A method for constructing a flexible connection unit for simulating rivet connection

Abstract

The present application belongs to the field of aircraft strength test, and particularly relates to a method for constructing a flexible connection unit for simulating rivet connection. The method comprises: step S1, based on the shear test of rivets, determining a first mapping table of the relationship between load and displacement of multiple test points; step S2, converting the first mapping table into a second mapping table for representing the relationship between load and stiffness; step S3, constructing a finite element model including a flexible connection unit; step S4, constructing a stiffness matrix of the flexible connection unit, and setting the initial stiffness parameters along the y-axis and the z-axis to the stiffness value corresponding to the minimum tensile load in the second mapping table; step S5, obtaining the static load applied to the finite element model, and extracting the force of the node on the flexible connection unit along the y-axis and the z-axis; step S6, interpolating the shear stiffness of the y-axis and the z-axis in the second mapping table to update the stiffness matrix. The present application can accurately simulate the stiffness of the rivet connection structure, making the simulation results more accurate.

Description

Technical Field

[0001] The present application belongs to the field of aircraft strength testing, and in particular relates to a method for constructing a flexible connection unit for simulating rivet connection. Background Art

[0002] When designing aviation structures, different connection methods must be used to connect different structural parts. The connection methods of structural parts include but are not limited to: bolts, rivets, etc. From an engineering perspective, the main function of these structural connections is to better transfer loads from one part to another.

[0003] Accurately evaluating these types of connections is crucial in simulations, as they are often stress concentration points and their presence increases the weight of the entire structure, so the number of rivets must be minimized while maintaining structural strength.

[0004] When performing finite element modeling of aviation structures, it is generally necessary to use connection units to simulate rivet connections. There are two traditional connection unit methods: one is to simulate through rigid body elements, simulating rivets as completely rigid connections; the other is to simulate through units such as Bush, and the connection stiffness is generally obtained through theoretical calculations. The simulation accuracy of the above two methods has a certain error compared with the actual structure. Summary of the invention

[0005] In order to solve at least one of the above technical problems, the present application provides a method for constructing a flexible connection unit for simulating rivet connection, which applies the rivet stiffness obtained from test data to the connection stiffness simulation of the finite element model, providing support for finite element modeling and simulation of aviation structures.

[0006] The method for constructing a flexible connection unit for simulating rivet connection provided in the present application mainly includes:

[0007] Step S1, determining a first mapping table of the relationship between load and displacement of a plurality of test points based on a shear test on the rivet;

[0008] Step S2, calculating the stiffness according to the load and displacement of each test point, thereby converting the first mapping table into a second mapping table for representing the relationship between load and stiffness;

[0009] Step S3, constructing a finite element model including a flexible connection unit, the flexible connection unit is set between node A and node B, and constructing a local coordinate system based on the flexible connection unit, the origin of the local coordinate system is located at one of the nodes of the flexible connection unit, the x-axis extends along the direction of the line connecting the two nodes, and the y-axis and the z-axis are perpendicular to the x-axis;

[0010] Step S4, constructing a flexible connection unit stiffness matrix, wherein the flexible connection unit stiffness matrix includes six-degree-of-freedom stiffness parameters, wherein the initial stiffness parameters along the y-axis and the z-axis are set to the stiffness values ​​corresponding to the minimum tensile load in the second mapping table, and other stiffness parameters are given according to the rivet structure and material parameters;

[0011] Step S5, obtaining the static load applied to the finite element model, and extracting the force of the node A on the flexible connection unit along the y-axis and the z-axis;

[0012] Step S6: interpolate the shear stiffness of the y-axis and the z-axis in the second mapping table according to the forces along the y-axis and the z-axis, respectively, to update the stiffness matrix of the flexible connection unit.

[0013] Preferably, step S1 further comprises:

[0014] Connect the two test pieces by rivets;

[0015] Reverse tensile tests are applied to the two test pieces to shear the rivets, thereby obtaining tensile loads and corresponding displacement values ​​at multiple test points, thereby constructing the first mapping table.

[0016] Preferably, in step S2, the stiffness is calculated by the following formula:

[0017] k i = p i / δ i ;

[0018] in, k i For the i The stiffness of the test points, p i For the i The load at each test point, δ i For the i The displacement of the test points.

[0019] Preferably, in step S4, other stiffness parameters are given by the following formula:

[0020] Stiffness parameter along the x-axis K x Equal to the tensile stiffness of the rivet K ls :

[0021] K x = K ls = EA / L ;

[0022] in: E is the elastic modulus of the material, A is the cross-sectional area of ​​the rivet, L is the effective length of the rivet;

[0023] Rotational stiffness parameter along the x-axis K θx Equal to the torsional stiffness of the rivet K nz :

[0024] K θx = K nz = GJ / L ;

[0025] in: G is the shear modulus of the material, J is the polar moment of inertia of the rivet section;

[0026] Rotational stiffness along the y-axis K θy Equal to the bending stiffness of the rivet K y_wq :

[0027] K θy = K y_wq = EI / L ;

[0028] in, I is the moment of inertia of the rivet section;

[0029] Rotational stiffness along the z-axis K θz Equal to the bending stiffness of the rivet K z_wq :

[0030] K θz = K z_wq = EI / L .

[0031] Preferably, in step S4, the flexible connection unit stiffness matrix is ​​a diagonal matrix.

[0032] Preferably, in step S6, the stiffness parameter of the y-axis is interpolated by the following formula: K y_new :

[0033] K y_new =K y_jq_new =[ki+1 (F y -p i )+k i (p i+1 -F y )] / (p i+1 -p i ) ;

[0034] The stiffness parameter of the z-axis is interpolated by the following formula: K z_new :

[0035] K z_new =K z_jq_new =[k i+1 (F z -p i )+k i (p i+1 -F z )] / (p i+1 -p i ) ;

[0036] in, K y_jq_new is the interpolated shear stiffness along the y-axis, K z_jq_new is the interpolated shear stiffness along the z-axis, F y is the force along the y-axis, F z is the force along the z-axis, k i For the i The stiffness of the test points, p i For the i The load at each test point, k i+1 For the i+1 The stiffness of the test points, p i+1 For the i+1 The load at each test point.

[0037] The present application can apply the rivet stiffness obtained from the test data to the connection stiffness simulation. The present application can accurately simulate the stiffness of connection structures such as rivets in the finite element simulation, making the simulation results more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a flow chart of a preferred embodiment of the method for constructing a flexible connection unit for simulating rivet connection of the present application.

[0039] Figure 2 It is a schematic diagram of a flexible connection unit.

[0040] Figure 3 is a schematic diagram of the initial stiffness matrix.

[0041] Figure 4 is a schematic diagram of the updated stiffness matrix. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical scheme and advantages of the implementation of this application clearer, the technical scheme in the implementation of this application will be described in more detail in combination with the drawings in the implementation of this application. In the drawings, the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The described implementation is a part of the implementation of this application, not all of the implementations. The implementation described below with reference to the drawings is exemplary and is intended to be used to explain this application, and cannot be understood as a limitation on this application. Based on the implementation in this application, all other implementations obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application. The implementation of this application is described in detail below in combination with the drawings.

[0043] The present application provides a method for constructing a flexible connection unit for simulating rivet connection, such as Figure 1 As shown, it mainly includes:

[0044] Step S1: Based on a shear test on a rivet, a first mapping table of the relationship between load and displacement of a plurality of test points is determined.

[0045] In some optional implementations, step S1 further includes:

[0046] Connect the two test pieces by rivets;

[0047] Reverse tensile tests are applied to the two test pieces to shear the rivets, thereby obtaining tensile loads and corresponding displacement values ​​at multiple test points, thereby constructing the first mapping table.

[0048] In this embodiment, the first mapping table constructed is shown in Table 1 below. In Table 1, pi For the i The load at each test point, δ i For the i The displacement of the test points.

[0049] Table 1 First mapping table

[0050]

[0051] Step S2: Calculate the stiffness according to the load and displacement of each test point, thereby converting the first mapping table into a second mapping table for representing the relationship between load and stiffness.

[0052] In some optional embodiments, in step S2, the stiffness is calculated by the following formula:

[0053] k i = p i / δ i ;

[0054] in, k i For the i The stiffness of the test points.

[0055] In this embodiment, the constructed second mapping table is shown in Table 2 below.

[0056] Table 2 Second mapping table

[0057]

[0058] A finite element model including a flexible connection unit is constructed. The flexible connection unit is set between node A and node B, and a local coordinate system is constructed based on the flexible connection unit. The origin of the local coordinate system is located at one of the nodes of the flexible connection unit, the x-axis extends along the direction of the line connecting the two nodes, and the y-axis and the z-axis are both perpendicular to the x-axis.

[0059] In this embodiment, the constructed finite element model is as follows Figure 2 As shown, the flexible connection unit connects node A and node B; the origin of the local coordinate system of the flexible connection unit is at node A, the x-axis direction of the local coordinate system is consistent with the direction of the AB line, and the y-axis and z-axis are perpendicular to the AB line.

[0060] Step S4, constructing a flexible connection unit stiffness matrix, wherein the flexible connection unit stiffness matrix includes six-degree-of-freedom stiffness parameters, wherein the initial stiffness parameters along the y-axis and the z-axis are set to the stiffness values ​​corresponding to the minimum tensile load in the second mapping table, and other stiffness parameters are given according to the rivet structure and material parameters.

[0061] In this embodiment, the initial stiffness parameter along the y-axis direction is K y Equal to the initial shear stiffness of the flexible link element K y_jq , which is equal to k 1 ,Right now:

[0062] K y = K y_jq = k 1 .

[0063] Similarly, the initial stiffness parameter along the z-axis is K z Equal to the initial shear stiffness of the flexible link element K z_jq , which is also equal to k 1 ,Right now:

[0064] K z = K z_jq = k 1 .

[0065] Except for these two stiffness parameters which will subsequently change with the change of load input, the stiffness parameters of the other four degrees of freedom are fixed values. In some optional implementations, in step S4, the other stiffness parameters are given by the following formula:

[0066] Stiffness parameter along the x-axis K x Equal to the tensile stiffness of the rivet K ls :

[0067] K x = K ls = EA / L ;

[0068] in: E is the elastic modulus of the material, A is the cross-sectional area of ​​the rivet, L is the effective length of the rivet;

[0069] Rotational stiffness parameter along the x-axis K θx Equal to the torsional stiffness of the rivet K nz :

[0070] K θx = K nz = GJ / L ;

[0071] in: G is the shear modulus of the material, J is the polar moment of inertia of the rivet section;

[0072] Rotational stiffness along the y-axis K θy Equal to the bending stiffness of the rivet K y_wq :

[0073] K θy = K y_wq = EI / L ;

[0074] in, I is the moment of inertia of the rivet section;

[0075] Rotational stiffness along the z-axis K θz Equal to the bending stiffness of the rivet K z_wq :

[0076] K θz = K z_wq = EI / L .

[0077] In some optional implementations, in step S4, the flexible connection unit stiffness matrix is ​​a diagonal matrix.

[0078] In this embodiment, the initial stiffness matrix K c The diagonal matrix of Figure 3 shown.

[0079] Step S5, obtaining the static load applied to the finite element model, and extracting the force of the node A on the flexible connection unit along the y-axis and the z-axis.

[0080] Step S6: interpolate the shear stiffness of the y-axis and the z-axis in the second mapping table according to the forces along the y-axis and the z-axis, respectively, to update the stiffness matrix of the flexible connection unit.

[0081] In some optional embodiments, in step S6, the stiffness parameter of the y-axis is interpolated by the following formula: K y_new :

[0082] Ky_new =K y_jq_new =[k i+1 (F y -p i )+k i (p i+1 -F y )] / (p i+1 -p i ) ;

[0083] The stiffness parameter of the z-axis is interpolated by the following formula: K z_new :

[0084] K z_new =K z_jq_new =[k i+1 (F z -p i )+k i (p i+1 -F z )] / (p i+1 -p i ) ;

[0085] in, K y_jq_new is the interpolated shear stiffness along the y-axis, K z_jq_new is the interpolated shear stiffness along the z-axis, F y is the force along the y-axis, F z is the force along the z-axis, k i For the i The stiffness of the test points, p i For the i The load at each test point, k i+1 For the i+1 The stiffness of the test points, p i+1 For the i+1 The load at each test point.

[0086] use K y_new , K z_new Initial stiffness matrix for flexible link elements K c The initial stiffness parameter in K y , K z Replace and form a new element stiffness matrix K c_new like Figure 4 shown.

[0087] The flexible connection unit constructed based on the above method is used in aircraft structure simulation, which improves the simulation accuracy.

[0088] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A method for constructing a flexible connection unit for simulating rivet connection, characterized in that: include: Step S1, determining a first mapping table of the relationship between load and displacement of a plurality of test points based on a shear test on the rivet; Step S2, calculating the stiffness according to the load and displacement of each test point, thereby converting the first mapping table into a second mapping table for representing the relationship between load and stiffness; Step S3, constructing a finite element model including a flexible connection unit, the flexible connection unit is set between node A and node B, and constructing a local coordinate system based on the flexible connection unit, the origin of the local coordinate system is located at one of the nodes of the flexible connection unit, the x-axis extends along the direction of the line connecting the two nodes, and the y-axis and the z-axis are perpendicular to the x-axis; Step S4, constructing a flexible connection unit stiffness matrix, wherein the flexible connection unit stiffness matrix includes six-degree-of-freedom stiffness parameters, wherein the initial stiffness parameters along the y-axis and the z-axis are set to the stiffness values ​​corresponding to the minimum tensile load in the second mapping table, and other stiffness parameters are given according to the rivet structure and material parameters; Step S5, obtaining the static load applied to the finite element model, and extracting the force of the node A on the flexible connection unit along the y-axis and the z-axis; Step S6, interpolating the shear stiffness of the y-axis and the z-axis in the second mapping table according to the forces along the y-axis and the z-axis, respectively, to update the stiffness matrix of the flexible connection unit; Among them, in step S4, other stiffness parameters are given by the following formula: Stiffness parameter K along the x-axis x Equal to the tensile stiffness K of the rivet ls : K x =K ls =EA / L; Where: E is the elastic modulus of the material, A is the cross-sectional area of ​​the rivet, and L is the effective length of the rivet; The rotational stiffness parameter K along the x-axis θx Equal to the torsional stiffness K of the rivet nz : K θx =K nz =GJ / L; Where: G is the shear modulus of the material, J is the polar moment of inertia of the rivet section; The rotational stiffness K along the y-axis θy Equal to the bending stiffness K of the rivet y_wq : K θy =K y_wq =NO / L; Where I is the moment of inertia of the rivet section; Rotational stiffness K along the z-axis θz Equal to the bending stiffness K of the rivet z_wq : K θz =K z_wq = NO / L.

2. The method for constructing a flexible connection unit for simulating rivet connection according to claim 1, characterized in that: Step S1 further comprises: Connect the two test pieces by rivets; Reverse tensile tests are applied to the two test pieces to shear the rivets, thereby obtaining tensile loads and corresponding displacement values ​​at multiple test points, thereby constructing the first mapping table.

3. The method for constructing a flexible connection unit for simulating rivet connection according to claim 1, characterized in that: In step S2, the stiffness is calculated by the following formula: k i =p i / d i ; Among them, k i is the stiffness of the ith test point, p i is the load of the i-th test point, δ i is the displacement of the ith test point.

4. The method for constructing a flexible connection unit for simulating rivet connection according to claim 1, characterized in that: In step S4, the flexible connection unit stiffness matrix is ​​a diagonal matrix.

5. The method for constructing a flexible connection unit for simulating rivet connection according to claim 1, characterized in that: In step S6, the stiffness parameter K of the y-axis is interpolated by the following formula: y_new : K y_new =K y_jq_new =[k i+1 (F y -p i )+k i (p i+1 -F y )] / (p i+1 -p i ); The z-axis stiffness parameter K is interpolated by the following formula: z_new : K z_new =K z_jq_new =[k i+1 (F z -p i )+k i (p i+1 -F z )] / (p i+1 -p i ); Among them, K y_jq_new is the interpolated shear stiffness along the y-axis, K z_jq_new is the interpolated shear stiffness along the z-axis, F y is the force along the y-axis, F z is the force along the z axis, k i is the stiffness of the ith test point, p i is the load of the ith test point, k i+1 is the stiffness of the i+1th test point, p i+1 is the load at the i+1th test point.

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