A method for determining the quasi-strength of fairing notch bolts

Abstract

The present invention discloses a method for determining the quasi-strength of a fairing notch bolt, comprising: determining a finite element model of tensile stiffness of the notch bolt; extracting the tensile stiffness of the notch bolts on the separation surface of two half fairings; establishing a finite element model of the fairing including a column section and a cone section; replacing the longitudinal separation mechanism with a spring unit having a certain spring unit stiffness value to determine the fairing bearing capacity and the connection strength of the notch bolt. In the fairing model, the present invention replaces the complex longitudinal separation mechanism with only a spring unit corresponding to the tensile stiffness, and simplifies the model with millions of degrees of freedom into a model with tens of thousands of degrees of freedom to determine the fairing bearing capacity and the connection strength of the notch bolt.

Description

Technical Field

[0001] The invention belongs to the technical field of overall design and strength analysis of aerospace structures, and relates to a method for determining the quasi-strength of a fairing notch bolt. Background Art

[0002] The fairing is composed of two half fairings connected together by a longitudinal separation mechanism. When the fairing is longitudinally separated, the explosive column in the flat tube is detonated, the flat tube expands, and the notched bolts are broken to realize the longitudinal separation of the separation mechanism.

[0003] The longitudinal separation mechanism is distributed on the butt joint surface of the two halves of the fairing, and is composed of flat tubes, notch bolts, longitudinal butt joint beams, brackets and other structures, among which the number of notch bolts is as high as hundreds. Before the fairing is separated, the longitudinal separation mechanism (the main load-bearing component is the notch bolt) mainly bears the tensile force along the length direction of the notch bolt generated by the axial pressure, bending moment, and internal pressure load of the fairing. The force on the notch bolt is closely related to the tensile stiffness of the local longitudinal separation mechanism along the circumferential direction of the fairing. Considering the complex structure of the longitudinal separation mechanism and the large number of notch bolts, it is very difficult and unrealistic to build all of them and consider the contact relationship between the components during modeling.

[0004] At present, there is no simple and feasible method to check the strength of notched bolts at home and abroad. Summary of the invention

[0005] The technical problems solved by the present invention are:

[0006] Aiming at the problem that the longitudinal docking structure of the fairing and the local connection structure of the notch bolts are complex and unanalyzable, a method for determining the quasi-strength of the notch bolts of the fairing is proposed. By establishing a finite element model of the local area structure of the notch bolts, the tensile stiffness of the local area where a single notch bolt is located is extracted. In the fairing model, the complex longitudinal separation mechanism is replaced by only the spring unit corresponding to the tensile stiffness, and the model with millions of degrees of freedom is simplified to a model with tens of thousands of degrees of freedom, so as to determine the bearing capacity of the fairing and the connection strength of the notch bolts.

[0007] Technical solution of the present invention:

[0008] A method for determining the quasi-strength of a fairing notch bolt, comprising:

[0009] Determine the finite element model of tensile stiffness of the notch bolt: The finite element model of tensile stiffness of the notch bolt includes a bracket, a notch bolt, a flat tube and a docking truss, and the notch bolt is provided with a groove circumferentially on the screw rod; the fairing is two symmetrical half-covers, each half-cover includes a cone section and a column section, and the two docking trusses are respectively fixedly connected to the two half-covers of the fairing, and the two docking trusses are fixedly connected by a plurality of notch bolts to realize the connection of the two fairings on the longitudinal separation surface; the bracket and the flat tube are sequentially arranged close to the bolt head;

[0010] Extract the tensile stiffness of the notch bolts on the separation surface of the two half fairings: apply a tensile load on the notch bolts to determine the tensile stiffness of the notch bolts, including the tensile stiffness K1 of the notch bolts on the cone section closest to the cone-column joint surface, the tensile stiffness K2 of the notch bolts on the column section closest to the cone-column joint surface, the tensile stiffness K3 of the notch bolts with consistent spacing on the cone section, and the tensile stiffness K4 of the notch bolts with consistent spacing on the column section;

[0011] A finite element model of the fairing including the column section and the cone section was established: the lower end of the column section and the upper end of the cone section were constrained, and the flight load of the fairing was applied. The axial pressure, bending moment and shear loads were applied to the upper end of the cone section, and the internal pressure was applied to the inner wall of the cone section and the column section. The bracket, notch bolts, flat tubes and docking trusses constituted a longitudinal separation mechanism, which was simulated by spring units. The stiffness values ​​of the spring units included the tensile stiffness K1 of the notch bolts on the cone section closest to the cone-column docking surface, the tensile stiffness K2 of the notch bolts on the column section closest to the cone-column docking surface, the tensile stiffness K3 of the notch bolts with consistent spacing on the cone section, and the tensile stiffness K4 of the notch bolts with consistent spacing on the column section.

[0012] The longitudinal separation mechanism is replaced by a spring unit having a certain spring unit stiffness value to determine the fairing load-bearing capacity and the connection strength of the notch bolts.

[0013] Furthermore, through the expansion of the flat tube on the docking beam and the bracket, a plurality of notch bolts are pulled off at the notches, thereby achieving separation of the two half fairings.

[0014] Furthermore, the two half fairings are separated on a plane parallel to the symmetry axis.

[0015] Furthermore, in the finite element model of the fairing, the spacing between the notched bolts is half of the actual spacing between two adjacent bolt heads or the distance from the bolt head to the conical column butt joint surface.

[0016] Furthermore, in the finite element model of the fairing, the cone section and column section are simulated by shell elements, and the longitudinal butt girder is simulated by beam elements.

[0017] Furthermore, in the finite element model of the fairing, the docking girders and bracket models are simulated by solid elements C3D8I, and the flat tube model is simulated by shell elements S4.

[0018] Furthermore, in the finite element model of the fairing, the bracket, the flat tube and the docking beam are connected through a contact relationship, and the friction coefficient at the connection is 0.1.

[0019] Furthermore, in the finite element model of the fairing, the docking beam and the bracket are meshed.

[0020] Furthermore, the number of circumferential units of the flat tube is not less than 12, and the sizes of the docking beam and the bracket unit are consistent with those of the flat tube.

[0021] Furthermore, the unit size is 10 to 20 mm.

[0022] The beneficial effects of the present invention compared with the prior art are:

[0023] (1) The present invention establishes a finite element model of the local area structure of the notch bolt to obtain the tensile stiffness of the local area of ​​a single notch bolt along the length direction of the bolt. In the whole cover model, the notch bolt is simulated by a spring unit, and the tensile stiffness is used as the stiffness of the spring unit. The tensile force on the notch bolt can be calculated;

[0024] (2) The present invention simplifies the notched bolts into spring units, thereby ignoring components such as partial brackets, notched bolts, flat tubes, and longitudinal butt girders, thereby simplifying a model with millions of degrees of freedom into a model with tens of thousands of degrees of freedom, reducing the calculation time from 7 to 8 days to 2 to 3 hours, greatly reducing the calculation scale and improving the calculation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a diagram showing the connection relationship between the longitudinal separation mechanism and the half cover;

[0026] Among them, 1- fairing; 2- docking beam; 3- longitudinal separation mechanism; 4- bracket; 5- longitudinal separation surface; 6- flat tube; 7- notch bolt;

[0027] Figure 2 Cross-sectional view of the model for calculating the stiffness of the notched bolt;

[0028] Figure 3 is the finite element model and loading diagram;

[0029] Among them, 5-longitudinal separation plane; 8-cone section; 9-column section;

[0030] Figure 4 The schematic diagram of bolt position;

[0031] Among them, 10-notch bolts on the cone section closest to the cone-column joint surface, 11-notch bolts on the column section closest to the cone-column joint surface, 14-notch bolts with consistent spacing on the cone section, 12-notch bolts with consistent spacing on the column section;

[0032] Figure 5 is the finite element model of tensile stiffness of notched bolt;

[0033] Figure 6 is the X-direction displacement distribution of the finite element model of the notched bolt tensile steel;

[0034] Figure 7Finite element model for strength analysis of notched bolt structures;

[0035] Figure 8 This is an enlarged finite element model of the local area where the notched bolt is located.

[0036] Among them 13-spring unit. DETAILED DESCRIPTION

[0037] The present invention will be further described below in conjunction with the embodiments.

[0038] A method for determining the quasi-strength of a fairing notch bolt, comprising:

[0039] Determine the finite element model for the tensile stiffness of the notched bolt, such as Figure 1 As shown, the finite element model of the tensile stiffness of the notch bolt includes a bracket, a notch bolt, a flat tube and a docking truss, and the notch bolt has a groove circumferentially arranged on the screw rod; the fairing 1 is composed of two symmetrical half-covers, each half-cover includes a cone section and a column section, and two docking trusses 2 are respectively fixedly connected to the two half-covers of the fairing, and the two docking trusses are fixedly connected by a plurality of notch bolts to realize the connection of the two fairings at the longitudinal separation surface 5; the bracket 4 and the flat tube 6 are sequentially arranged close to the bolt head;

[0040] Extract the tensile stiffness of the notch bolts 7 on the separation surface of the two half fairings: Apply a tensile load on the notch bolts, such as Figure 2 As shown, the tensile stiffness of the notch bolts is determined, including the tensile stiffness K1 of the notch bolts on the cone section closest to the cone-column joint surface, the tensile stiffness K2 of the notch bolts on the column section closest to the cone-column joint surface, the tensile stiffness K3 of the notch bolts with uniform spacing on the cone section, and the tensile stiffness K4 of the notch bolts with uniform spacing on the column section;

[0041] like Figure 3-8 As shown, a finite element model of the fairing including the column section and the cone section is established: the lower end of the column section and the upper end of the cone section are constrained, and the flight condition load of the fairing is applied, and the axial pressure, bending moment, and shear loads are applied to the upper end of the cone section. The internal pressure acts on the inner walls of the cone section 8 and the column section 9. The bracket, the notch bolts, the flat tube, and the docking truss constitute a longitudinal separation mechanism, which is simulated by a spring unit. The spring unit stiffness value includes the tensile stiffness K1 of the notch bolt 10 on the cone section closest to the cone-column docking surface, the tensile stiffness K2 of the notch bolt 11 on the column section closest to the cone-column docking surface, the tensile stiffness K3 of the notch bolts 14 with consistent spacing on the cone section, and the tensile stiffness K4 of the notch bolts 12 with consistent spacing on the column section;

[0042] The longitudinal separation mechanism 3 is replaced by a spring unit 13 having a certain spring unit stiffness value to determine the fairing load-bearing capacity and the connection strength of the notch bolts.

[0043] Through the expansion of the flat tube on the docking beam and the bracket, a plurality of notch bolts are pulled off at the notches, so that the two half-covers of the fairing are separated, and the two half-covers of the fairing are separated on a plane parallel to the symmetry axis.

[0044] In the finite element model of the fairing, the spacing between the notched bolts is half of the actual spacing between two adjacent bolt heads or the distance from the bolt head to the conical column joint surface.

[0045] In the finite element model of the fairing, the cone and column sections are simulated by shell elements, and the longitudinal butt girder is simulated by beam elements. In the finite element model of the fairing, the butt girder and bracket models are simulated by solid elements C3D8I, and the flat tube model is simulated by shell elements S4. In the finite element model of the fairing, the bracket, flat tube and butt girder are connected by contact relationship, and the friction coefficient at the connection is 0.1. The butt girder and bracket are meshed. The number of circumferential units of the flat tube is not less than 12, and the unit size of the butt girder and bracket is consistent with that of the flat tube. The unit size is 10 to 20 mm.

[0046] Example

[0047] Determine the stiffness of the notch bolt. Calculate the simplified model and extract the stiffness of the notch bolt.

[0048] For the establishment of the simplified model, the conical section and the notch bolt above the cylindrical joint surface are selected as an example. The first notch bolt at this position is 114mm away from the free end and 80mm away from the second notch bolt. The spacing of all other notch bolts is 80mm. Figure 5 Due to the large difference in spacing distribution, the tensile stiffness of the first notch bolt is different from that of the others. Therefore, two models are established to simulate the tensile stiffness of the two types of bolts respectively.

[0049] The finite element model for calculating the tensile stiffness of the first notch bolt is shown in Figure 6. In this model, the flat tube and longitudinal butt girders are simulated by shell element S4, and the bracket is simulated by body element C3D8I, and contact relationships are established between the components. The length of all components is 154mm, and the distance between the first notch bolt and the free edge is 114mm + half of the distance between the first notch bolt and the second notch bolt, which is 80mm. The upper end face of the model is symmetrically constrained, and the lower end face is free. The butt girders are "U"-shaped shells, and the two shell element edges at the U-shaped opening end are fixedly constrained. The material mode of the flat tube is the elastic-plastic bilinear hardening mode. Its material is 1Cr18Ni9Ti, the elastic stage modulus is 180GPa, the plastic stage modulus is 0.9GPa, and the yield strength is 180MPa; the materials of other components are all aluminum, and the linear elastic mode is adopted, with an elastic modulus of 70GPa. The loading horizontally to the left is 8000N, which is the breaking tension of the notch bolt, and the position is 40mm away from the upper symmetrical constraint surface. The deformation at the loading point (notch bolt) is 0.5mm. Therefore, the tensile stiffness of the first notch bolt is 8000 / 5e-4 (N / m), which is 1.6e7 (N / m).

[0050] The modeling method for simulating the stiffness of other notched bolts is basically the same as the first one, except that the model length is 80 mm, the bolt is located in the middle of the model, and the upper and lower ends are symmetrically constrained. The calculation results show that the tensile stiffness is: 8000 / 8.3e-4 (N / m), that is, 9.64e6 (N / m).

[0051] A finite element analysis model of notch bolt strength was established.

[0052] The finite element model of the column and cone sections of the fairing is established. The lower end of the column section is fixed and constrained, and the upper end of the cone section is coupled through a rigid surface. The axial bending shear load is applied at the coupling point, and the internal pressure load is applied to the inner wall of the shell. In the model, the cone section and column section are simulated by shell elements, and the longitudinal butt truss is simulated by beam elements. The notched bolt and its local structure are simulated by spring elements. The spring element stiffness is K. The finite element model is shown in Figure 7 , 8 The geometric parameters and material properties of the beam and shell elements that simulate other components are consistent with the actual structure. The stress of the notched bolt can be obtained by calculating the model.

[0053] The present invention establishes a finite element model of the local area structure of the notch bolt to obtain the tensile stiffness of the local area of ​​a single notch bolt along the length direction of the bolt. The notch bolt is simulated by a spring unit in the whole cover model, and the tensile stiffness is used as the stiffness of the spring unit to calculate the tensile force on the notch bolt.

[0054] The present invention simplifies the notched bolts into spring units, thereby ignoring components such as partial brackets, notched bolts, flat tubes, and longitudinal butt girders, thereby simplifying a model with millions of degrees of freedom into a model with tens of thousands of degrees of freedom, reducing the calculation time from 7 to 8 days to 2 to 3 hours, greatly reducing the calculation scale and improving the calculation efficiency.

[0055] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for determining the quasi-strength of a fairing notch bolt, characterized in that: include: Determine the finite element model of tensile stiffness of the notch bolt: The finite element model of tensile stiffness of the notch bolt includes a bracket, a notch bolt, a flat tube and a docking truss, and the notch bolt is provided with a groove circumferentially on the screw rod; the fairing is two symmetrical half-covers, each half-cover includes a cone section and a column section, and the two docking trusses are respectively fixedly connected to the two half-covers of the fairing, and the two docking trusses are fixedly connected by a plurality of notch bolts to realize the connection of the two fairings on the longitudinal separation surface; the bracket and the flat tube are sequentially arranged close to the bolt head; Extract the tensile stiffness of the notch bolts on the separation surface of the two half fairings: determine the simplified model for stiffness calculation for each type of notch bolts, apply a tensile load to the notch bolts of each simplified model, and determine the tensile stiffness of the notch bolts on the longitudinal separation surface, including the tensile stiffness K1 of the notch bolts on the cone section closest to the cone-column joint surface, the tensile stiffness K2 of the notch bolts on the column section closest to the cone-column joint surface, the tensile stiffness K3 of the notch bolts with consistent spacing on the cone section, and the tensile stiffness K4 of the notch bolts with consistent spacing on the column section; A finite element model of a fairing including a column section and a cone section is established: the lower end of the column section and the upper end of the cone section are constrained, and the flight load of the fairing is applied. The axial pressure, bending moment, and shear loads are applied to the upper end of the cone section, and the internal pressure is applied to the inner walls of the cone section and the column section. The bracket, the notch bolts, the flat tube, and the docking truss constitute a longitudinal separation mechanism. The notch bolts are simulated by spring units. The stiffness values ​​of the spring units include the tensile stiffness K1 of the notch bolts on the cone section closest to the cone-column docking surface, the tensile stiffness K2 of the notch bolts on the column section closest to the cone-column docking surface, the tensile stiffness K3 of the notch bolts with consistent spacing on the cone section, and the tensile stiffness K4 of the notch bolts with consistent spacing on the column section. The finite element model of the fairing including the column section and the cone section is established to determine the bearing capacity of the fairing and the connection strength of the notch bolts.

2. A method for determining the quasi-strength of a fairing notch bolt according to claim 1, characterized in that: The expansion of the flat tube acts on the docking beam and the bracket, and multiple notched bolts are pulled off at the notches, thereby achieving separation of the two half-covers of the fairing.

3. A method for determining the quasi-strength of a fairing notch bolt according to claim 1, characterized in that: The two half fairings are separated on a plane parallel to the axis of symmetry.

4. A method for determining the quasi-strength of a fairing notch bolt according to claim 1, characterized in that: In the finite element model of the fairing including column section and cone section, the spacing between the notched bolts is half of the spacing between two actual adjacent bolt heads or the distance from the bolt head to the butt surface of the cone column.

5. A method for determining the quasi-strength of a fairing notch bolt according to claim 1, characterized in that: In the finite element model of the fairing including column and cone sections, the cone and column sections are simulated by shell elements, and the longitudinal butt girders are simulated by beam elements.

6. A method for determining the quasi-strength of a fairing notch bolt according to claim 1, characterized in that: In the finite element model of the fairing including column and cone sections, the docking truss and bracket models are simulated by solid elements C3D8I, and the flat tube model is simulated by shell elements S4.

7. A method for determining the quasi-strength of a fairing notch bolt according to claim 1, characterized in that: In the finite element model of the fairing including column segments and cone segments, the bracket, flat tube and docking truss are connected through contact relationship, and the friction coefficient at the connection is 0.

1.

8. A method for determining the quasi-strength of a fairing notch bolt according to claim 1, characterized in that: In the finite element model of the fairing including column and cone sections, meshing of the butt girders and brackets is performed.

9. A method for determining the quasi-strength of a fairing notch bolt according to claim 8, characterized in that: The number of circumferential units of the flat tube shall not be less than 12, and the sizes of the docking beam and bracket units shall be consistent with those of the flat tube.

10. A method for determining the quasi-strength of a fairing notch bolt according to claim 9, characterized in that: The unit size is 10~20mm.

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