Airplane stringer and skin circumferential connection detail fatigue rated value determination method

Abstract

The invention discloses an airplane stringer and skin circumferential connection detail fatigue rated value determination method. The method comprises the following steps: S1, establishing a to-be-calculated common frame stringer and skin circumferential connection component finite element model; s2, applying a unit load, and analyzing the relationship between the extrusion stress of each component at the fastener and the gross area stress at the fastener in the model through a finite element; calculating a fatigue rated value of each detail part of each component according to a detail fatigue strength calculation method, and determining the most dangerous part of the connecting assembly; and S3, uniformly converting the fatigue rated values corresponding to all the components to a reference surface, and obtaining the fatigue rated values of all details of the common frame stringer and skin circumferential connecting assembly. According to the method, the situation that dangerous parts are missed to be checked due to subtle differences between structures or uniqueness of the structures is avoided, and the calculation result is more accurate.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of aircraft structure fatigue strength calculation, and particularly relates to a method for determining fatigue rating of a circumferential connection detail of a long stringer and a skin of an aircraft. BACKGROUND

[0002] At present, when calculating the fatigue life of the circumferential connection of the ordinary frame long stringer and the skin of a transport aircraft fuselage, the DFR method is generally used for calculation. In general, the engineering method is used to calculate the fatigue rating of each component detail, without considering the influence of the row number and stiffness of the long stringer connecting piece and the long stringer connecting piece and the frame edge, strap plate, skin connecting fastener on the fatigue performance. It cannot be achieved to survey each detail part, and it is impossible to avoid the situation that the dangerous part is missed due to the slight difference between structures or the uniqueness of the structure, and the calculation result is not accurate. SUMMARY

[0003] The purpose of the application is to provide a method for determining the fatigue rating of the circumferential connection detail of the long stringer and the skin of an aircraft. The application avoids the situation that the dangerous part is missed due to the slight difference between structures or the uniqueness of the structure, and the calculation result is more accurate.

[0004] To achieve the above purpose, the application adopts the following technical scheme. A method for determining the fatigue rating of the circumferential connection detail of the long stringer and the skin of an aircraft, comprising: S1. Establishing a finite element model of the ordinary frame long stringer and the circumferential connection assembly to be calculated; S2. Applying unit load, and obtaining the relationship between the extrusion stress of each component at the fastener and the gross area stress at the fastener in the finite element analysis model; calculating the fatigue rating of each detail part of each component according to the detail fatigue strength calculation method, and determining the most dangerous part of the connection assembly; S3. Converting the corresponding fatigue rating of each component to a reference surface to obtain the fatigue rating of each detail of the ordinary frame long stringer and the circumferential connection assembly.

[0005] In the aforementioned method for determining the fatigue rating of the circumferential connection detail of the long stringer and the skin of an aircraft, in S1, when establishing the finite element model, the fastener flexibility is based on f The fastening degree of the fastener is represented as:

[0006] wherein, t 1, t 2 represent the thickness of the base body and the strap plate, E 1, E 2, E f represent the elastic modulus of the base body, the strap plate and the fastener material, d represents the diameter of the fastener.

[0007] In the method for determining the fatigue rating of the circumferential connection details of the aircraft longerons and skins, in S2, the relationship between the extrusion stress of each component at the fastener and the bare area stress at the fastener is analyzed as follows: the nail load transmission of each component is obtained through finite element calculation, the extrusion stress of each component at the fastener is obtained, and thus the relationship between the extrusion stress of each component at the fastener and the bare area stress at the fastener is obtained.

[0008] In the method for determining the fatigue rating of the circumferential connection details of the aircraft longerons and skins, in S2, the most dangerous position of the connection assembly is determined as follows: according to the detail fatigue strength calculation method, the fatigue rating of each detail position of each component is obtained, and the position with the smallest fatigue rating is the most dangerous position of the component.

[0009] In the method for determining the fatigue rating of the circumferential connection details of the aircraft longerons and skins, in S2, the fatigue rating of each detail position of each component DFR dd The calculation is as follows: , DFR base is the fatigue rating strength reference value of the detail position of the component, A is the hole filling coefficient, B is the alloy and surface treatment coefficient, C is the countersunk depth coefficient for various alloys, D is the material lamination coefficient, E is the bolt clamping coefficient of various alloys, U is the boss effective coefficient, R c is the component fatigue rating coefficient.

[0010] In the method for determining the fatigue rating of the circumferential connection details of the aircraft longerons and skins, DFR base The calculation is as follows: , Ψ is the load transmission coefficient.

[0011] In the method for determining the fatigue rating of the circumferential connection details of the aircraft longerons and skins, Ψ The calculation is as follows: , , f br is the extrusion stress of the component at the fastener hole, f tThe stress is the gross area stress at the fastener of the component. R The compressive force at the fastener holes on the component cross-section. t For the thickness of the component section, d For the diameter of the fastener, P The resultant force is the gross area of ​​the entire cross-section of the component perpendicular to the direction of force at the fastener. Aria This represents the gross area of ​​the component's cross-section.

[0012] In the aforementioned method for determining the fatigue rating of the circumferential connection details of aircraft stringers and skin, Ψ When the value is greater than 1, take the value 1.

[0013] In the aforementioned method for determining the fatigue rating of details in the circumferential connection of aircraft stringers and skin, in S3, the fatigue rating of each detail in the circumferential connection assembly of ordinary frame stringers and skin is... DFR The calculation is as follows: , , DFR dd These are the fatigue ratings for detailed parts of the component. ckxs This represents the reference coefficient used to convert local stress values ​​into reference surface stress values. σ This represents the assumed reference surface stress value. f t The stress is the gross area stress at the fastener of the component.

[0014] Beneficial effects: This invention systematically considers the load-bearing characteristics of the structure, and also considers the influence of the number of rows and stiffness of the stringers and the connecting fasteners between the stringers and the frame edge, strip plate, and skin on fatigue performance. It can conduct a comprehensive inspection of all detailed parts, avoiding the omission of dangerous parts due to subtle differences between structures or the uniqueness of the structure, and the calculation results are more accurate.

[0015] The method for determining the fatigue rating of the circumferential connection details of the ordinary frame stringer and skin of an aircraft proposed in this invention has a clear theoretical basis, simple steps, and is easy to automate calculations through computer programming. Attached Figure Description

[0016] Figure 1 A flowchart illustrating a method for determining fatigue ratings of circumferential connections between an aircraft stringer and skin, provided in an embodiment of the present invention. Figure 2 A schematic diagram of a common frame truss and skin circumferential connection structure provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of a finite element model of a common frame truss and skin circumferential connection structure provided in an embodiment of the present invention. Detailed Implementation

[0017] The features and illustrative embodiments of various aspects of the present invention will now be described in detail. Numerous specific design details are set forth in the following detailed description to provide a more complete understanding of the invention. However, it will be apparent to those skilled in the art that the invention can be practiced without some of these specific details. The following description of embodiments is merely intended to provide a better understanding of the invention by illustrating examples of the invention. The invention is by no means limited to any specific setup and method set forth below, but covers any improvements, substitutions, and modifications to the structures, methods, and devices without departing from the spirit of the invention. In the drawings and the following description, any parts not exhaustively described are considered to be common knowledge or conventional practices in the art.

[0018] It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other, and the various embodiments can be referenced and cited in each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0019] Example 1. This invention provides a method for determining the fatigue rating of the connection details between an aircraft stringer and skin. The main steps are as follows: Figures 1-3 As shown: Step 1: Determine the circumferential connection parts of the ordinary frame girder and skin to be calculated, establish a finite model of the circumferential connection components of the ordinary frame girder and skin, and simulate the fasteners connecting the components (including skin, girder joints, girder, frame edge, pad, girder corner piece). Step 2: Apply a unit load and obtain the load transmitted by the fasteners of each component through finite element analysis. This yields the magnitude of the compressive stress on each component at the fastener, allowing for the determination of the relationship between the compressive stress and the gross area stress at the fastener. Based on the detailed fatigue strength calculation method, determine the fatigue rating of each component at each detailed location. The location with the lowest fatigue rating is the most critical location for that component. Step 3: Convert the fatigue rating values ​​of each component to the reference plane to obtain the fatigue rating values ​​of each component (relative to the reference plane) of the ordinary frame girder and skin circumferential connection components.

[0020] In step 1, when establishing the finite element model, based on the fastener compliance... f Characterizing the tightness of fasteners:

[0021] in, t 1. t 2 represents the thickness of the matrix and the strip, respectively. E 1. E 2. E fThese represent the elastic moduli of the matrix, strip, and fastener materials, respectively. d This indicates the diameter of the fastener.

[0022] Step 2, the method for calculating the fatigue strength of each component and its detailed parts:

[0023]

[0024]

[0025]

[0026] in, DFR base This is the benchmark value for the fatigue rated strength of the detailed parts of the component. A The pore filling coefficient is... B For alloy and surface treatment coefficients, C This is the countersinking depth coefficient used for various alloys. D The material stacking factor, E For various alloys, the bolt clamping factor is... U This is the effective coefficient of the boss. R c The component fatigue rating factor (depending on the number of similar critical details in the structure). Ψ is the load transfer factor. f br This refers to the compressive stress at the fastener holes of the component. f t The stress is the gross area stress at the fastener of the component. R The compressive force at the fastener holes on the component cross-section. t For the thickness of the component section, d For the diameter of the fastener, P The resultant force is the gross area of ​​the entire cross-section of the component perpendicular to the direction of force at the fastener. Aria This represents the gross area of ​​the component's cross-section.

[0027] In step 3, the fatigue rated strength of the component details (relative to the reference surface):

[0028] in, ckxs This represents the reference coefficient used to convert local stress values ​​into reference surface stress values. DFR Indicates the fatigue rated strength of a detailed part of the component (relative to the reference surface). σ This represents the assumed reference surface stress value.

[0029] This invention proposes a method for determining the fatigue rating of details in the circumferential connection of aircraft stringers and skin, which systematically considers the load-transfer characteristics of the structure. Current engineering methods for determining fatigue ratings of details are too simplistic, failing to consider the circumferential connection characteristics of the fuselage, resulting in insufficient calculation accuracy. This invention considers the influence of the number of rows and stiffness of stringer-to-stringer connectors, stringer connectors and frame edges, strips, and skin fasteners under tension on fatigue performance. It truly achieves a comprehensive survey of all detailed parts, accurately calculating the fatigue ratings of details in the stringer, stringer joints, frame edges, mating strips, and each fastening hole of the mating skin based on the same reference stress. This avoids overlooking dangerous areas due to subtle differences or unique structural features, resulting in more accurate calculations. The method for determining the fatigue rating of details in the circumferential connection of aircraft stringers and skin proposed in this invention has a clear theoretical basis, simple steps, and is easy to automate using computer programming.

[0030] The above description is merely a specific embodiment of the present invention, but 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 technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for determining the fatigue rating of details in the circumferential connection of an aircraft stringer and skin, characterized in that, Comprise: S1. Establish the finite element model of the common frame stringer, skin circumferential connection assembly to be calculated; S2. Apply unit load, through the relationship between the extrusion stress of each component at the fastener and the bare area stress at the fastener in the finite element analysis model; according to the detail fatigue strength calculation method, calculate the fatigue rating of each detail part of each component, and determine the most dangerous part of the connection assembly; S3. The corresponding fatigue rating of each component is uniformly converted to the reference surface to obtain the detail fatigue rating of the common frame stringer, skin circumferential connection assembly.

2. The method of determining a fatigue rating for a stringer-to-skin circumferential joint detail of an aircraft as defined in claim 1, wherein, In S1, when establishing the finite element model, based on the flexibility of the fastener f Characterize the fastening degree of the fastener: wherein, t 1, t 2denote the substrate, the strap thickness, E 1, E 2, E f denote the substrate, the strap, the fastener material modulus of elasticity, d denotes the fastener diameter.

3. The method of determining a fatigue rating for a stringer-to-skin circumferential joint detail of an aircraft as defined in claim 1, wherein, In S2, the relationship between the extrusion stress of each component at the fastener and the bare area stress at the fastener is analyzed as follows: the fastener nail load of each component is obtained by finite element calculation, the extrusion force of each component at the fastener is obtained, and the relationship between the extrusion stress of each component at the fastener and the bare area stress at the fastener is obtained.

4. The method of determining a fatigue rating for a stringer-to-skin circumferential joint detail of an aircraft according to claim 1, wherein, In S2, the determination of the most dangerous part of the connection assembly is as follows: according to the detail fatigue strength calculation method, the fatigue rating of each detail part of each component is calculated, and the part with the smallest fatigue rating is the most dangerous part of the component.

5. The method of determining a fatigue rating for a stringer-to-skin circumferential joint detail of an aircraft as defined in claim 1, wherein, In S2, the fatigue rating of each component and each detail DFR dd The calculation is as follows: ， DFR base Fatigue rating reference value for member detail, A Bore fill factor, B Alloy and surface treatment factor, C Countersunk depth factor for various alloys, D Material stackup factor, E Bolt clamping factor for various alloys, U Boss effective factor, R c Part fatigue rating factor.

6. The method of determining a fatigue rating for a stringer-to-skin circumferential joint detail of an aircraft as defined in claim 5, wherein, DFR base The calculation is as follows: ， Ψ is the load transmission coefficient.

7. The method of determining a fatigue rating for a stringer-to-skin circumferential joint detail of an aircraft as defined in claim 6, wherein, Ψ The calculation is as follows: ， ， f br Extrusion stress at the fastener hole of the component, f t Matted area stress at the fastener of the component, R Extrusion force at the fastener hole of the component cross section, t Component cross section thickness, d Fastener diameter, P Matted area resultant force at the fastener of the component cross section perpendicular to the force direction, Aria Matted area of the component cross section.

8. The method of determining a fatigue rating for a stringer-to-skin circumferential joint detail of an aircraft as defined in claim 7, wherein, Ψ >1, take 1.

9. The method of determining a fatigue rating for a stringer-to-skin circumferential joint detail of an aircraft according to claim 1, wherein, In S3, the fatigue rating of each detail of the common frame longerons, skin circumferential joint assemblies DFR The calculation is as follows: ， ， DFR dd Fatigue rating for detail of member, ckxs represents a reference coefficient to convert a local stress value into a reference surface stress value, σ represents a hypothetical reference surface stress value, f t Area stress at fastener of member.

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