CN113435079A - Landing gear fatigue life analysis method based on finite element method - Google Patents
Landing gear fatigue life analysis method based on finite element method Download PDFInfo
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Abstract
The application provides a landing gear fatigue life analysis method based on a finite element method, which comprises the following steps: establishing a finite element model of the landing gear structure; extracting unit loads in XYZ directions and-X-Y-Z directions of a whole machine coordinate system and unit loads applied to a landing gear structure along the application direction of a retractable actuator of the landing gear from the axle center and the tire departure point of the finite element model, thereby obtaining 13 finite element unit stress calculation models of the axle center in six directions of XYZ and-X-Y-Z, the tire departure point in six directions of XYZ and-X-Y-Z and the retractable actuator in the application direction; applying each load point in the load spectrum to 13 finite element unit stress calculation models to obtain the stress of each load point, thereby obtaining a stress spectrum comprising a plurality of load points; and obtaining a stress spectrum of each section according to the method, calculating the damage of the undercarriage at each load point, and accumulating the damage of the undercarriage at each load point to obtain the total damage under the whole load spectrum, thereby obtaining the fatigue life of the undercarriage.
Description
Technical Field
The application belongs to the technical field of aircraft structural design, and particularly relates to a landing gear fatigue life analysis method based on a finite element method.
Background
The landing gear is an important bearing structure of the airplane, the landing gear of the early airplane is designed according to static strength, and the safety of the structure can be ensured as long as the static strength requirement is met and the static test requirement is met. With the continuous experience of practical use, it is recognized that static strength design alone is not sufficient, and failure of the landing gear is caused by fatigue, which occurs under alternating loads below the design load, with failure always starting locally. Early detection and determination of fatigue weakness is more important.
There are three main methods for estimating lifetime, of which the nominal stress method is most commonly used. The nominal stress method firstly determines the dangerous profile of the structure and then calculates the maximum stress of the modified profile. For simple parts, calculations can be made using conventional methods; for a complex structure and a stress concentration part, the condition that the load spectrum working condition of the undercarriage is more is often accompanied, so that a lot of troubles are brought to the service life estimation work, the stress concentration part needs to search a manual to obtain an empirical value, the comparison structure size does not need to be different in value, a lot of uncertainties exist, and the accuracy is to be verified.
In order to avoid unnecessary calculation work, reduce repetitive work, and improve accuracy, a method is needed that avoids the above problems, and can satisfy the requirement of life estimation and perform fast calculation for complex structures.
Disclosure of Invention
The present application aims to provide a landing gear fatigue life analysis method based on a finite element method to solve or mitigate at least one of the problems of the background art.
The technical scheme of the application is as follows: a landing gear fatigue life analysis method based on a finite element method comprises the following steps:
establishing a finite element model of the landing gear structure;
extracting unit loads in XYZ directions and-X-Y-Z directions of a whole machine coordinate system and unit loads applied to a landing gear structure along the application direction of a retractable actuator of the landing gear from the axle center and the tire departure point of the finite element model, thereby obtaining 13 finite element unit stress calculation models of the axle center in six directions of XYZ and-X-Y-Z, the tire departure point in six directions of XYZ and-X-Y-Z and the retractable actuator in the application direction;
applying each load point in the load spectrum to 13 finite element unit stress calculation models to obtain the stress of each load point, thereby obtaining a stress spectrum comprising a plurality of load points;
and obtaining a stress spectrum of each section according to the method, calculating the damage of the undercarriage at each load point, and accumulating the damage of the undercarriage at each load point to obtain the total damage under the whole load spectrum, thereby obtaining the fatigue life of the undercarriage.
Further, when a finite element model of the landing gear structure is established, if local position parameters and boundary loads of the landing gear structure can be obtained, establishing a finite element model of a single part or component in the landing gear structure; and if the local position parameters and the boundary load of the landing gear structure cannot be obtained, establishing an integral finite element model of the landing gear structure comprising parts or components.
Further, when the stress spectrum is obtained, when the load of a certain point in the load spectrum does not contain a certain finite element model load value in the stress calculation model of 13 finite element units, the load is multiplied by 0 to replace the load value.
Further, a certain load value in the load spectrum is:
wherein P, F are the load and force, the lower corner K represents the axle center position, L represents the tire ground contact position, zdt represents the actuator cylinder, and the upper corners x, y, z represent the coordinate system direction.
Further, the unit stress values of the 13 finite element unit stress calculation models are as follows:
in the formula, σ represents a unit stress.
Further, the damage of each load point calculated according to the stress spectrum of each section is obtained according to an S-N curve.
Further, the stress of a certain dangerous profile is:
where σ denotes stress, P, F denotes load and applied force, respectively, the lower corner K denotes the wheel axle center position, L denotes the tire ground contact point position, zdt denotes the actuator cylinder, and the upper corners x, y, and z denote the coordinate system directions.
The landing gear fatigue life analysis method based on the finite element method can improve the landing gear life analysis work on the premise of ensuring that the calculation result is relatively accurate, and is simple to operate, accurate and reliable.
Drawings
In order to more clearly illustrate the technical solutions provided by the present application, the following briefly introduces the accompanying drawings. It is to be expressly understood that the drawings described below are only illustrative of some embodiments of the invention.
FIG. 1 is a flowchart of a landing gear fatigue life analysis method based on a finite element method.
FIG. 2 is a four view landing gear finite element integral model established in an embodiment of the present application.
Detailed Description
In order to make the implementation objects, technical solutions and advantages of the present application clearer, the technical solutions in the embodiments of the present application will be described in more detail below with reference to the drawings in the embodiments of the present application.
In order to realize the rapid estimation of the fatigue life of the undercarriage structure and to improve the undercarriage in an iterative manner more quickly, the application provides an undercarriage fatigue life analysis method based on a finite element method.
As shown in fig. 1, the landing gear fatigue life analysis method based on the finite element method provided by the present application includes:
s1, establishing a finite element model of the landing gear
In the present application, if the local position and boundary load are known, the model of a single part can be established at the component level; for parts which cannot know or cannot quickly give boundary load, an integral landing gear finite element model is built and calculated.
By analyzing the landing gear load, the main external input loads to the landing gear are the ground load at the tire/wheel center and the tension and compression load of the retractable actuator, and these loads are transmitted to the constraint point (body) through the landing gear. The inner part of the landing gear is formed by combining an air cavity and an oil cavity, so that the piston rod and the outer cylinder of the landing gear have non-contact force in the axial direction of the landing gear.
According to the landing gear load, the ground load acts on a wheel center/tire grounding point, the load in the XZ direction is transmitted to the contact point of the outer cylinder and the piston rod from the tire/wheel center in the form of a simple support beam through the contact of the piston rod and the outer cylinder, and is transmitted to the machine body through the outer cylinder, wherein the contact part of the outer cylinder and the piston rod is considered not to transmit bending moment. The Y-direction load is mainly transmitted to the outer cylinder from the lower flange of the piston rod through the air spring, and finally transmitted to the machine body through the outer cylinder.
A finite element integral model of the landing gear built by the above analysis is shown in figure 2.
S2, extracting the part stress under unit load from the finite element result
Since the landing gear structure is not a symmetrical structure, the following considerations are made in modeling:
and respectively establishing X, Y, Z directional (full-machine coordinate system) unit load models, including three directional load models at different loading positions. For the landing gear, 12 finite element unit stress calculation models in total are established for unit loads in X, Y, Z three directions and-X-Y-Z three directions acting at two positions of a wheel center and a tire grounding point. In addition, the load of the landing gear retraction actuator cylinder is also considered, namely a finite element unit calculation model under the unit load is also established.
And then extracting the unit stress of the dangerous part in the 13 finite element unit stress calculation models.
S3, converting the calculation result in the step S2 into a corresponding stress spectrum according to the load spectrum
And multiplying the unit stress of the dangerous part in the 13 finite element unit stress calculation models by each load value of the load spectrum to obtain the stress under the load, thereby obtaining the stress spectrum.
In the case of creating the stress spectrum, if the load at each point in the load spectrum does not include any model load value in the stress calculation model of 13 finite element elements, the load is multiplied by 0 instead.
A certain load value in the load spectrum is:
wherein P, F are the load and force, the lower corner K represents the axle center position, L represents the tire ground contact position, zdt represents the actuator cylinder, and the upper corners x, y, z represent the coordinate system direction.
The unit stress values in the 13 finite element unit stress calculation models are as follows:
the stress for a certain hazardous profile is then:
σ represents stress, and the corner marks are as defined above.
The load spectrum in an embodiment of the present application is shown in table 1.
Table 1 load spectrum example
The stress spectrum obtained from the above load spectrum is shown in table 2.
Table 2 stress spectra example
S4 nominal stress method life analysis
Calculating the damage of the landing gear structure at the load point according to the load stress in the load spectrum, accumulating the damage of the load point to obtain the total damage under the whole load spectrum, and further obtaining the fatigue life of the landing gear
According to the method, stress spectrums of all the sections are calculated, damage of the landing gear under all the load points can be calculated according to S-N curves of the materials, total damage of the dangerous sections is obtained by accumulating loss of the landing gear under all the load points, and finally a service life analysis result is obtained, wherein the total damage and the service life of the landing gear obtained under the embodiment are shown in a table 3.
Table 3 damage and life examples
The invention provides a landing gear fatigue life analysis method based on a finite element method, which ensures that the landing gear life analysis work is rapidly carried out and the result is accurately calculated. The method provides reference for the service life analysis work of the subsequent model landing gear, and the calculation method is simple to operate, accurate and reliable.
The above description is only for the specific embodiments of the present application, but the scope of the present application is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present application should be covered within the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.
Claims (7)
1. A landing gear fatigue life analysis method based on a finite element method is characterized by comprising the following steps:
establishing a finite element model of the landing gear structure;
extracting unit loads in XYZ directions and-X-Y-Z directions of a whole machine coordinate system and unit loads applied to a landing gear structure along the application direction of a retractable actuator of the landing gear from the axle center and the tire departure point of the finite element model, thereby obtaining 13 finite element unit stress calculation models of the axle center in six directions of XYZ and-X-Y-Z, the tire departure point in six directions of XYZ and-X-Y-Z and the retractable actuator in the application direction;
applying each load point in the load spectrum to 13 finite element unit stress calculation models to obtain the stress of each load point, thereby obtaining a stress spectrum comprising a plurality of load points;
and obtaining a stress spectrum of each section according to the method, calculating the damage of the undercarriage at each load point, and accumulating the damage of the undercarriage at each load point to obtain the total damage under the whole load spectrum, thereby obtaining the fatigue life of the undercarriage.
2. A landing gear fatigue life analysis method based on a finite element method according to claim 1, wherein when the finite element model of the landing gear structure is established, if the local position parameters and the boundary load of the landing gear structure can be obtained, the finite element model of the single part or the component in the landing gear structure is established; and if the local position parameters and the boundary load of the landing gear structure cannot be obtained, establishing an integral finite element model of the landing gear structure comprising parts or components.
3. A method for analyzing fatigue life of landing gear based on finite element method according to claim 1, wherein when obtaining the stress spectrum, when the load at a certain point in the load spectrum does not contain a certain finite element model load value in the stress calculation model of 13 finite element units, the stress spectrum is multiplied by 0 instead.
4. The finite element method-based landing gear fatigue life analysis method according to claim 1, wherein a certain load value in the load spectrum is:
wherein P, F are the load and force, the lower corner K represents the axle center position, L represents the tire ground contact position, zdt represents the actuator cylinder, and the upper corners x, y, z represent the coordinate system direction.
5. A landing gear fatigue life analysis method based on finite element method according to claim 4, characterized in that the unit stress values of 13 finite element unit stress calculation models are:
in the formula, σ represents a unit stress.
6. A landing gear fatigue life analysis method based on a finite element method according to claim 1, wherein the damage of each load point calculated from the stress spectrum of each section is obtained from an S-N curve.
7. A landing gear fatigue life analysis method based on a finite element method according to claim 6, wherein the stress of a certain dangerous section is:
where σ denotes stress, P, F denotes load and applied force, respectively, the lower corner K denotes the wheel axle center position, L denotes the tire ground contact point position, zdt denotes the actuator cylinder, and the upper corners x, y, and z denote the coordinate system directions.
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Cited By (3)
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| CN114235448A (en) * | 2021-12-08 | 2022-03-25 | 中车青岛四方机车车辆股份有限公司 | Rail vehicle bogie wheel fatigue damage assessment method and system |
| CN114329768A (en) * | 2021-12-06 | 2022-04-12 | 中航飞机起落架有限责任公司 | Method, system, equipment and storage medium for calculating fatigue stress of undercarriage |
| CN114235448B (en) * | 2021-12-08 | 2024-07-12 | 中车青岛四方机车车辆股份有限公司 | Rail vehicle bogie wheel fatigue damage assessment method and system |
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN114329768A (en) * | 2021-12-06 | 2022-04-12 | 中航飞机起落架有限责任公司 | Method, system, equipment and storage medium for calculating fatigue stress of undercarriage |
| CN114329768B (en) * | 2021-12-06 | 2024-05-07 | 中航飞机起落架有限责任公司 | Landing gear fatigue stress calculation method, system, equipment and storage medium |
| CN114235448A (en) * | 2021-12-08 | 2022-03-25 | 中车青岛四方机车车辆股份有限公司 | Rail vehicle bogie wheel fatigue damage assessment method and system |
| CN114235448B (en) * | 2021-12-08 | 2024-07-12 | 中车青岛四方机车车辆股份有限公司 | Rail vehicle bogie wheel fatigue damage assessment method and system |
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