Method for calculating local stress of aircraft structure web opening based on overall finite element model

Abstract

The application discloses a kind of based on overall finite element model's aircraft structure web opening local stress calculation method, based on the stress analysis result of overall finite element model extraction gross section reference stress;According to the stress concentration coefficient of opening geometric size and web unit stress state;Based on the section stiffness loss caused by opening and the compensation of section stiffness by boss, introduce opening load reduction coefficient, finally determine the local stress of web hole edge.This application can quickly determine the local detail stress of various web openings of aircraft structure, so as to carry out structural strength design.

Description

Technical Field

[0001] This invention belongs to the field of aircraft structural strength, specifically relating to a method for calculating local stress in the web openings of aircraft structures based on a global finite element model. Background Technology

[0002] Web perforations are among the most widespread, important, and typical structural details in aircraft structures. During aircraft design and development, detailed stress analysis is typically used to obtain the local stress at the edge of web perforations. However, this method is complex and requires significant computational and human resources, hindering rapid iteration in aircraft structural design. Summary of the Invention

[0003] The purpose of this invention is to provide a method for calculating local stress in the web openings of aircraft structures based on a global finite element model. This invention can quickly determine the local detailed stresses of various web openings in aircraft structures, facilitating structural strength design.

[0004] The technical solution is as follows: A method for calculating local stress of openings in the web of an aircraft structure based on a global finite element model. The method extracts the reference stress of the gross section based on the stress analysis results of the global finite element model; determines the stress concentration factor based on the opening geometry and the stress state of the web element; and introduces the opening load reduction factor based on the section stiffness loss caused by the opening and the compensation of the boss on the section stiffness, and finally determines the local stress at the edge of the web opening.

[0005] In the aforementioned method for calculating local stress at the web opening of an aircraft structure based on a global finite element model, the local stress at the edge of the web opening is calculated using the following formula:

[0006] σ max =σ ref *K t *(1-β loss (1)

[0007] Where, σ max For the local stress at the edge of the hole, σ ref K represents the reference stress of the gross section. t β is the stress concentration factor. loss This is the reduction factor for the load on the opening.

[0008] The aforementioned method for calculating local stress in the web openings of aircraft structures based on a global finite element model includes the following steps:

[0009] S1. For the web hole being analyzed, determine the reference stress σ of the gross section based on the stress state of the corresponding web element in the overall finite element model. ref ;;

[0010] S2. For the web hole mentioned in step S1, based on the hole geometry and web element stress state, and taking the stress concentration factor of a uniaxial infinitely wide plate hole as a benchmark, and considering finite width correction, hole shape correction, biaxial stress correction, and boss correction, calculate the stress concentration factor K. t ;

[0011] S3. For the web hole mentioned in step S1, calculate the opening load reduction factor according to the actual web hole structure size;

[0012] S4. Substitute the parameters determined in steps S1 to S3 into equation (1) to determine the local stress at the edge of the target web hole.

[0013] In the aforementioned method for calculating local stress of openings in the web of an aircraft structure based on a global finite element model, in step S1, if the opening is located in the middle region of the web, the principal stress of the web element is used as the reference stress of the web opening cross section.

[0014] In the aforementioned method for calculating local stress of openings in the web of an aircraft structure based on a global finite element model, in step S1, if the opening is located in the edge region of the web, the principal stress of the nearest node is used as the reference stress of the web opening section.

[0015] In the aforementioned method for calculating local stress in the web openings of aircraft structures based on a global finite element model, in step S2, the stress concentration factor K... t The calculation method is as follows:

[0016] K t =β pad *(K t0 *β w *β elip *β bi -1)+1

[0017] In the formula, K t0 β is the reference stress concentration factor for a uniaxial infinitely wide plate cavity; w β is the finite width correction factor; elip β is the hole shape correction factor; bi β is the biaxial stress correction factor; pad This is the correction factor for the boss.

[0018] In the aforementioned method for calculating local stress in the web opening of an aircraft structure based on a global finite element model, if the target web opening is a single hole, then K t0 =3.0; if the target web hole is porous, then K t0 Consult the Stress Concentration Handbook for details.

[0019] In the aforementioned method for calculating local stress in the web openings of aircraft structures based on the overall finite element model, β w Calculate using the following formula:

[0020] β w =1.0 (e / d>2)

[0021] β w =1.1 (e / d≤2)

[0022] Where e is the distance from the web hole to the frame / beam edge strip in the direction of maximum principal stress, and d is the diameter of the web hole.

[0023] In the aforementioned method for calculating local stress in the web openings of aircraft structures based on the overall finite element model, β bi Calculate using the following formula:

[0024] β bi =1-σ2 / σ1 / 3

[0025] Where σ1 and σ2 are the maximum and minimum principal stresses in the plane of the corresponding web element in the overall finite element model, respectively.

[0026] In the aforementioned method for calculating local stress in the web opening of an aircraft structure based on a global finite element model, if it is a single-sided boss, β pad =1.1, if it is a double-sided boss, β pad Obtained by consulting the Stress Concentration Handbook.

[0027] In the aforementioned method for calculating local stress in the web openings of aircraft structures based on the overall finite element model, β loss Calculate using the following formula:

[0028] If d / W < 0.45, then β loss =0;

[0029] If d / W ≥ 0.45, then β loss =0.6*d / W*β pad ;

[0030] Where d is the diameter of the web hole, W is the target web grid width perpendicular to the direction of maximum principal stress, and β pad This is the correction factor for the boss.

[0031] Beneficial effects: Web openings are one of the most widespread, important, and typical structural details in aircraft structures, often leading to fatigue cracks due to stress concentration. This invention, based on the analysis results of the overall finite element model of the aircraft structure, can quickly calculate the local stress at the edge of the web opening. It comprehensively considers the influence of factors such as the geometric dimensions of the web opening, the plane stress state, and the reduction of the opening load, ensuring the accuracy of the calculation results and avoiding the complex detailed stress analysis in the calculation process. This significantly improves the efficiency of fatigue strength analysis of web openings in aircraft structures, thereby enabling rapid iterative optimization design of aircraft structural details and durability analysis covering the entire load-bearing structure of the aircraft. Attached Figure Description

[0032] Figure 1 This is the technical process of the present invention;

[0033] Figure 2 The target web hole in the example;

[0034] Figure 3 The following are the principal stress cloud diagrams of the overall finite element model corresponding to the target web hole in the example; where (a) is the maximum principal stress cloud diagram of the plate element and (b) is the minimum principal stress cloud diagram of the plate element. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0036] Example 1. A method for calculating local stress in the web opening of an aircraft structure based on a global finite element model, see [link to example]. Figures 1-3 Taking the web hole near the frame flange of a certain type of aircraft as an example (see...) Figure 2 This document describes a method for calculating local stress in the web openings of aircraft structures, including the following steps:

[0037] 1) For this web hole, determine the reference stress σ of the gross section based on the stress state of the corresponding web element in the overall finite element model. ref ;

[0038] In the overall finite element model, the maximum and minimum principal stresses in the plane of the plate element corresponding to the web hole are as follows: Figure 3 As shown, the web hole is located in the middle region of the web. The principal stresses of the web elements are used as the reference stresses for the gross cross-section of the web hole. The maximum principal stress σ1 = 232 MPa, the minimum principal stress σ2 = -125 MPa, and the reference stress σ... ref =232MPa.

[0039] 2) Based on the web hole size parameters, calculate various correction factors and determine the stress concentration factor K. t ;

[0040] The web hole is a single hole, and the reference stress concentration factor K is... t0 =3.0;

[0041] The edge distance of the web hole is e = 70 mm, the hole diameter is d = 43 mm, and the finite width correction factor is β. w =1.1 (e / d<2);

[0042] The web hole is an oblong-elliptical hole. Based on the actual structural dimensions, the hole shape correction factor β was calculated by consulting a stress concentration factor handbook. elip =0.84;

[0043] The maximum principal stress of the web hole is σ1 = 232 MPa, the minimum principal stress is σ2 = -125 MPa, and the biaxial stress correction factor is β. bi =1 - (-125 / 232 / 3) = 1.18;

[0044] The web hole is a double-sided reinforced boss. Based on the actual structural dimensions, the boss correction factor β was calculated by consulting the stress concentration factor handbook. pad =0.62.

[0045] Stress concentration factor K t =0.62*(3.0*1.1*0.84*1.18-1)+1=2.41

[0046] 3) Calculate the opening load reduction factor based on the web hole size parameters;

[0047] The diameter of the web hole is d = 43 mm, the width of the web grid is W = 140 mm, and the opening load reduction factor is β. loss =0 (d / W<0.45);

[0048] 4) Substitute the parameters determined in the above steps into the local stress calculation formula to determine the local stress at the edge of the hole in the web.

[0049] σ max =σ ref *K t *(1-β loss )=232*2.41*(1-0)=559MPa.

[0050] Example 2. A method for calculating local stress in the web opening of an aircraft structure based on a global finite element model, see [link to example]. Figure 1 The present invention first extracts the reference stress of the gross section based on the stress analysis results of the overall finite element model; then determines the stress concentration factor according to the opening geometry and the stress state of the web elements; simultaneously, considering the actual loss of cross-sectional stiffness caused by the opening and the compensation of cross-sectional stiffness by the boss, an opening load reduction factor is introduced, thereby quickly determining the local stress at the edge of the web opening. The formula for calculating the local stress at the edge of the web opening is as follows:

[0051] σ max =σ ref *K t *(1-β loss )

[0052] Where, σmax For the local stress at the edge of the hole, σ ref K represents the reference stress of the gross section. t β is the stress concentration factor. loss The term "opening load reduction factor" refers to the local linear elastic stress mentioned in this invention.

[0053] The calculation steps are as follows:

[0054] S1: For the specific target web hole being analyzed, determine the reference stress σ of the gross section based on the stress state of the corresponding web element in the overall finite element model. ref ;

[0055] In step S1, it is necessary to determine the maximum principal stress σ1 and minimum principal stress σ2 of the corresponding web element in the overall finite element model.

[0056] In step S1, if the opening is located in the middle region of the web, the principal stress of the web element is used as the reference stress of the web hole cross section.

[0057] In step S1, if the opening is located in the edge region of the web, the principal stress of the nearest node is used as the reference stress of the web opening section.

[0058] S2: Regarding the web hole mentioned in S1, based on the hole geometry and the stress state of the web element, and taking the stress concentration factor of a uniaxial infinitely wide plate hole as a benchmark, considering finite width correction, hole shape correction, biaxial stress correction, and boss correction, the stress concentration factor K is calculated. t ;

[0059] In step S2, the stress concentration factor K t The calculation method is as follows:

[0060] K t =β pad *(K t0 *β w *β elip *β bi -1)+1

[0061] K t0 K is the reference stress concentration factor for a uniaxial infinitely wide plate hole. If the target web hole is a single hole, then K t0 The value is 3.0; if the target web hole is porous, then K t0 The stress concentration is related to factors such as the number of holes, hole diameter, and relative position. You can consult relevant stress concentration manuals for more information.

[0062] β w This is a finite-width correction factor, representing the effect of a finite-width plate on local stress, which can be determined based on relevant engineering experience.

[0063] β w =1.0 (e / d>2)

[0064] β w =1.1 (e / d≤2)

[0065] Where e is the distance from the web hole to the frame / beam edge strip in the direction of maximum principal stress, and d is the diameter of the web hole.

[0066] β elip This is the hole shape correction factor, which represents the influence of the hole shape (which can be divided into round hole, elliptical hole, oblong hole and square hole) on local stress. It can be obtained from relevant stress concentration manuals.

[0067] β bi This is a biaxial stress correction factor, representing the influence of the stress state of the web element on the local stress. The calculation method is as follows:

[0068] β bi =1-σ2 / σ1 / 3

[0069] Wherein, σ1 and σ2 are the maximum principal stress and minimum principal stress in the plane as described in S1, respectively.

[0070] β pad β is the boss correction factor, representing the effect of the reinforcing boss of the web hole on local stress. It is related to the size of the boss and the system holes. If it is a single-sided boss, due to the additional bending effect, β pad The value is 1.1. If it is a double-sided boss, β pad The value can be obtained from relevant stress concentration manuals.

[0071] S3: For the web hole mentioned in S1, calculate the opening load reduction factor based on the actual web hole structure size;

[0072] In step S3, since the web elements of the overall finite element model typically do not represent openings, the opening load reduction factor β is used. loss To characterize the loss of cross-sectional stiffness caused by the opening and the compensation of cross-sectional stiffness by the boss, the calculation method is as follows:

[0073] (1) If d / W < 0.45, then β loss =0;

[0074] (2) If d / W ≥ 0.45, then β loss =0.6*d / W*β pad ;

[0075] Where d is the diameter of the web hole, W is the target web grid width perpendicular to the direction of maximum principal stress, and β pad This is the boss correction coefficient described in S2.

[0076] S4: Substitute the parameters determined in steps S1 to S3 into the following calculation formula to determine the local stress at the edge of the target web hole;

[0077] σ max =σ ref *K t *(1-β loss ).

[0078] The above description is merely a specific embodiment of the present invention, providing a detailed description of the invention. Parts not covered herein are conventional techniques. However, the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. The scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for calculating local stress in the web opening of an aircraft structure based on a global finite element model, characterized in that, The reference stress of the gross section is extracted based on the stress analysis results of the overall finite element model; The stress concentration factor is determined based on the opening geometry and the stress state of the web element. Based on the loss of cross-sectional stiffness caused by the opening and the compensation of cross-sectional stiffness by the boss, the opening load reduction coefficient is introduced to finally determine the local stress at the edge of the web hole. Local stress at the edge of the web hole is calculated using the following formula: (1) Where, σ max For local stress at the edge of the hole, σ ref K represents the reference stress of the gross section. t β is the stress concentration factor. loss This is the reduction factor for the opening load; Includes the following steps: S1. For the web hole being analyzed, determine the reference stress σ of the gross section based on the stress state of the corresponding web element in the overall finite element model. ref ; S2. For the web hole mentioned in step S1, based on the hole geometry and web element stress state, and taking the stress concentration factor of a uniaxial infinitely wide plate hole as a benchmark, and considering finite width correction, hole shape correction, biaxial stress correction, and boss correction, calculate the stress concentration factor K. t ; S3. For the web hole mentioned in step S1, calculate the opening load reduction factor according to the actual web hole structure size; S4. Substitute the parameters determined in steps S1 to S3 into equation (1) to determine the local stress at the edge of the target web hole.

2. The method for calculating local stress in the web opening of an aircraft structure based on a global finite element model according to claim 1, characterized in that, In step S1, if the opening is located in the middle region of the web, the principal stress of the web element is used as the reference stress of the web opening cross section.

3. The method for calculating local stress in the web opening of an aircraft structure based on a global finite element model according to claim 1, characterized in that, In step S1, if the opening is located in the edge region of the web, the principal stress of the nearest node is used as the reference stress of the web opening section.

4. The method for calculating local stress in the web opening of an aircraft structure based on a global finite element model according to claim 1, characterized in that, In step S2, the stress concentration factor K t The calculation method is as follows: In the formula, K t0 β is the reference stress concentration factor for a uniaxial infinitely wide plate cavity; w This is a finite width correction factor; β elip This is the hole shape correction factor; β bi This is the biaxial stress correction factor; β pad This is the correction factor for the boss.

5. The method for calculating local stress in the web opening of an aircraft structure based on a global finite element model according to claim 4, characterized in that, If the target web hole is a single hole, then K t0 =3.0; if the target web hole is porous, then K t0 Consult the Stress Concentration Handbook for details.

6. The method for calculating local stress in the web opening of an aircraft structure based on a global finite element model according to claim 4, characterized in that, β w Calculate using the following formula: Where e is the distance from the web hole to the frame / beam edge strip in the direction of maximum principal stress, and d is the diameter of the web hole.

7. The method for calculating local stress in the web opening of an aircraft structure based on a global finite element model according to claim 4, characterized in that, β bi Calculate using the following formula: Where σ1 and σ2 are the maximum and minimum principal stresses in the plane of the corresponding web element in the overall finite element model, respectively.

8. The method for calculating local stress in the web opening of an aircraft structure based on a global finite element model according to claim 4, characterized in that, If it is a single-sided boss, β pad =1.1, if it is a double-sided boss, β pad Obtained by consulting the Stress Concentration Handbook.

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