Overall finite element model-based aircraft structure web tapping local stress calculation method

Abstract

The invention discloses an aircraft structure web tapping local stress calculation method based on an overall finite element model. The method comprises the following steps: extracting gross section reference stress based on a stress analysis result of the overall finite element model; determining a stress concentration coefficient according to the geometric dimension of the opening and the stress state of the web unit; and based on section rigidity loss caused by trepanning and compensation of the boss on the section rigidity, a trepanning load reduction coefficient is introduced, and finally the local stress of the web hole edge is determined. According to the method, the local detail stress of various web openings of the aircraft structure can be quickly determined, so that structural strength design is facilitated.

Description

Technical Field

[0001] The invention belongs to the field of aircraft structure strength, and in particular relates to a method for calculating local stress of an opening in a web of an aircraft structure based on an overall finite element model. Background Art

[0002] Web holes are one of the most common, important and typical structural details in aircraft structures. In the process of aircraft design and development, detailed stress analysis is usually used to obtain the local stress around the web holes. However, this method has a complex calculation process and requires high computing and human resources, which restricts the rapid iteration of aircraft structural design. Summary of the invention

[0003] The purpose of the present invention is to provide a method for calculating the local stress of the web opening of an aircraft structure based on an overall finite element model. The present invention can quickly determine the local detail stress of various web openings of the aircraft structure so as to perform structural strength design.

[0004] The technical solution is as follows: a method for calculating the local stress of the web opening of an aircraft structure based on the overall finite element model, extracting the gross section reference stress based on the stress analysis results of the overall finite element model; determining the stress concentration factor according to the geometric dimensions of the opening and the stress state of the web unit; introducing the opening load reduction factor based on the section stiffness loss caused by the opening and the compensation of the section stiffness by the boss, and finally determining the local stress at the edge of the web hole.

[0005] In the above-mentioned calculation method of local stress of the web opening of aircraft structure based on the overall finite element model, the local stress of the web hole edge is calculated as follows:

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

[0007] Among them, σ max is the local stress at the hole edge, σ ref represents the gross cross-section reference stress, K t is the stress concentration factor, β loss is the opening load reduction factor.

[0008] The aforementioned method for calculating the local stress of the opening in the web of an aircraft structure based on the overall finite element model comprises the following steps:

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

[0010] S2. For the web hole described in step S1, according to the geometric dimensions of the opening and the stress state of the web unit, the stress concentration factor K is calculated based on the stress concentration factor of the uniaxial infinite width plate hole, taking into account the finite width correction, hole shape correction, biaxial stress correction and boss correction. t ;

[0011] S3. For the web hole described 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 the local stress of the web opening of an aircraft structure based on the overall finite element model, in step S1, if the opening is located in the middle area of ​​the web, the principal stress of the web unit is used as the reference stress of the gross section of the web hole.

[0014] In the aforementioned method for calculating local stress of a web opening of an aircraft structure based on an overall finite element model, in step S1, if the opening is located in the edge area of ​​the web, the principal stress of the nearest node is used as the gross cross-section reference stress of the web hole.

[0015] In the above-mentioned method for calculating the local stress of the opening in the web of an aircraft structure based on the overall finite element model, in step S2, the stress concentration factor K t The calculation method is:

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

[0017] In the formula, K t0 is the reference stress concentration factor of the uniaxial infinite width plate hole; β w is the finite width correction factor; β elip is the hole shape correction factor; β bi is the biaxial stress correction factor; β pad is the boss correction factor.

[0018] In the above-mentioned calculation method of local stress of aircraft structure web opening based on the overall finite element model, if the target web hole is a single hole, then K t0 =3.0; if the target web hole is multi-hole, then K t0 Consult the Stress Concentration Handbook to obtain it.

[0019] In the above-mentioned calculation method of local stress of opening in aircraft structure web based on overall finite element model, β w Calculate as follows:

[0020] β w =1.0(e / d>2)

[0021] β w =1.1(e / d≤2)

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

[0023] In the above-mentioned calculation method of local stress of opening in aircraft structure web based on overall finite element model, β bi Calculate as follows:

[0024] β bi =1-σ2 / σ1 / 3

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

[0026] In the above-mentioned calculation method of local stress of opening in aircraft structure web based on overall 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 above-mentioned calculation method of local stress of opening in aircraft structure web based on overall finite element model, β loss Calculate as follows:

[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 hole diameter of the web, W is the target web panel width perpendicular to the direction of maximum principal stress, β pad is the boss correction factor.

[0031] Beneficial effects: The web opening is one of the most extensive, important and typical structural details in aircraft structures, and fatigue cracks often occur due to stress concentration. The present invention is based on the analysis results of the overall finite element model of the aircraft structure, and can quickly calculate the local stress at the edge of the web hole, and comprehensively considers the influence of factors such as the geometric size of the web hole, the plane stress state, and the reduction of the opening load, thereby ensuring the accuracy of the calculation results, avoiding the complex detailed stress analysis of the calculation process, and greatly improving the fatigue strength analysis efficiency of the web holes of the aircraft structure, thereby realizing the rapid iterative optimization design of the aircraft structure details in engineering and the durability analysis covering the entire aircraft load-bearing structure. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0034] Figure 3 It is the principal stress cloud diagram of the overall finite element model corresponding to the target web hole in the example; (a) is the maximum principal stress cloud diagram of the plate unit, and (b) is the minimum principal stress cloud diagram of the plate unit. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not 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.

[0036] Example 1. A method for calculating local stress of openings in the web of an aircraft structure based on an overall finite element model, see Figure 1-Figure 3 , taking a web hole near a fuselage frame edge strip of a certain type of aircraft as an example (see Figure 2 ), a method for calculating the local stress of the opening in the web of an aircraft structure is described; the steps are as follows:

[0037] 1) For the web hole, determine the gross section reference stress σ according to the stress state of the corresponding web unit in the overall finite element model: ref ;

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

[0039] 2) According to 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 t0 =3.0;

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

[0042] The web hole is an oblong elliptical hole. According to the actual structural size, the hole shape correction factor β is calculated by consulting the stress concentration factor manual. elip =0.84;

[0043] The maximum principal stress of the web hole is σ1 = 232MPa, the minimum principal stress is σ2 = -125MPa, 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. According to the actual structural size, the boss correction factor β is calculated by referring to the stress concentration factor manual. 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 web hole diameter d = 43mm, the web grid width W = 140mm, and the opening load reduction factor 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 web hole;

[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 of openings in the web of an aircraft structure based on an overall finite element model, see Figure 1 The idea of ​​the present invention is to first extract the gross section reference stress based on the stress analysis results of the overall finite element model; and determine the stress concentration factor according to the opening geometry and the stress state of the web unit; at the same time, considering the actual section stiffness loss caused by the opening and the compensation of the section stiffness by the boss, the opening load reduction factor is introduced to quickly determine the local stress at the web hole edge. The calculation formula for the local stress at the web hole edge is as follows:

[0051] σ max =σ ref *K t *(1-β loss )

[0052] Among them, σmax is the local stress at the hole edge, σ ref represents the gross cross-section reference stress, K t is the stress concentration factor, β loss is the opening load reduction factor, and the local stress mentioned in the present invention refers to the local linear elastic stress.

[0053] The calculation steps are as follows:

[0054] S1: For the target web hole to be analyzed, determine the gross section reference stress σ according to 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 planar maximum principal stress σ1 and the planar 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 area of ​​the web, the web unit principal stress is used as the gross cross-section reference stress of the web hole.

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

[0058] S2: For the web hole described in S1, according to the geometric size of the opening and the stress state of the web unit, the stress concentration factor K is calculated based on the stress concentration factor of the uniaxial infinite width plate hole, taking into account the finite width correction, hole shape correction, biaxial stress correction and boss correction. t ;

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

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

[0061] K t0 is the reference stress concentration factor of the uniaxial infinite width plate hole. If the target web hole is a single hole, then K t0 is 3.0; if the target web hole is porous, then K t0 It is related to factors such as the number of holes, hole size, relative position, etc., and can be obtained by referring to the relevant stress concentration manual.

[0062] β w is the finite width correction factor, which indicates the influence of the finite width plate on the local stress and 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 edge distance from the web hole to the frame / beam flange in the direction perpendicular to the maximum principal stress, and d is the hole diameter of the web hole.

[0066] β elip It is the hole shape correction factor, which indicates the influence of the hole shape (which can be divided into round hole, elliptical hole, oblong hole and square hole) on the local stress. It can be obtained by referring to the relevant stress concentration manual.

[0067] β bi is the biaxial stress correction factor, which represents the influence of the stress state of the web element on the local stress. The calculation method is:

[0068] β bi =1-σ2 / σ1 / 3

[0069] Among them, σ1 and σ2 are the maximum principal stress and the minimum principal stress of the plane described in S1, respectively.

[0070] β pad is the boss correction coefficient, which indicates the influence of the reinforced boss of the web hole on the local stress. It is related to the size of the boss and the system hole. 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 of can be obtained by referring to the relevant stress concentration manual.

[0071] S3: For the web hole described in S1, calculate the opening load reduction factor according to the actual web hole structure size;

[0072] In step S3, since the web element of the overall finite element model usually does not reflect the opening, the opening load reduction factor β is used. loss To characterize the loss of section stiffness caused by the opening and the compensation of the section stiffness by the boss, the calculation method is:

[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 hole diameter of the web, W is the target web panel width perpendicular to the direction of maximum principal stress, β pad is the boss correction factor 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 hole edge of the target web;

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

[0078] The above is only a specific embodiment of the present invention, and the present invention is described in detail. The unexplained part is a conventional technology. However, the protection scope of the present invention is not limited to this. Any changes or substitutions that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. The protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A method for calculating local stress of openings in webs of aircraft structures based on an overall finite element model, characterized in that: Extract gross cross-section reference stress based on stress analysis results of the overall finite element model; Determine the stress concentration factor based on the opening geometry and the web element stress state; Based on the section stiffness loss caused by the opening and the compensation of the section stiffness by the boss, the opening load reduction factor is introduced to finally determine the local stress at the hole edge of the web.

2. The method for calculating local stress of openings in the web of an aircraft structure based on an overall finite element model according to claim 1, characterized in that: The local stress at the hole edge of the web is calculated as follows: s max =s ref *K t *(1-b loss ) (1) Among them, σ max is the local stress at the hole edge, σ ref represents the gross cross-section reference stress, K t is the stress concentration factor, β loss is the opening load reduction factor.

3. The method for calculating local stress of openings in the web of an aircraft structure based on an overall finite element model according to claim 2, characterized in that: The following steps are involved: S1. For the web hole being analyzed, determine the gross section reference stress σ according to the stress state of the corresponding web element in the overall finite element model ref ;; S2. For the web hole described in step S1, according to the geometric dimensions of the opening and the stress state of the web unit, the stress concentration factor K is calculated based on the stress concentration factor of the uniaxial infinite width plate hole, taking into account the finite width correction, hole shape correction, biaxial stress correction and boss correction. t ; S3. For the web hole described 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.

4. The method for calculating local stress of openings in the web of an aircraft structure based on an overall finite element model according to claim 3, characterized in that: In step S1, if the opening is located in the middle area of ​​the web, the web element principal stress is used as the gross cross-section reference stress of the web hole.

5. The method for calculating local stress of openings in the web of an aircraft structure based on an overall finite element model according to claim 3, characterized in that: In step S1, if the opening is located in the edge area of ​​the web, the principal stress of the nearest node is used as the reference stress of the gross section of the web hole.

6. The method for calculating local stress of openings in the web of an aircraft structure based on an overall finite element model according to claim 3, characterized in that: In step S2, the stress concentration factor K t The calculation method is: K t =b pad *(K t0 *b w *b elip *b bi -1)+1 In the formula, K t0 is the reference stress concentration factor of the uniaxial infinite width plate hole; β w is the finite width correction factor; β elip is the hole shape correction factor; β bi is the biaxial stress correction factor; β pad is the boss correction factor.

7. The method for calculating local stress of openings in the web of an aircraft structure based on an overall finite element model according to claim 6, characterized in that: If the target web hole is a single hole, then K t0 =3.0; if the target web hole is multi-hole, then K t0 Consult the Stress Concentration Handbook to obtain it.

8. The method for calculating local stress of openings in webs of aircraft structures based on an overall finite element model according to claim 6, characterized in that: β w Calculate as follows: b w =1.0(e / d>2) b w =1.1(e / d≤2) Where, e is the edge distance from the web hole to the frame / beam flange in the direction perpendicular to the maximum principal stress, and d is the hole diameter of the web hole.

9. The method for calculating local stress of openings in webs of aircraft structures based on an overall finite element model according to claim 6, characterized in that: β bi Calculate as follows: b bi =1-σ2 / σ1 / 3 Among them, σ1 and σ2 are the plane maximum principal stress and plane minimum principal stress of the corresponding web element in the overall finite element model, respectively.

10. The method for calculating local stress of openings in webs of aircraft structures based on an overall finite element model according to claim 6, 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.

Images