A method for checking the preload force of ultra-deep cold dissimilar metal connection bolts based on simplified modeling

Abstract

The present invention discloses a method for checking the preload force of ultra-deep cold dissimilar metal connection bolts based on simplified modeling, including: defining bolt structural parameters; defining structural parameters of dissimilar metal connected parts; defining mechanical parameters and thermophysical parameters of bolt and connected parts materials; equivalent model modeling and meshing; mechanical boundary condition loading, thermal boundary condition loading; defining contact pairs; obtaining the ultra-deep cold bolt preload force value through thermal-mechanical coupling simulation calculation and judging whether it meets the corresponding mechanical evaluation index. This scheme can use a simplified model with a small amount of calculation to perform thermal-mechanical coupling calculation without introducing stress concentration to ensure calculation convergence; this scheme fills the gap in the verification method of the preload force of dissimilar metal connection bolts under ultra-deep cold conditions, and provides an evaluation standard based on the destructive torque and the evaluation standard of the bolt tangential force and axial force, which can judge the reliability of the bolt connection.

Description

Technical Field

[0001] The invention relates to the technical field of mechanical connectors, and in particular to a method for checking the pre-tightening force of ultra-deep cold dissimilar metal connecting bolts based on simplified modeling. Background Art

[0002] In the field of superconducting magnets and cryogenic pressure vessels, dissimilar metal fasteners are generally connected with bolts under ultra-deep cold conditions. However, due to the different thermal expansion coefficients of the materials, the bolt preload will vary to varying degrees. In order to ensure the reliability of the structure, it is necessary to calibrate the preload of the ultra-deep cold dissimilar metal connection bolts.

[0003] At present, the simulation analysis of bolt preload at room temperature generally adopts two modeling methods. One is a simplified modeling method using beam elements, but this method can extract few bolt force results and has low calculation accuracy; the other is a detailed modeling method, but this method has a very large number of grids and a lot of calculations, making it difficult to apply; there is currently no verification method for the bolt preload connecting dissimilar metals under ultra-cold conditions.

[0004] Therefore, how to provide a method for checking the preload force of ultra-deep cold dissimilar metal connection bolts based on simplified modeling to ensure the reliability of the bolt connection is an urgent problem to be solved by personnel in this technical field. Summary of the invention

[0005] In view of this, the present invention provides a method for checking the preload force of ultra-deep cold dissimilar metal connection bolts based on simplified modeling to ensure the reliability of the bolt connection.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A method for checking the preload force of ultra-deep cold dissimilar metal connection bolts based on simplified modeling, comprising:

[0008] Define bolt structure parameters;

[0009] Define the structural parameters of dissimilar metal connected parts;

[0010] Define the mechanical parameters and thermophysical parameters of bolts and connected parts;

[0011] Simplify modeling and meshing;

[0012] Mechanical boundary condition loading, thermal boundary condition loading;

[0013] Define contact pairs;

[0014] The preload force of the ultra-deep cold bolt is obtained through thermal-mechanical coupling simulation calculation and it is judged whether it meets the corresponding mechanical evaluation indicators.

[0015] Preferably, in the above-mentioned ultra-deep cold dissimilar metal connection bolt preload verification method based on simplified modeling, the definition of bolt structural parameters includes:

[0016] The defined bolt structural parameters include: bolt head fastener diameter e, bolt head thickness k, nominal diameter D, bolt length lbolt and thread length lthread. The gasket structural parameters include: large gasket inner diameter d1, large gasket outer diameter d2 and large gasket thickness hwasher.

[0017] Preferably, in the above-mentioned ultra-deep cold dissimilar metal connection bolt preload verification method based on simplified modeling, the definition of the structural parameters of the dissimilar metal connected parts includes:

[0018] According to the thickness of the two connected parts in actual situations, the thickness of the first layer of connected parts is 1h1, and the thickness of the second layer of connected parts is 2h2;

[0019] The minimum size of the simplified plate length, plate width and grid unit can be further determined based on the minimum size of the bolt and gasket structure.

[0020] Define the simplified plate model with the length of the plate as length, the width of the plate as width, and the minimum size of the grid unit as gridmin. Then the following modeling conditions need to be met:

[0021]

[0022] Preferably, in the above-mentioned ultra-deep cold dissimilar metal connection bolt preload verification method based on simplified modeling, the mechanical parameters and thermophysical parameters of the bolt and the connected material are defined as follows:

[0023] The mechanical parameters include density rho, Young's modulus E, and Poisson's ratio nu; the thermophysical parameters include thermal expansion coefficient alpha, and the deformation parameters calculated from the thermal expansion coefficient are related to the mechanical parameters.

[0024] Preferably, in the above-mentioned method for checking the preload force of ultra-deep cold dissimilar metal connection bolts based on simplified modeling, the simplified modeling and meshing include:

[0025] According to the defined bolt structural parameters, structural parameters of dissimilar metal connected parts, and mechanical parameters and thermophysical parameters of the bolt and connected parts materials, a simplified model for bolt preload analysis is established and the mesh is divided.

[0026] Preferably, in the above-mentioned ultra-deep cold dissimilar metal connection bolt preload verification method based on simplified modeling, the mechanical boundary condition loading and thermal boundary condition loading include:

[0027] Mechanical boundary conditions, including the preload of bolts at room temperature and the constraints of dissimilar metal connectors;

[0028] The thermal boundary condition is the transition from room temperature to ultra-cold working temperature.

[0029] Preferably, in the above-mentioned ultra-deep cold dissimilar metal connection bolt preload verification method based on simplified modeling, the mechanical boundary conditions, including the preload of the bolt at room temperature and the constraint conditions of the dissimilar metal connector, include:

[0030] A displacement constraint method with rigid body motion suppression is used: three completely separated non-collinear points are selected, the first point is fixed in three directions, the second point is restricted in two directions of the vector normal from the first point to the second point, and the last point is restricted in the direction perpendicular to the plane formed by the three points;

[0031] Specify the z-displacement of the bottom surface of the second layer of the two connected parts to be 0.

[0032] Preferably, in the above-mentioned ultra-deep cold dissimilar metal connection bolt preload verification method based on simplified modeling, the definition of contact pairs includes:

[0033] A contact pair is established between the lower surface of the gasket and the first layer of the two connected parts, and the augmented Lagrangian method is used to perform contact simulation calculation to obtain the preload value of the ultra-deep cold bolt.

[0034] Preferably, in the above-mentioned ultra-deep cold dissimilar metal connection bolt preload verification method based on simplified modeling, the ultra-deep cold bolt preload value is obtained by thermal-mechanical coupling simulation calculation and the judgment on whether the corresponding mechanical evaluation index is met includes:

[0035] Mechanical evaluation indicators include:

[0036] Breaking torque: KF pc d <T;

[0037] Bolt tangential force: F tc <[(0.3 / 1.1)×F pc ]-[(0.24 / 1.1)×F ac ]=(0.273×F pc )-(0.218×F ac );

[0038] Bolt axial force: compression bolt F ac <F pc ;

[0039] Tension bolt F ac <F a -F pc ;

[0040] Where: K is the tightening coefficient; F pcis the low temperature preload; d is the bolt diameter; T is the bolt breaking torque; F tc is the calculated low temperature tangential force; F pc F is the low temperature preload; ac is the calculated low-temperature axial force, which is positive when under tension and negative when under compression; F a is the allowable axial force;

[0041] When bolted connections are used, the acceptance criteria in the tangential direction are given by the slip resistance, the acceptance criteria in the axial direction are given by the preload when the bolt is in compression, and by the difference between the permissible axial force and the preload when the bolt is in tension;

[0042] The calculation formula of sliding resistance is:

[0043] F sa =(k s ×n×μ×F c ) / γ,

[0044] In the formula, k s is the geometric factor, k s =1.0; n is the number of friction interfaces; μ is the slip coefficient, μ=0.3 (C-grade surface); γ is the bolt safety factor 1.1;

[0045] F c =F pc -0.8×F ac ,

[0046] When the number of friction interfaces n is 1:

[0047] F sa =[(0.3 / 1.1)×F pc ]-[(0.24 / 1.1)×F ac ]=(0.273×F pc )-(0.218×F ac );

[0048] When the number of friction interfaces n is 2:

[0049] F sa =(0.546×F pc )-(0.436×F ac ).

[0050] The present invention provides a method for checking the preload force of ultra-deep cold dissimilar metal connection bolts based on simplified modeling. The calculation amount of this scheme is between that of detailed modeling and simplified modeling, and the principle of equivalent model modeling and the minimum size of the grid that needs to be controlled are given; in addition, this scheme can use a simplified model with a smaller calculation amount to perform thermal-mechanical coupling calculation without introducing stress concentration, and ensure the convergence of the calculation; this scheme fills the gap in the method for checking the preload force of dissimilar metal connection bolts under ultra-deep cold conditions, and gives an evaluation standard based on the breaking torque and the evaluation standard of the bolt tangential force and axial force, so that the reliability of the bolt connection can be judged. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0052] Figure 1 It is an equivalent simulation diagram of the pre-tightening force verification method of ultra-deep cold dissimilar metal connection bolts based on simplified modeling disclosed in an embodiment of the present invention;

[0053] Figure 2 This is a diagram of ultra-cold preload force values ​​corresponding to different preload forces applied at room temperature disclosed in an embodiment of the present invention;

[0054] Figure 3 It is an axial force diagram of the inner and outer sides of the bolt under ultra-cold conditions when the pre-tightening force of the bolt at room temperature reaches N according to the embodiment of the present invention;

[0055] Figure 4 The present invention is a flowchart of a method for checking the preload force of ultra-deep cold dissimilar metal connecting bolts based on simplified modeling disclosed in an embodiment of the present invention. DETAILED DESCRIPTION

[0056] The invention discloses a method for checking the pre-tightening force of ultra-deep cold dissimilar metal connecting bolts based on simplified modeling to ensure the reliability of the bolt connection.

[0057] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0058] like Figure 1As shown, the present application discloses a method for checking the preload force of ultra-deep cold dissimilar metal connection bolts based on simplified modeling, which comprises the following steps:

[0059] Step S1: Define bolt structure parameters.

[0060] There are generally two ways to model bolt preload simulation analysis. One is to use the simplified modeling method of BEAM beam, but this method can extract few bolt force results and has low calculation accuracy; the other is to use detailed modeling, but this method has a very large number of grids and a large amount of calculation, making it difficult to apply.

[0061] In this application, a detailed modeling method of simplifying thread features by establishing contact pairs is used to model bolts and washers. According to the bolt and washer structure used in actual engineering situations (for example, the two connected metals are 304 stainless steel and TC4 titanium alloy, the thickness of the connected parts are 20 mm and 35 mm, the bolt and washer materials are 304 stainless steel, and the model is M12), the bolt structure parameters that need to be defined include: bolt head fastener diameter e (for example, 20 [mm]), bolt head thickness k (for example, 7.5 [mm]), bolt nominal diameter D (for example, 12 [mm]), bolt length lbolt (for example, 45 [mm]), thread length lthread (for example, 22 [mm]);

[0062] The gasket structural parameters include: large gasket inner diameter d1 (eg 13 [mm]), large gasket outer diameter d2 (eg 37 [mm]), and large gasket thickness hwasher (eg 3 [mm]).

[0063] Step S2: define structural parameters of dissimilar metal connected parts.

[0064] According to the thickness of the two connected parts connected by bolts in actual engineering situations, the thickness of the dissimilar metal connected parts during equivalent modeling can be determined first, where the first layer of connected parts: plate thickness 1h1 (for example, 20 [mm]), the second layer of connected parts: plate thickness 2h2 (for example, 35 [mm]). The dissimilar metal connected parts involved in this application are the first layer of connected parts and the second layer of connected parts having different materials.

[0065] On this basis, the minimum size of the simplified plate length, plate width and grid unit can be further determined according to the minimum size of the bolt and gasket structure. The determination of the simplified plate length, plate width and minimum grid size needs to meet two requirements. On the one hand, according to the Saint-Venant principle, a sufficiently large simplified plate model needs to be constructed to simulate the stress state of an infinitely large plate; on the other hand, according to the demand for calculations by the simplified model, the size of the equivalent plate model needs to be reduced as much as possible in order to reduce the number of grid units and thus reduce the amount of calculations. It should be noted here that the equivalent method of the first layer of connected parts and the second layer of connected parts is the same. Preferably, the first layer of connected parts and the second layer of connected parts can be simplified to the same size and shape. Specifically:

[0066] Define the simplified plate model with the length of the plate as length, the width of the plate as width, and the minimum size of the grid unit as gridmin. Then the following modeling conditions need to be met:

[0067]

[0068] In a specific embodiment, Figure 1 As shown, the length of the metal plate can be set to 100 [mm], the width of the plate can be set to 100 [mm], and the minimum size of the grid unit can be 0.3 mm.

[0069] Step S3: define the mechanical parameters and thermophysical parameters of the bolt and the connected parts.

[0070] The materials of the bolts and connected parts are defined according to the actual requirements of the project. In a specific embodiment, the bolts and gaskets may be made of 304 stainless steel, the upper connected part is TC4 titanium alloy, and the lower connected part is 304 stainless steel.

[0071] In order to conduct subsequent thermal-mechanical coupling finite element analysis, it is necessary to define the mechanical parameters and thermophysical parameters of the two connected materials related to ultra-cold temperature respectively. Specifically, the mechanical parameters include density rho, Young's modulus E, and Poisson's ratio nu; the thermophysical parameters include the thermal expansion coefficient alpha.

[0072] The material parameters of 304 stainless steel and TC4 titanium alloy are as follows. The specific parameters can be obtained by looking up the table.

[0073] In addition, the parameters in the table below correspond to the calculation formulas for different mechanical parameters and thermophysical parameters in the temperature range from room temperature to ultra-cold temperatures.

[0074]

[0075]

[0076]

[0077] Step S4: Simplify modeling and meshing.

[0078] According to the defined bolt structural parameters, structural parameters of dissimilar metal connected parts, and mechanical parameters and thermophysical parameters of bolt and connected parts materials, a simplified model for bolt preload analysis is established and the mesh is divided, and the minimum size of the mesh unit is controlled at 0.3 mm.

[0079] After the parameters defined above are used, equivalent modeling is performed. The software used can be set according to actual needs, and the size of the divided grid units can also be set according to different accuracy requirements, all within the protection range.

[0080] Step S5: Loading mechanical boundary conditions.

[0081] Mechanical boundary conditions are applied, including the preload of bolts at room temperature and the constraints of dissimilar metal connectors.

[0082] Establish the section for applying bolt preload, and the distance between the bolt end and the section position is 0.75lbolt.

[0083] In order to avoid too many displacement constraints introducing stresses that are not in line with engineering reality and to prevent the problem of non-convergence of solutions caused by insufficient displacement constraints, the constraints in this application adopt a displacement constraint method with rigid body motion suppression.

[0084] Specifically, three completely separated non-collinear points are selected (for a 3D model), the first point is fixed in three directions, the second point is restricted to the two directions of the vector normal from the first point to the second point, and the last point is restricted to the direction perpendicular to the plane formed by the three points.

[0085] In order to prevent the solution from not converging, the z-displacement of the bottom surface of the second layer of connected parts is specified to be 0.

[0086] Specifically, the mechanical boundary conditions in this example are to apply a preload of (0, 500, 3000 N) at a distance of 11.5 mm from the end of the bolt at the section position (starting from 0 N, calculated every 500 N until 3000 N is calculated), select three completely separated non-collinear points (for three-dimensional models), fix the first point in three directions, restrict the second point in two directions of the vector normal from the first point to the second point, restrict the last point in the direction perpendicular to the plane formed by the three points, and specify the z-displacement of the bottom surface of the second layer of the connected part to be 0.

[0087] Step S6: Loading thermal boundary conditions.

[0088] Dissimilar metals with different thermal expansion coefficients will generate stress when the temperature changes, and the stress will affect the preload of the bolts. Especially in ultra-cold conditions, thermal stress may directly lead to bolt failure.

[0089] When the temperature is room temperature 293K, the first and second layers of the connected parts are stress-free. If we lower the temperature to 20K, we can find the stress caused by the mismatch of thermal expansion coefficients. Since we know the final temperature at each location, there is no need to solve the heat transfer problem. We can directly set the thermal boundary conditions to the transition from room temperature to the ultra-cold working temperature. This setting method can omit the setting of material heat capacity and thermal conductivity in terms of material thermophysical parameters, and only the thermal expansion coefficient is required for calculation.

[0090] Specifically, in this example, the thermal boundary condition is set to the transition from room temperature 293K to the ultra-cold working temperature of 20K.

[0091] Step S7: Define contact pairs.

[0092] Since the simplified modeling does not establish the actual finite element model of the thread, the stress caused by the mismatch of thermal expansion coefficients may cause penetration of the model, so it is necessary to further establish contact pairs.

[0093] Specifically, a contact pair is established between the lower surface of the gasket and the first layer of connected parts, and the augmented Lagrangian method is used to perform contact simulation calculations.

[0094] The meshes between the upper surface of the gasket and the lower surface of the bolt head, and between the thread engagement area and the surface of the underlying connection are treated with common nodes to transfer the stress caused by the mismatch of thermal expansion coefficients.

[0095] Step S8: Obtain the ultra-deep cooling bolt preload value through thermal-mechanical coupling simulation calculation and determine whether it meets the corresponding mechanical evaluation index.

[0096] According to the above settings, the ultra-deep cooling bolt preload value can be obtained by using thermal-mechanical coupling simulation calculation. Further, it can be determined by calculation whether the bolt preload and axial force under ultra-deep cooling conditions meet the mechanical evaluation indicators.

[0097] Specifically, the mechanical evaluation indicators include:

[0098] Breaking torque: KF pc d <T;

[0099] Bolt tangential force: F tc <[(0.3 / 1.1)×F pc ]-[(0.24 / 1.1)×F ac ]=(0.273×F pc )-(0.218×Fac );

[0100] Bolt axial force: compression bolt F ac <F pc ;

[0101] Tension bolt F ac <F a -F pc ;

[0102] Where: K is the tightening coefficient; F pc is the low temperature preload; d is the bolt diameter; T is the bolt breaking torque; F tc is the calculated low temperature tangential force; F pc F is the low temperature preload; ac is the calculated low-temperature axial force, which is positive when under tension and negative when under compression; F a is the allowable axial force;

[0103] When bolted connections are used, the acceptance criteria in the tangential direction are given by the slip resistance, the acceptance criteria in the axial direction are given by the preload when the bolt is in compression, and by the difference between the permissible axial force and the preload when the bolt is in tension;

[0104] The calculation formula of sliding resistance is:

[0105] F sa =(k s ×n×μ×F c ) / γ,

[0106] In the formula, k s is the geometric factor, k s =1.0; n is the number of friction interfaces; μ is the slip coefficient, μ=0.3 (C-grade surface); γ is the bolt safety factor 1.1;

[0107] F c =F pc -0.8×F ac ,

[0108] When the number of friction interfaces n is 1:

[0109] F sa =[(0.3 / 1.1)×F pc ]-[(0.24 / 1.1)×F ac ]=(0.273×F pc )-(0.218×F ac );

[0110] When the number of friction interfaces n is 2:

[0111] F sa =(0.546×F pc)-(0.436×F ac ).

[0112] Specifically, this example calculates the ultra-cold preload value corresponding to the preload force (0, 500, 3000N) applied at room temperature as follows: Figure 2 As shown in the table, when the bolt preload at room temperature reaches N, the bolt preload torque under ultra-cold conditions is less than the breaking torque, and the bolt axial force and tangential force meet the allowable conditions, such as Figure 3 shown.

[0113] The ultra-cold process involved in the present application generally refers to a working temperature below -180°C, about -200°C, and can be refrigerated by liquid nitrogen equipment.

[0114] Through the above-mentioned modeling equivalent method, it can be seen that the calculation amount of this scheme is between detailed modeling and simplified modeling, and the principles of equivalent model modeling and the minimum size of the grid that needs to be controlled are given; in addition, this scheme can use a simplified model with less calculation amount to perform thermal-mechanical coupling calculations without introducing internal stress, and ensure the convergence of the calculation; this scheme fills the gap in the verification method of the preload of dissimilar metal connection bolts under ultra-deep cold conditions, and gives an evaluation standard based on the destructive torque and the evaluation standard of the bolt tangential force and axial force, so as to judge the reliability of the bolt connection.

[0115] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0116] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for checking the preload force of ultra-deep cold dissimilar metal connection bolts based on simplified modeling, characterized in that: include: Defining bolt structural parameters, wherein defining bolt structural parameters includes defining a large washer thickness as hwasher; Define the structural parameters of dissimilar metal connected parts; Define the mechanical parameters and thermophysical parameters of bolts and connected parts; Simplify modeling and meshing; Mechanical boundary condition loading, thermal boundary condition loading; Define contact pairs; Obtain the preload value of ultra-deep cold bolts through thermal-mechanical coupling simulation and determine whether it meets the corresponding mechanical evaluation index; The definition of structural parameters of dissimilar metal connected parts includes: According to the thickness of the two connected parts in actual situations, the thickness of the first layer of connected parts is 1h1, and the thickness of the second layer of connected parts is 2h2; The minimum size of the simplified plate length, plate width and grid unit can be further determined based on the minimum size of the bolt and gasket structure. Define the simplified plate model with the length of the plate as length, the width of the plate as width, and the minimum size of the grid unit as gridmin. Then the following modeling conditions need to be met:

2. The method for checking the preload force of ultra-deep cold dissimilar metal connection bolts based on simplified modeling according to claim 1 is characterized in that: The bolt structure parameters are defined as follows: The defined bolt structural parameters include: bolt head fastener diameter e, bolt head thickness k, nominal diameter D, bolt length lbolt and thread length lthread, and the gasket structural parameters include: large gasket inner diameter d1, large gasket outer diameter d2 and the large gasket thickness hwasher.

3. The method for checking the preload force of ultra-deep cold dissimilar metal connection bolts based on simplified modeling according to claim 1 is characterized in that: The mechanical parameters and thermophysical parameters of the bolt and the connected parts materials are defined as follows: The mechanical parameters include density rho, Young's modulus E, and Poisson's ratio nu; the thermophysical parameters include thermal expansion coefficient alpha, and the deformation parameters calculated from the thermal expansion coefficient are related to the mechanical parameters.

4. The method for checking the preload force of ultra-deep cold dissimilar metal connection bolts based on simplified modeling according to claim 1 is characterized in that: The simplified modeling and meshing include: According to the defined bolt structural parameters, structural parameters of dissimilar metal connected parts, and mechanical parameters and thermophysical parameters of the bolt and connected parts materials, a simplified model for bolt preload analysis is established and the mesh is divided.

5. The method for checking the preload force of ultra-deep cold dissimilar metal connection bolts based on simplified modeling according to claim 1 is characterized in that: The mechanical boundary condition loading and thermal boundary condition loading include: Mechanical boundary conditions, including the preload of bolts at room temperature and the constraints of dissimilar metal connectors; The thermal boundary condition is the transition from room temperature to ultra-cold working temperature.

6. The method for checking the preload force of ultra-deep cold dissimilar metal connection bolts based on simplified modeling according to claim 5 is characterized in that: The mechanical boundary conditions, including the preload of the bolts at room temperature and the constraint conditions of the dissimilar metal connectors, include: A displacement constraint method with rigid body motion suppression is used: three completely separated non-collinear points are selected, the first point is fixed in three directions, the second point is restricted in two directions of the vector normal from the first point to the second point, and the last point is restricted in the direction perpendicular to the plane formed by the three points; Specify the z-displacement of the bottom surface of the second layer of the two connected parts to be 0.

7. The method for checking the preload force of ultra-deep cold dissimilar metal connection bolts based on simplified modeling according to claim 1 is characterized in that: The defined contact pair includes: A contact pair is established between the lower surface of the gasket and the first layer of the two connected parts, and the augmented Lagrangian method is used to perform contact simulation calculation to obtain the preload value of the ultra-deep cold bolt.

8. The method for checking the preload force of ultra-deep cold dissimilar metal connection bolts based on simplified modeling according to claim 1 is characterized in that: The method of obtaining the ultra-deep cold bolt preload value by thermal-mechanical coupling simulation calculation and judging whether the corresponding mechanical evaluation index is met includes: Mechanical evaluation indicators include: Breaking torque: KF pc d <T; Bolt tangential force: F tc <[(0.3 / 1.1)×F pc ]-[(0.24 / 1.1)×F ac ]=(0.273×F pc )-(0.218×F ac ); Bolt axial force: compression bolt F ac <F pc ; Tension bolt F ac <F a -F pc ; Where: K is the tightening coefficient; F pc is the low temperature preload; d is the bolt diameter; T is the bolt breaking torque; F tc is the calculated low temperature tangential force; F pc F is the low temperature preload; ac is the calculated low-temperature axial force, which is positive when under tension and negative when under compression; F a is the allowable axial force; When bolted connections are used, the acceptance criteria in the tangential direction are given by the slip resistance, the acceptance criteria in the axial direction are given by the preload when the bolt is in compression, and by the difference between the permissible axial force and the preload when the bolt is in tension; The calculation formula of sliding resistance is: F sa =(k s ×n×μ×F c ) / c, In the formula, k s is the geometric factor, k s =1.0; n is the number of friction interfaces; μ is the slip coefficient, μ=0.3 (C-grade surface); γ is the bolt safety factor 1.1; F c =F pc -0.8×F ac , When the number of friction interfaces n is 1: F sa =[(0.3 / 1.1)×F pc ]-[(0.24 / 1.1)×F ac ]=(0.273×F pc )-(0.218×F ac ); When the number of friction interfaces n is 2: F sa =(0.546×F pc )-(0.436×F ac )。

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