Aircraft fastener load calculation method

Abstract

The invention provides a method for calculating the load of an aircraft fastener, which comprises the following steps of: calculating the axial rigidity, the shearing rigidity, the torsional rigidity and the bending rigidity of the fastener according to the effective length, the diameter and the material of the fastener; according to the coordinate value of the fastener and the coordinate value of the load action point, a fastener partial load finite element model is established by adopting finite element software, and the fastener partial load finite element model is endowed with fastener attributes; according to the boundary condition and the load working condition, calculating and extracting a fastener load; pulling force or pressure and shearing force borne by all the fasteners are settled, and the pulling force or pressure and shearing force borne by the fasteners are integrated, namely the load borne by the fasteners after load division. The problems that an existing load calculation mode for the fastener is complex in calculation step and large in calculation amount are solved.

Description

Technical Field

[0001] This invention belongs to the field of aircraft structural strength design, and in particular relates to a method for calculating the load on aircraft fasteners. Background Technology

[0002] Fasteners are fundamental components of aircraft structures, widely used in various structural connections, equipment, and piping installations, and found throughout every part of the aircraft. An aircraft may contain hundreds of thousands, or even millions, of fasteners. During their service life, aircraft structural fasteners are subjected not only to static loads but also to alternating loads generated by factors such as takeoff and landing, engine vibrations, high-speed rotation of rotating parts, maneuvering, and gusts. Fasteners have a significant impact on the strength and lifespan of the aircraft structure, playing a crucial role in the aircraft's weight, reliability, and maintainability. Accurately calculating the loads on fasteners is essential for strength design.

[0003] Currently, analytical methods are commonly used to calculate the loads on aircraft structural fasteners. The traditional method involves establishing a three-dimensional Cartesian coordinate system, determining the centroid of the fastener group using analytical or graphical methods based on the fastener diameter and coordinate values, and then translating the load to this centroid. The shear force of the fasteners at different locations is then calculated based on their characteristics; the tensile or compressive forces are also calculated based on these characteristics. The shear, tensile, or compressive forces acting on the fasteners at different locations are then aggregated, and the combined shear, tensile, or compressive forces represent the load on the fasteners after load distribution, thus completing the fastener load allocation. This traditional method of fastener load calculation is complex and computationally intensive. Summary of the Invention

[0004] The purpose of this invention is to provide a method for calculating the load on aircraft fasteners, thereby solving the problems of complex calculation steps and large computational load in existing methods for calculating the load on fasteners.

[0005] The technical solution of this invention is as follows: This invention provides a method for calculating the load on aircraft fasteners, comprising the following steps: Step 1: Calculate the fastener stiffness based on the effective length, diameter, and material of the fastener. Fastener stiffness includes: axial stiffness, shear stiffness, torsional stiffness, and bending stiffness. Step 2: Based on the coordinate values ​​of the fastener and the coordinate values ​​of the load application point, establish a finite element model of the fastener under load using finite element software, and assign fastener properties to the finite element model of the fastener under load. Step 3: Calculate and extract the fastener load based on the boundary conditions and load conditions; Step 4: Compile all the tensile, compressive, and shear forces on the fasteners. The total tensile, compressive, and shear forces on the fasteners are the loads on the fasteners after load distribution.

[0006] Optionally, in the method for calculating aircraft fastener load as described above, step 1 includes: The axial stiffness of the fastener is calculated based on its effective length, diameter, and material parameters. shear stiffness and Torsional stiffness Bending stiffness and They are respectively: ; ; ; ; ; ; In the formula, The elastic modulus of the fastener material. Let this be the cross-sectional area of ​​the fastener. The effective length of the fastener. For the polar moment of inertia of the fastener, Let the moment of inertia of the fastener section be , This represents the equivalent area of ​​the fastener. Let be a constant, take , This is the shear modulus of the fastener material.

[0007] Optionally, in the aircraft fastener load calculation method described above, step 2 involves using finite element software to establish a finite element model of the fastener load distribution, including: Based on the coordinate values ​​of the fastener and the coordinate values ​​of the load application point, fastener nodes and load application nodes are established respectively. Heavy nodes are established at the positions of each fastener node. Fastener nodes and heavy nodes with the same position are connected to establish spring element CELAS2. Based on the fact that the fastener has 6 stiffnesses, each heavy node has 6 spring elements CELAS2. With the load application node (1001) as the master node and the fastener node as the slave node, rigid body element RBE2 is established.

[0008] Optionally, in the aircraft fastener load calculation method described above, step 2, assigning fastener properties to the fastener load-sharing finite element model, includes: In the finite element software, assign axial stiffness, shear stiffness, torsional stiffness, and bending stiffness properties to the spring element CELAS2.

[0009] Optionally, in the aircraft fastener load calculation method described above, step 3 includes: Based on the boundary conditions of the actual structure, constrain the corresponding degrees of freedom of the fastener heavy nodes in the spring element CELAS2, apply loads to the main nodes of the RBE2 element according to the actual load conditions, and calculate and extract the fastener loads.

[0010] Optionally, in the aircraft fastener load calculation method described above, the aircraft structure is a fuselage pylon front joint, and the fasteners used on the fuselage pylon front joint are bolts; the fuselage pylon front joint material is 7050 aluminum alloy, the fastener material is 30CrMnSiA, and the elastic modulus of the fastener material is... shear modulus ; Step 2, which involves establishing the finite element model of the fastener, includes: Step 21: Obtain the fastener coordinate values ​​based on the fastener digital model, establish fastener nodes in the finite element software based on each coordinate value, and obtain the coordinate values ​​of the fastener load application point, and establish load application nodes in the finite element software. Step 22: Establish heavy nodes at each fastener node position, connect fastener nodes and heavy nodes with the same position to establish spring element CELAS2. Based on the fact that the fastener has 6 stiffnesses, each heavy node has 6 spring elements CELAS2; with the load-acting node (1001) as the master node and the fastener node as the slave node, establish rigid body element RBE2.

[0011] Optionally, in the aircraft fastener load calculation method described above, step 2, assigning fastener properties to the fastener load-sharing finite element model, includes: Based on the fastener direction in the actual structure, the spring element CELAS2 is given axial stiffness, shear stiffness, torsional stiffness and bending stiffness to ensure that the six spring elements CELAS2 at the heavy nodes can realistically simulate the fastener stiffness.

[0012] Optionally, in the aircraft fastener load calculation method described above, step 4 includes: By summing the tensile, compressive, and shear forces acting on the spring element CELAS2 at the same node position, the total tensile, compressive, and shear forces acting on the spring element CELAS2 are obtained as the load on each fastener after load distribution.

[0013] The beneficial effects of this invention are as follows: This invention provides a method for calculating the load on aircraft fasteners. First, the fastener stiffness is calculated based on the effective length, diameter, and material parameters of the fastener. Second, a finite element model of the fastener under load is established based on the fastener coordinates and the coordinates of the load application point, and fastener properties are assigned to the finite element model. Third, the fastener load is calculated and extracted based on boundary conditions and load conditions. Finally, the tensile or compressive and shear forces acting on all fasteners are collected, and the combined tensile or compressive and shear forces acting on the fasteners are the load on the fasteners after load distribution. The method for calculating the load on aircraft fasteners provided by this invention solves the shortcomings of traditional methods, such as complex calculation steps and large computational load. Specifically, it has the following beneficial effects: 1) The method provided by this invention can accurately and quickly calculate the fastener load; 2) Compared with traditional methods, the method provided by this invention solves the shortcomings of complex calculation steps and large amount of calculation, and meets the requirements of rapid iteration of structural schemes; 3) The method provided by this invention is simple to operate, realizes the standardization of fastener load calculation method, and provides aircraft designers with a method for calculating aircraft fastener load. Attached Figure Description

[0014] The accompanying drawings are provided to further understand the technical solutions of the present invention and constitute a part of the specification. They are used together with the embodiments of this application to explain the technical solutions of the present invention and do not constitute a limitation on the technical solutions of the present invention.

[0015] Figure 1 Schematic diagram of the front connector of the fuselage mounting bracket; Figure 2 A schematic diagram of a finite element model of a fastener under load. Figure 3 A schematic diagram showing the numbering of nodes in the finite element model of the fastener under load. Figure 4 This is a diagram showing the numbering of fasteners.

[0016] Explanation of reference numerals in the attached figures: 1-Front connector of fuselage bracket, 2-Fixed finite element model of fasteners, 3-Fastener number. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

[0018] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0019] As explained in the background section, fasteners are widely used in aircraft structures for various structural connections, equipment, and piping installations, and are found throughout various parts of the aircraft. Accurately calculating the load on fasteners is crucial for strength design. However, existing methods for calculating the load on fasteners suffer from complex calculation steps and a large computational load.

[0020] For fastener strength design, the ability to conveniently, accurately, and quickly calculate fastener loads is crucial to aircraft flight safety, economy, and maintainability. Therefore, it is necessary to establish a method for calculating aircraft fastener loads to facilitate convenient, accurate, and rapid fastener strength design.

[0021] Based on the above requirements, the present invention provides a method for calculating the load of aircraft fasteners, which is based on the finite element method, with the aim of conveniently, accurately and quickly calculating the load of aircraft fasteners.

[0022] The present invention provides the following specific embodiments, which can be combined with each other. For the same or similar concepts or processes, they may not be described again in some embodiments.

[0023] This invention provides a method for calculating the load on aircraft fasteners. This method is based on static strength calculation using finite element analysis. First, the fastener stiffness is calculated according to the effective length, diameter, and material parameters of the fastener. Second, a finite element model of the fastener under load is established based on the coordinates of the fastener and the load application point, and fastener properties are assigned to this model. Third, the fastener load is calculated and extracted based on boundary conditions and load conditions. Finally, all tensile or compressive and shear forces acting on the fasteners are collected, and the combined tensile or compressive and shear forces are the load on the fasteners after load distribution. Using the calculation method provided by this invention, the load on aircraft fasteners can be calculated quickly, conveniently, and accurately.

[0024] The method for calculating aircraft fastener loads provided by this invention mainly includes the following steps: S1. The axial stiffness of the fastener is calculated using the following formula based on the effective length, diameter, and material parameters of the fastener. shear stiffness and Torsional stiffness Bending stiffness and ; ; ; ; ; ; ; In the formula, The elastic modulus of the fastener material. Let this be the cross-sectional area of ​​the fastener. The effective length of the fastener. For the polar moment of inertia of the fastener, Let the moment of inertia of the fastener section be , This represents the equivalent area of ​​the fastener. It is a constant, generally taken as , This is the shear modulus of the fastener material.

[0025] Axial stiffness refers to the ability to resist tensile or compressive deformation along the axis of the fastener; shear stiffness refers to the ability to resist shear deformation perpendicular to the axis of the fastener. Torsional stiffness refers to the ability to resist torsional deformation about the axis of a fastener. Bending stiffness refers to the ability to resist rotation about an axis perpendicular to the axis of the fastener. For general problems, reference values ​​can be used for torsional stiffness and bending stiffness. Torsional stiffness... Take 100, bending stiffness and Take 100000000 S2. Based on the coordinate values ​​of the fastener and the coordinate values ​​of the load application point, a finite element model of the fastener under load is established using finite element software, and fastener properties are assigned to the finite element model of the fastener under load. In this step, a finite element model of the fastener under load is established using finite element software, including: Based on the coordinate values ​​of the fastener and the load application point, fastener nodes and load application nodes are established respectively. Heavy nodes are established at the positions of each fastener node. Fastener nodes and heavy nodes with the same position are connected to establish spring elements CELAS2. Since the fastener has 6 stiffnesses, each heavy node has 6 spring elements CELAS2. With load application node 1001 as the master node and fastener nodes as slave nodes, rigid body element RBE2 is established.

[0026] In this step, fastener properties are assigned to the fastener load finite element model, including: In the finite element software, assign axial stiffness, shear stiffness, torsional stiffness, and bending stiffness properties to the spring element CELAS2.

[0027] S3. Calculate and extract the fastener load based on the boundary conditions and load conditions; The implementation method of this step is as follows: constrain the corresponding degrees of freedom of the fastener heavy nodes in the spring element CELAS2 according to the boundary conditions of the actual structure, apply the load to the main node of the RBE2 element according to the actual load conditions, and calculate and extract the fastener load.

[0028] S4. Compile all the tensile, compressive, and shear forces on the fasteners. The sum of the tensile, compressive, and shear forces on the fasteners is the load on the fasteners after load distribution.

[0029] This invention provides a method for calculating the load on aircraft fasteners. First, the fastener stiffness is calculated based on its effective length, diameter, and material parameters. Second, a finite element model of the fastener under load is established based on the fastener's coordinates and the coordinates of the load application point, and fastener properties are assigned to this model. Third, the fastener load is calculated and extracted based on boundary conditions and load conditions. Finally, all tensile or compressive and shear forces acting on the fasteners are collected, and the combined tensile or compressive and shear forces are the load on the fasteners after load distribution. This method for calculating the load on aircraft fasteners overcomes the drawbacks of traditional methods, such as complex calculation steps and high computational load. Specifically, it has the following beneficial effects: 1) The method provided by this invention can accurately and quickly calculate the fastener load; 2) Compared with traditional methods, the method provided by this invention solves the shortcomings of complex calculation steps and large amount of calculation, and meets the requirements of rapid iteration of structural schemes; 3) The method provided by this invention is simple to operate, realizes the standardization of fastener load calculation method, and provides aircraft designers with a method for calculating aircraft fastener load.

[0030] The following examples illustrate the implementation of the aircraft fastener load calculation method provided in this invention.

[0031] Implementation Example 1 like Figures 1 to 4 As shown, taking the front connector of the aircraft fuselage pylon as an example, the material of the front connector of the fuselage pylon is 7050 aluminum alloy, the fastener material is 30CrMnSiA, the diameter is 5mm, the effective length is 7mm, and the elastic modulus of 30CrMnSiA material is... shear modulus The method for calculating the load on the fasteners of the front joint of the aircraft fuselage pylon includes the following steps: S1. Based on the digital model of the front connector of the aircraft fuselage pylon, the effective length of the fastener can be determined. ,diameter The fastener material is 30CrMnSiA. Referring to the "Practical Handbook of Engineering Materials," the elastic modulus of 30CrMnSiA is... shear modulus ; S2. Based on the formulas for calculating the axial stiffness, shear stiffness, torsional stiffness, and bending stiffness of fasteners, the axial stiffness of the fastener is obtained as follows: The shear stiffnesses are respectively and Torsional stiffness is The bending stiffnesses are respectively and ; S3. Obtain the fastener coordinate values ​​based on the fastener's digital model, which are (3062.767, -384.3, -47.0), (3088.767, -384.3, -47.0), (3062.767, -409.3, -47.0), (3088.767, -409.3, -47.0), (3062.767, -384.3, 47.0), (3088.767, -384.3, - ... 7, -384.3, 47.0), (3062.767, -409.3, 47.0) and (3088.767, -409.3, 47.0) were created sequentially in the finite element software, with node numbers ranging from 2001 to 2008. The load application point coordinates were (3076.767, -441.0, 0.0), and a load application node was created in the finite element software, with node number 1001. S4. Create duplicate nodes at positions 2001 to 2008, with node numbers sequentially from 3001 to 3008. Figure 3As shown, connecting two nodes at the same position establishes a spring element CELAS2. Each node has 6 spring elements CELAS2. The spring element CELAS2 numbers for nodes 2001 and 3001 are 2101, 2201, 2301, 2401, 2501, and 2601, respectively; the spring element CELAS2 numbers for nodes 2002 and 3002 are 2102, 2202, 2302, 2402, 2502, and 2602, respectively; the spring element CELAS2 numbers for nodes 2003 and 3003 are 2103, 2203, 2303, 2403, 2503, and 2603, respectively; and the spring element CELAS2 numbers for nodes 2004 and 3004 are 2104, 2201, 2301, 2401, 2501, and 2601, respectively. The spring element CELAS2 numbers for nodes 204, 2303, 2404, 2504, and 2604 with nodes 2005 and 3005 are 2105, 2205, 2305, 2405, 2505, and 2605, respectively. The spring element CELAS2 numbers for nodes 2006 and 3006 are 2106, 2206, 2306, 2406, 2506, and 2606, respectively. The spring element CELAS2 numbers for nodes 2007 and 3007 are 2107, 2207, 2307, 2407, 2507, and 2607, respectively. The spring element CELAS2 numbers for nodes 2008 and 3008 are 2108, 2208, 2308, 2408, 2508, and 2608, respectively. With load application node 1001 as the master node and fastener nodes 2001 to 2008 as slave nodes, a rigid body element RBE2 is established, with element number 3001. S5. Assign shear stiffness to spring elements 2101-2108. The attribute assigns shear stiffness 2201 to 2208 to the spring element. The attribute assigns axial stiffness to spring elements 2301 to 2308. The attribute assigns bending stiffness 2401 to 2408 to the spring element. The property assigns a bending stiffness of 2501 to 2508 to the spring element. The attribute assigns to spring elements 2601-2608 torsional stiffness. property; S6. Constraining spring elements 2101~2108, 2201~2208, 2301~2308, 2401~2408, 2501~2508, 2601~2608, nodes 3001~3008, translational degrees of freedom T1, T2, and T3. A vertical downward load of 1000N is applied to the master node 1001 of rigid body element RBE2. Based on the above-mentioned boundary conditions and applied load conditions, the element force of each spring element is calculated and extracted based on the fastener load-sharing finite element model with assigned properties. This is the fastener load, as shown in Table 1, where the load unit is N.

[0032] Table 1

[0033] S7. Record the tensile, compressive, and shear forces acting on all fasteners, and number the fasteners as follows: Figure 4 As shown in Table 2, the combined tensile or compressive force and shear force on the fastener constitute the load on the fastener after load distribution, where the unit of load is N.

[0034] Table 2

[0035] While the embodiments disclosed in this invention are as described above, they are merely illustrative of the embodiments to facilitate understanding of the invention and are not intended to limit the invention. Any person skilled in the art to which this invention pertains may make any modifications and variations in the form and details of the implementation without departing from the spirit and scope disclosed herein; however, the scope of patent protection for this invention shall still be determined by the scope defined in the appended claims.

Claims

1. A method for calculating the load on aircraft fasteners, characterized in that, Includes the following steps: Step 1: Calculate the stiffness of the fastener based on its effective length, diameter, and material. Fastener stiffness includes: axial stiffness, shear stiffness, torsional stiffness, and bending stiffness. Step 2: Based on the coordinate values ​​of the fastener and the coordinate values ​​of the load application point, establish a finite element model of the fastener under load using finite element software, and assign fastener properties to the finite element model of the fastener under load. Step 3: Calculate and extract the fastener load based on the boundary conditions and load conditions; Step 4: Compile all the tensile, compressive, and shear forces on the fasteners. The total tensile, compressive, and shear forces on the fasteners are the loads on the fasteners after load distribution.

2. The method for calculating aircraft fastener load according to claim 1, characterized in that, Step 1 includes: The axial stiffness of the fastener is calculated based on its effective length, diameter, and material parameters. shear stiffness and Torsional stiffness Bending stiffness and They are respectively: ； ； ； ； ； ； In the formula, The elastic modulus of the fastener material. Let this be the cross-sectional area of ​​the fastener. The effective length of the fastener. For the polar moment of inertia of the fastener, Let the moment of inertia of the fastener section be , This represents the equivalent area of ​​the fastener. Let be a constant, take , This is the shear modulus of the fastener material.

3. The method for calculating aircraft fastener load according to claim 1, characterized in that, Step 2 involves using finite element software to establish a finite element model of the fastener under load, including: Based on the coordinate values ​​of the fastener and the coordinate values ​​of the load application point, fastener nodes and load application nodes are established respectively. Heavy nodes are established at the positions of each fastener node. Fastener nodes and heavy nodes with the same position are connected to establish spring element CELAS2. Based on the fact that the fastener has 6 stiffnesses, each heavy node has 6 spring elements CELAS2. With the load application node (1001) as the master node and the fastener node as the slave node, rigid body element RBE2 is established.

4. The method for calculating aircraft fastener load according to claim 3, characterized in that, Step 2 involves assigning fastener properties to the fastener load-sharing finite element model, including: In the finite element software, assign axial stiffness, shear stiffness, torsional stiffness, and bending stiffness properties to the spring element CELAS2.

5. The method for calculating aircraft fastener load according to claim 1, characterized in that, Step 3 includes: Based on the boundary conditions of the actual structure, constrain the corresponding degrees of freedom of the fastener heavy nodes in the spring element CELAS2, apply loads to the main nodes of the RBE2 element according to the actual load conditions, and calculate and extract the fastener loads.

6. The method for calculating aircraft fastener load according to any one of claims 1 to 5, characterized in that, The aircraft structure is a fuselage pylon front connector, and the fasteners used on the fuselage pylon front connector are bolts; the fuselage pylon front connector material is 7050 aluminum alloy, the fastener material is 30CrMnSiA, and the elastic modulus of the fastener material is... shear modulus ; Step 2, which involves establishing the finite element model of the fastener, includes: Step 21: Obtain the fastener coordinate values ​​based on the fastener digital model, establish fastener nodes in the finite element software based on each coordinate value, and obtain the coordinate values ​​of the fastener load application point, and establish load application nodes in the finite element software. Step 22: Establish heavy nodes at each fastener node position, connect fastener nodes and heavy nodes with the same position to establish spring element CELAS2. Based on the fact that the fastener has 6 stiffnesses, each heavy node has 6 spring elements CELAS2; with the load-acting node (1001) as the master node and the fastener node as the slave node, establish rigid body element RBE2.

7. The method for calculating aircraft fastener load according to claim 6, characterized in that, Step 2 involves assigning fastener properties to the fastener load-sharing finite element model, including: Based on the fastener direction in the actual structure, the spring element CELAS2 is given axial stiffness, shear stiffness, torsional stiffness and bending stiffness to ensure that the six spring elements CELAS2 at the heavy nodes can realistically simulate the fastener stiffness.

8. The method for calculating aircraft fastener load according to claim 7, characterized in that, Step 4 includes: By summing the tensile, compressive, and shear forces acting on the spring element CELAS2 at the same node position, the total tensile, compressive, and shear forces acting on the spring element CELAS2 are obtained as the load on each fastener after load distribution.

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