aircraft structure The SN curve of material fatigue in a double logarithmic coordinate system is corrected.

[0054] The fatigue SN curve in a double logarithmic coordinate system for materials, obtained by consulting material handbooks or analyzing experimental results, includes:

[0055] ……………(1)

[0056] in, , This is called the material constant. This is the negative reciprocal of the slope of the SN curve in the double logarithmic coordinate system for material fatigue. These are the characteristic parameters of the material;

[0057] The stress level of the material, The number of stress cycles is denoted as .

[0058] ……………(2)

[0059] in, The stress level is the adjusted infinite life fatigue limit of the material.

[0060] The stress level represents the fatigue limit of a material's infinite life. For SN curves without a clear fatigue limit, the number of stress cycles can be used. As the conditional fatigue limit, the corresponding stress level is selected;

[0061] This represents the material's strength limit.

[0062] In the material fatigue double logarithmic coordinate system, through At the given point, draw a line parallel to the SN curve to correct the SN curve.

[0063] Step 3: Calculate the characteristic parameters of the corrected material based on the modified SN curve in the double logarithmic coordinate system for material fatigue. :

[0064] ……………(3)

[0065] in,

[0066] This is the negative reciprocal of the slope of the modified material fatigue SN curve in a double logarithmic coordinate system.

[0067] To correct the stress level of the material, The number of stress cycles is denoted as .

[0068] Step 4: Obtain the vibration stress power spectral density function of the aircraft structure. .

[0069] Establish a finite element model of aircraft structural dynamics to perform stochastic vibration response analysis, or conduct structural vibration stress tests to obtain the vibration stress power spectral density function. It is possible to obtain only the vibration stress power spectral density function of the part of interest. Vibration stress power spectral density function It is the vibration frequency The corresponding one-sided stress power spectral density.

[0070] Step 5: Vibration stress power spectral density function based on aircraft structure Calculate the power spectral density of vibration stress Step Moment Typically, calculations are performed up to the 4th order.

[0071] ……………(4)

[0072] Step Six: Vibration Stress Power Spectral Density Based on Aircraft Structure Step Moment Calculate intermediate parameters , , , , :

[0073] ……………(5)

[0074] ……………(6)

[0075] ……………(7)

[0076] ……………(8)

[0077] ……………(9)

[0078] ……………(10)

[0079] ……………(11)

[0080] ……………(12)

[0081] in, , , For process parameters, Specifically, it is the expected value of the number of stress amplitudes per unit time, expressed in the form of moments of the stress power spectral density.

[0082] The probability density function of vibration stress amplitude can be further constructed:

[0083] ……………(13)

[0084] ……………(14)

[0085] in, This is an intermediate parameter.

[0086] Step 7: Calculate the fatigue damage caused by continuous stress in the aircraft structure. :

[0087] ……………(15)

[0088] in, This represents the upper limit of the integral stress level for broadband random vibration. Take 3 times the 0th moment of the vibration stress power spectral density, that is .

[0089] Step 8: Calculate the vibration fatigue life of the aircraft structure. :

[0090] ……………(15)

[0091] Calculated vibration fatigue life of aircraft structure The unit is seconds (s). To calculate flight hours, divide by 3600.

[0092] In a specific example, the aircraft structural vibration fatigue analysis method disclosed in the above embodiments is implemented as follows:

[0093] Step 1: Obtain the static stress of the relevant parts of the aircraft structure through static strength simulation analysis. It is 134 MPa.

[0094] Step 2: Consult the material handbook to obtain the SN curve of material fatigue in a double logarithmic coordinate system. We have:

[0095] ;

[0096] in, , .

[0097] Pick ,calculate Correction of the SN curve of material fatigue in a double logarithmic coordinate system

[0098] Step 3: Calculate the characteristic parameters of the corrected material. :

[0099] ;

[0100] in, , .

[0101] Step 4: Perform random vibration response analysis to obtain the vibration stress power spectral density function of the aircraft structure. ,like Figure 3 As shown.

[0102] Step 5: Calculate the power spectral density of vibration stress. Step Moment :

[0103] ;

[0104] have, , , , .

[0105] Step Six: Calculation , , ;

[0106] , , , , .

[0107] Construct the probability density function of vibration stress amplitude, such as Figure 4 As shown:

[0108] .

[0109] Step 7: Calculate the fatigue damage caused by continuous stress in the aircraft structure. :

[0110] .

[0111] Step 8: Calculate the vibration fatigue life of the aircraft structure. :

[0112] The total flight hours were 1851.

[0113] The aircraft structure vibration fatigue analysis method disclosed in the above embodiments considers the influence of static stress on vibration fatigue damage, making the vibration fatigue life analysis more accurate. It can accurately guide the design of aircraft structure vibration fatigue life, optimize the aircraft structure, enable the aircraft structure to meet the design requirements of the entire aircraft life, and take into account the vibration reduction design of the aircraft structure to reduce maintenance costs.

[0114] The technical solution of this application has been described in conjunction with the preferred embodiments shown in the accompanying drawings. Those skilled in the art should understand that the scope of protection of this application is obviously not limited to these specific embodiments. Without departing from the principles of this application, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of this application.

Claims

1. A method for analyzing the vibration fatigue of aircraft structures, characterized in that, include: Step 1: Obtain the static stress of the aircraft structure ; Step 2: Static stress based on aircraft structure The SN curve of material fatigue in the double logarithmic coordinate system is corrected; Step 3: Calculate the characteristic parameters of the corrected material based on the modified SN curve in the double logarithmic coordinate system for material fatigue. : ； in, This is the negative reciprocal of the slope of the modified material fatigue SN curve in a double logarithmic coordinate system. To correct the stress level of the material, This represents the number of stress cycles. Step 4: Obtain the vibration stress power spectral density function of the aircraft structure. ; Step 5: Vibration stress power spectral density function based on aircraft structure Calculate the power spectral density of vibration stress Step Moment ; Step Six: Vibration Stress Power Spectral Density Based on Aircraft Structure Step Moment Calculate intermediate parameters , , , , , : ， ； ， ， ； ， ； ； in, , For process parameters; Step 7: Calculate the fatigue damage caused by continuous stress in the aircraft structure. : ； in, This represents the upper limit of the integral stress level. Step 8: Calculate the vibration fatigue life of the aircraft structure. : 。 2. The method for analyzing the vibration fatigue of aircraft structures according to claim 1, characterized in that, In step one, static stress of the relevant parts of the aircraft structure is obtained through static strength simulation analysis. .

3. The method for analyzing the vibration fatigue of aircraft structures according to claim 1, characterized in that, In step one, static stress of the relevant parts of the aircraft structure is obtained through structural static stress testing. .

4. The method for analyzing the vibration fatigue of aircraft structures according to claim 1, characterized in that, In step two, the SN curve of material fatigue in a double logarithmic coordinate system is obtained by consulting the material handbook.

5. The method for analyzing the vibration fatigue of aircraft structures according to claim 4, characterized in that, In step two, based on the analysis of the experimental results, the SN curve of material fatigue in a double logarithmic coordinate system is obtained.

6. The method for analyzing the vibration fatigue of aircraft structures according to claim 5, characterized in that, Step two is as follows: calculate: ; in, The stress level is the adjusted infinite life fatigue limit of the material. The stress level represents the fatigue limit of a material's infinite lifespan. The ultimate strength of the material; In the material fatigue double logarithmic coordinate system, through At the given point, draw a line parallel to the SN curve to correct the SN curve.

7. The method for analyzing the vibration fatigue of aircraft structures according to claim 6, characterized in that, In step two, the number of stress cycles is used as the basis for calculation. As the conditional fatigue limit, the corresponding stress level is taken as... .

8. The method for analyzing the vibration fatigue of aircraft structures according to claim 7, characterized in that, Step five is as follows: 。 9. The method for analyzing the vibration fatigue of aircraft structures according to claim 8, characterized in that, In step five, the vibration stress power spectral density is calculated. Step Moment Up to level 4.

10. The method for analyzing the vibration fatigue of aircraft structures according to claim 9, characterized in that, In step seven: 。

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