Finite Element Calculation Method and Strength Check Method for Mechanical State of Bolt Connection

Abstract

The present application provides a finite element calculation method and a strength verification method for the mechanical state of bolt connections, including: establishing a finite element model corresponding to the bolt connection structure according to the actual geometric structures of the components in the bolt connection structure; performing two finite element analysis steps, the first step including applying a fixed constraint to the bolt head in the finite element model and applying a rotation angle constraint to the nut in the finite element model; the second step including removing the fixed constraint applied to the bolt head in the finite element model, applying a fixed constraint to one of the clamped parts between the upper clamped part and the lower clamped part in the finite element model, and applying an external load to the other clamped part; and solving the clamped part flexibility, the load coefficient, and the second minimum pre-tightening force value according to the data obtained in the two finite element analysis steps. The technical solution shown in the present application can accurately verify the bolt connection strength and determine appropriate bolt specifications, material types, and tightening torques.

Description

Technical Field

[0001] This application relates to the technical field of mechanical design, and particularly to a finite element calculation method and a strength checking method for the mechanical state of bolt connections. Background Art

[0002] Bolt connection structures are widely used and applied to various mechanical products. During the product design stage, strength checking calculations need to be performed on bolt connections. The purpose of the calculations is to determine the appropriate bolt specifications, materials, and tightening torques on the premise of meeting the structural safety requirements (no fracture, no fatigue failure) and functional requirements (sealing performance, anti-loosening function). The so-called bolt specifications refer to the nominal diameters of bolts, which are standardized. Designers generally select from standard bolt specifications and rarely use non-standard specifications. The so-called tightening torque refers to the torque required for installing threaded connections, with the unit of Newton-meter.

[0003] Generally speaking, the strength checking calculation methods for bolt connections need to use many empirical formulas or empirical parameters, such as bolt flexibility, clamped part flexibility, and load coefficients. These empirical formulas or empirical parameters have large errors, resulting in inaccurate calculation results. Moreover, general bolt connection strength checking calculation methods cannot consider the stability of the overall stiffness of bolt connections and are not applicable to occasions with high requirements for the stiffness stability of bolt connections (that is, when the pre-tightening force fluctuates significantly, the stiffness of bolt connections remains basically unchanged or changes little). Summary of the Invention

[0004] The embodiments of this application provide a finite element calculation method and a strength checking method for the mechanical state of bolt connections, which can accurately check the strength of bolt connections and determine the appropriate bolt specifications, material types, and tightening torques.

[0005] In a first aspect, this application provides a finite element calculation method for the mechanical state of bolt connections, including:

[0006] According to the actual geometric structures of the components in the bolt connection structure, establish a finite element model corresponding to the bolt connection structure; wherein, the bolt connection structure includes bolts, nuts, upper clamped parts, and lower clamped parts; the finite element model includes: three-dimensional solid elements of each component, the actual material properties of each component, and the thread structures of bolts and nuts;

[0007] Set the boundary conditions of the finite element model. The boundary conditions include: thread contact interfaces, nut and upper clamped part contact interfaces, upper and lower clamped part contact interfaces, lower clamped part and bolt head contact interfaces; each contact interface is set with a corresponding friction coefficient;

[0008] Perform two finite element analysis steps. Among them, the first step includes applying a fixed constraint to the bolt head in the finite element model and applying a rotational angle constraint to the nut in the finite element model to simulate the tightening of the nut; the second step includes removing the fixed constraint applied to the bolt head in the finite element model, applying a fixed constraint to one of the clamped parts between the upper clamped part and the lower clamped part in the finite element model, and applying an external load F to the other clamped part A ;

[0009] Solve for the clamped part flexibility δ based on the data obtained in the two finite element analysis steps P , the load coefficient φ, and the second minimum pre-tightening force value F required to ensure the connection stiffness stability of the bolted connection structure Mmin2 .

[0010] In one implementation, solve for the clamped part flexibility δ based on the data obtained in the two finite element analysis steps P , including:

[0011] Extract the first pre-tightening force F of the bolt and the compression amount x of the inner hole length of the clamped part at the end of the first step; use Equation 1 to solve for the clamped part flexibility δ based on the compression amount x and the first pre-tightening force F K1 ; Equation 1 is: K1 Solve for the clamped part flexibility δ P ; Equation 1 is:

[0012]

[0013] In one implementation, solve for the load coefficient φ based on the data obtained in the two finite element analysis steps, including:

[0014] Extract the second pre-tightening force F of the bolt at the end of the second step K2 ;

[0015] Use Equation 2 to solve for the increase in pre-tightening force F A caused by the action of the external load F SA ; Equation 2 is:

[0016] F SA = F K2 - F K1 ;

[0017] Use Equation 3 to solve for the load coefficient φ; Equation 3 is:

[0018]

[0019] In one implementation, solve for the second minimum pre-tightening force value F Mmin2 , including:

[0020] Under multiple pre-tightening forces of different magnitudes, perform finite element analysis on the finite element model respectively to obtain the average displacement of the external load application nodes under each pre-tightening force;

[0021] Calculate the external load F respectively A and the ratio of the average displacement of the external load application nodes under each pre-tightening force to obtain the connection stiffness corresponding to each pre-tightening force, and plot the relationship curve between the connection stiffness and the pre-tightening force;

[0022] When the absolute value of the slope of the relationship curve is equal to or less than the preset critical value, determine the corresponding pre-tightening force as the second minimum pre-tightening force value F Mmin2 .

[0023] In a second aspect, the present application provides a method for checking the strength of bolt connections, including:

[0024] Step S1: Initially determine the nominal diameter and material type of the bolt;

[0025] Step S2: Input the tightening coefficient α of the bolt connection structure A , and the tightening coefficient α A is the ratio of the maximum value to the minimum value within the fluctuation range of the pre-tightening force obtained by applying the same torque to the bolt connection structure;

[0026] Step S3: Determine the minimum clamping force F required to ensure that there is no slip between the clamped parts under the working load KQ ; determine the interface pressure F required to ensure the sealing performance between the clamped parts KP ; determine the force F required to prevent the separation of the interface between the clamped parts KA ; determine the minimum clamping load F according to the minimum clamping force F KQ , the interface pressure F KP and the force F KA ; Kerf ;

[0027] Step S4: Determine the load coefficient φ according to the external load F A and the pre-tightening force increment F obtained based on the finite element calculation method KA ;

[0028] Step S5: Determine the pre-tightening force loss F caused by the surface embedding of the clamped interface due to the bolt flexibility δ S obtained according to the specifications and material-related parameters of the bolt and the clamped part flexibility δ P obtained based on the finite element calculation method; determine the pre-tightening force change ΔF caused by temperature change Z ; Vth ;

[0029] Step S6: According to the minimum clamping load F Kerf, load factor φ, maximum axial working load F Amax , preload loss F Z and preload change ΔF Vth , determine the first minimum preload F Mmin1 required considering preload loss and working load; obtain the second minimum preload F Mmin2 required to ensure the connection stiffness stability of the bolted connection structure based on the finite element calculation method; according to the first minimum preload F Mmin1 and the second minimum preload F Mmin2 , determine the minimum assembly preload F Mmin ;

[0030] Step S7: According to the tightening coefficient α A and the minimum assembly preload F Mmin , determine the maximum assembly preload F M max ;

[0031] Step S8: According to the specifications and material-related parameters of the bolt, determine the maximum allowable assembly preload F Mzul ; where, when the maximum assembly preload F M max and the maximum allowable assembly preload F Mzul do not meet the preset size relationship requirements, adjust the specifications and / or material types of the bolts, and re-execute steps S1 - S8 until the maximum assembly preload F M max and the maximum allowable assembly preload F Mzul meet the preset size relationship requirements;

[0032] Step S9: According to the maximum allowable assembly preload F Mzul , load factor φ, maximum axial working load F Amax , preload change ΔF Vth , specifications and material-related parameters of the bolt, determine the working stress σ red,B ; according to the bolt yield strength R P0.2min and the working stress σ red,B , determine the first safety factor S F ; where, when the first safety factor S F does not meet the preset requirements, adjust the specifications and / or material types of the bolts, and re-execute steps S1 - S9 until the first safety factor S F meets the preset requirements;

[0033] Step S10: According to the maximum axial additional load F SAmax borne by the bolt, the minimum axial additional load F SAmin borne by the bolt, the stress cross-sectional area A S of the bolt, determine the alternating stress σ a ; according to the alternating stress σa and the fatigue limit σ of the bolt under a preset number of fatigue cycles ASV , determine the second safety factor S D ; wherein, when the second safety factor S D does not meet the preset requirements, adjust the specification and / or material type of the bolt, and re-execute steps S1 - S10 until the second safety factor S D meets the preset requirements;

[0034] Step S11: According to the maximum allowable assembly pre-tightening force F Mzul and the minimum contact area A between the bolt head or nut end face and the clamped part pmin , determine the contact pressure p during bolt assembly M ; According to the maximum allowable assembly pre-tightening force F Mzul , the pre-tightening force loss F Z , the load factor φ, the maximum axial working load F Amax , the pre-tightening force change ΔF Vth and the minimum contact area A pmin , determine the contact pressure p during bolt operation B ; wherein, the contact pressure p M and the contact pressure p B are not simultaneously less than the allowable contact pressure p of the bolt G , adjust the specification and / or material type of the bolt, and re-execute steps S1 - S11 until the contact pressure p M and the contact pressure p B are simultaneously less than the allowable contact pressure p of the bolt G ;

[0035] Step S12: Determine the ultimate force F that causes the bolt to fracture and fail mS ; Determine the ultimate force F that causes the nut thread to loosen mGM ; Determine the ultimate force F that causes the bolt thread to loosen mGS ; Judge whether the ultimate force F that causes the bolt to fracture and fail mS is less than or equal to the minimum value of the ultimate force F that causes the nut thread to loosen mGM and the ultimate force F that causes the bolt thread to loosen mGS ; If the ultimate force F that causes the bolt to fracture and fail mS is greater than the minimum value of the ultimate force F that causes the nut thread to loosen mGM and the ultimate force F that causes the bolt thread to loosen mGS or the ultimate force F that causes the bolt to fracture and fail mS , the ultimate force F that causes the nut thread to loosen mGM , the ultimate force F that causes the bolt thread to loosen mGSIf at least one of them cannot be determined, select a nut with the same strength grade and specification as the bolt, skip step 12, and execute step 13;

[0036] Step S13: According to the maximum allowable assembly preload F Mzul , tightening coefficient α A , load coefficient φ, maximum axial working load F Amax , preload loss F Z and preload change ΔF Vth , determine the minimum remaining clamping load F A of the clamped part joint surface under the external load F KRmin ; Determine the lateral force F KQerf transmitted by friction at the clamped part joint surface; According to the minimum remaining clamping load F KRmin and lateral force F KQerf , determine the anti-slip safety factor S G ; According to the cross-sectional area A τ of the shear plane, the shear limit τ B of the bolt, and the maximum lateral working load F Qmax of the bolt connection structure, determine the shear stress safety factor S A ; Among them, if the anti-slip safety factor S G and the shear stress safety factor S A are not both greater than their respective thresholds, adjust the bolt specification and / or material type, and re-execute steps S1 - S13 until the anti-slip safety factor S G and the shear stress safety factor S A are both greater than their respective thresholds;

[0037] Step S14, according to the maximum allowable assembly preload F Mzul , determine the tightening torque M A ;

[0038] Step S15, output the finally determined bolt specification, material type and tightening torque M A .

[0039] In one implementation, step 3 specifically includes:

[0040] Use formula 4 to determine the minimum clamping force F KQ ; Formula 4 is:

[0041]

[0042] Among them, F Qmax is the maximum lateral working load of the bolt connection structure; q F is the number of connection interfaces for transmitting the lateral working load; μ Tminis the minimum friction coefficient of the connection interface; M Ymax is the maximum torque about the bolt axis; q M is the number of connection interfaces for torque transmission; r a is the equivalent friction radius of the clamped part interface;

[0043] Use Equation 5 to determine the interface pressure F KP ; Equation 5 is:

[0044]

[0045] where p i max is the contact pressure required for the bolt connection structure to ensure sealing; A D is the sealing area;

[0046] Use Equation 6 to determine the force F KA ; Equation 6 is:

[0047]

[0048] where F Amax is the maximum axial working load; a is the distance between the position where the external load is applied and the midline of the clamped part, M Bmax is the maximum bending moment acting on the bolt, u is the distance between the edge of the clamped part and the midline of the clamped part, s sym is the distance between the bolt axis and the midline of the clamped part, I BT is the moment of inertia of the clamped part at the connection interface;

[0049] Use Equation 7 to determine the minimum clamping load F Kerf ; Equation 7 is:

[0050] F Kerf = max(F KQ ; F KA + F KP );

[0051] Step S4 specifically includes:

[0052] According to the external load F A and the preload increase amount F KA obtained by the finite element calculation method based on the first aspect and its implementation manner above, determine the load coefficient φ;

[0053] Step S5 specifically includes:

[0054] According to the bolt flexibility δ S obtained from the parameters related to the bolt specifications and materials and the clamped part flexibility δ P, determine the preload loss F caused by the surface embedding of the clamped part's clamping interface Z ; determine the change in preload ΔF caused by temperature change Vth ; use Equation 8 to determine the bolt flexibility δ S , the

[0055] Equation 8 is:

[0056]

[0057] where, l1 is the length of the bolt shank, l GEW is the length of the unmeshed thread section, E S is the elastic modulus of the bolt material, A1 is the cross-sectional area of the shank, d is the nominal diameter of the bolt, and d3 is the minor diameter of the bolt;

[0058] Use Equation 9 to determine the preload loss F Z , Equation 9 is:

[0059]

[0060] where, f Z is the surface embedding amount;

[0061] Use Equation 10 to determine the change in preload ΔF Vth , Equation 10 is:

[0062]

[0063] where, l K is the total clamping length of the clamped part, α S is the linear expansion coefficient of the bolt material, α P is the linear expansion coefficient of the clamped part material, ΔT S is the temperature change of the bolt, ΔT P is the temperature change of the clamped part, E SRT is the elastic modulus of the bolt material at room temperature, E PRT is the elastic modulus of the clamped part material at room temperature, E ST is the elastic modulus of the bolt material after temperature change, E PT is the elastic modulus of the clamped part material after temperature change;

[0064] Step S6 specifically includes:

[0065] According to the minimum clamping load F Kerf , the load coefficient φ, the maximum axial working load F Amax , the preload loss F Z and the change in preload ΔF Vth , determine the first minimum preload F required considering preload loss and working loadMmin1 ; Obtain the second minimum pre-tightening force \(F\) required to ensure the connection stiffness stability of the bolt connection structure based on the finite element calculation method of the above first aspect and its implementation manner Mmin2 ; According to the first minimum pre-tightening force \(F\) Mmin1 and the second minimum pre-tightening force \(F\) Mmin2 , determine the minimum assembly pre-tightening force \(F\) Mmin ;

[0066] Use formula 11 to determine the first minimum pre-tightening force \(F\) Mmin1 , formula 11 is:

[0067] \(F\) Mmin1 = \(F\) Kerf +(1 - \(\varphi\))\(F\) Amax +\(F\) Z +\(\Delta F\) Vth ;

[0068] Use formula 12 to determine the minimum assembly pre-tightening force \(F\) Mmin ; Formula 12 is:

[0069] \(F\) Mmin = max(\(F\) Mmin1 ;\(F\) Mmin2 );

[0070] Step S7 specifically includes:

[0071] Use formula 13 to determine the maximum assembly pre-tightening force \(F\) M max ; Formula 13 is:

[0072] \(F\) M max = \(\alpha\) A ·\(F\) Mmin ;

[0073] Step S8 specifically includes:

[0074] Use formula 14 to determine the maximum allowable assembly pre-tightening force \(F\) Mzul ; Formula 14 is:

[0075]

[0076] where \(A_0\) is the minimum cross-sectional area of the bolt, \(\nu\) is the bolt utilization factor, \(R\) P0.2min is the yield strength of the bolt, \(d\) s is the equivalent diameter of the bolt stress section, \(d_2\) is the pitch diameter of the bolt, \(P\) is the pitch, \(\mu\) Gmin is the minimum friction coefficient of the thread.

[0077] In one implementation manner, step S9 specifically includes:

[0078] Use formula 15, formula 16 and formula 17 to determine the working stress \(\sigma\)red,B ;

[0079] Equation 15 is:

[0080]

[0081] Equation 16 is:

[0082]

[0083] Equation 17 is:

[0084]

[0085] where k τ is the shear stress reduction coefficient;

[0086] Determine the first safety factor S using Equation 18 F ; Equation 18 is:

[0087] S F = R P0.2min / σ red,B ;

[0088] Step S10 specifically includes:

[0089] Determine the alternating stress σ using Equation 19 a ; Equation 19 is:

[0090]

[0091] Determine the second safety factor S using Equation 20 D ; Equation 20 is:

[0092] S D = σ ASV / σ a ;

[0093] Step S11 specifically includes:

[0094] Determine the contact pressure p during assembly using Equation 21 M ; Equation 21 is:

[0095] p M = F Mzul / A pmin ;

[0096] Determine the contact pressure p when the bolt is working using Equation 22 B ; Equation 22 is:

[0097] p B = (F Mzul - F Z + φ · F A max-ΔF Vth ) / A pmin ;

[0098] Step S12 specifically includes:

[0099] Use formula 23 to determine the ultimate force F that causes the bolt to fail by fracture mS Is it less than or equal to the minimum value of the ultimate force F mGM and the ultimate force F mGS The formula 23 is:

[0100] F mS ≤min(F mGM , F mGS );

[0101] Step S13 specifically includes:

[0102] Use formula 24 to determine the minimum remaining clamping load F KRmin The formula 24 is:

[0103]

[0104] Use formula 25 to determine the lateral force F KQerf The formula 25 is:

[0105]

[0106] Use formula 26 to determine the anti-slip safety factor S G The formula 26 is:

[0107] S G = F KRmin / F KQerf

[0108] Use formula 27 to determine the shear stress safety factor S A The formula 27 is:

[0109]

[0110] Step S14 specifically includes:

[0111] Use formula 28 to determine the tightening torque M A The formula 28 is:

[0112]

[0113] where D Km is the equivalent diameter of the area on the bearing surface of the bolt head or nut that bears the frictional torque, and μ Kmin is the friction coefficient of the bearing surface area of the bolt head.

[0114] In one implementation, the maximum assembly pre-tightening force F M max and the maximum allowable assembly pre-tightening force F Mzul The preset size relationship requires that the maximum assembly pre-tightening force F M max be less than the maximum allowable assembly pre-tightening force F Mzul ;

[0115] The preset requirement for the first safety factor S F is that S F is greater than 1;

[0116] The preset number of fatigue cycles is 2×10 6 ;

[0117] The preset requirement for the second safety factor S D is that S D is greater than 1.2;

[0118] The threshold value of the anti-slip safety factor S G is 1.2;

[0119] The threshold value of the shear stress safety factor S A is 1.1;

[0120] The shear stress reduction coefficient k τ is 0.5.

[0121] Thirdly, the present application provides a finite element calculation device for the mechanical state of bolt connection. The finite element calculation device for the mechanical state of bolt connection includes a memory and one or more processors; the memory and the processor are coupled; the memory is used to store computer program code, and the computer program code includes computer instructions. When the processor executes the computer instructions, the bolt connection strength checking device executes the method in the first aspect and its implementation manners as described above.

[0122] Fourthly, the present application provides a bolt connection strength checking device. The bolt connection strength checking device includes a memory and one or more processors; the memory and the processor are coupled; the memory is used to store computer program code, and the computer program code includes computer instructions. When the processor executes the computer instructions, the bolt connection strength checking device executes the method in the second aspect and its implementation manners as described above.

[0123] The technical solution shown in the present application can accurately check the bolt connection strength and determine the appropriate bolt specifications, material types, and tightening torques. BRIEF DESCRIPTION OF THE DRAWINGS

[0124] To more clearly illustrate the technical solutions of the embodiments of the present application, the accompanying drawings required for the embodiments will be briefly introduced below. Obviously, for those of ordinary skill in the art, without creative efforts, other accompanying drawings can also be obtained based on these drawings.

[0125] Figure 1 is a flowchart of a finite element calculation method for the mechanical state of bolt connection provided by the embodiments of the present application;

[0126] Figure 2 is a schematic diagram of a bolt connection structure provided by the embodiments of the present application;

[0127] Figure 3 is a schematic diagram of a finite element model corresponding to the bolt connection structure provided by the embodiments of the present application;

[0128] Figure 4 is a schematic diagram of the relationship curve between connection stiffness and pre-tightening force provided by the embodiments of the present application. Specific Embodiments

[0129] The technical solutions of the embodiments of the present application will be clearly described below in conjunction with the accompanying drawings in the embodiments of the present application.

[0130] In the description of the present application, unless otherwise specified, " / " means "or". For example, A / B can represent A or B. The "and / or" herein is only a description of the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, "at least one" means one or more, and "a plurality" means two or more. The terms "first", "second", etc. do not limit the quantity and execution order, and the terms "first", "second", etc. do not necessarily limit to be different.

[0131] It should be noted that in the present application, words such as "exemplary" or "for example" are used to represent examples, illustrations or explanations. Any embodiment or design solution described as "exemplary" or "for example" in the present application should not be construed as being more preferred or having more advantages than other embodiments or design solutions. Exactly speaking, using words such as "exemplary" or "for example" aims to present related concepts in a specific manner.

[0132] The terms used in the embodiments part of the present application are only used to explain the specific embodiments of the present application, rather than aiming to limit the present application. The embodiments of the present application will be described in detail below in conjunction with the accompanying drawings.

[0133] The bolt connection structure is widely used in the mechanical field. During the product design process of the bolt connection structure, it is necessary to perform strength verification calculations on the bolt connection structure to meet the safety requirements and functional requirements of the bolt connection structure, that is, to ensure that the bolt connection structure cannot break, cannot suffer fatigue failure, and has good sealing performance and anti-loosening performance. Based on this, the bolt connection structure needs to determine the appropriate bolt specifications, materials, and tightening torques according to the results of the strength verification.

[0134] Traditional bolt connection strength verification methods usually perform strength verification on the bolt connection strength based on empirical formulas and empirical parameters. These empirical formulas and empirical parameters have large errors, resulting in inaccurate strength verification. At the same time, the existing bolt connection strength verification methods cannot verify the overall connection stiffness of the bolt connection structure and are not applicable in some scenarios with high requirements for the stability of bolt connection stiffness.

[0135] To solve the above problems, the embodiments of the present application provide a finite element calculation method and a strength verification method for the mechanical state of bolt connections.

[0136] Figure 1 It is a flowchart of a finite element calculation method for the mechanical state of bolt connections.

[0137] Figure 2 It is a schematic diagram of a bolt connection structure.

[0138] Figure 3 It is a schematic diagram of a finite element model corresponding to a bolt connection structure.

[0139] As Figure 1 、 Figure 2 and Figure 3 shown, the finite element calculation method for the mechanical state of bolt connections shown in the present application may include step S101-step S104.

[0140] It should be noted here that the finite element calculation method and strength verification method for the mechanical state of bolt connections provided by the embodiments of the present application can be applied to a single bolt connection structure or multiple bolt connection structures that can be disassembled, and calculations are performed for each single bolt connection structure after disassembly.

[0141] Step S101, establish a finite element model corresponding to the bolt connection structure according to the true geometric structures of the components in the bolt connection structure.

[0142] Among them, as Figure 2 shown, the bolt connection structure includes bolt 1, nut 2, upper clamped part 3, and lower clamped part 4; as Figure 3 shown, the finite element model includes: three-dimensional solid elements of each component, the true material properties of each component, and the thread structures of the bolt and nut.

[0143] The three-dimensional entity units of the components include: a three-dimensional entity unit 100 of the bolt 1 , a three-dimensional entity unit 200 of the nut 2 , a three-dimensional entity unit 300 of the upper clamped part 3 , and a three-dimensional entity unit 400 of the lower clamped part 4 .

[0144] Step S102, setting boundary conditions of the finite element model, the boundary conditions include: thread contact interface, nut and upper clamped part contact interface, upper and lower clamped part contact interface, lower clamped part and bolt head contact interface; each contact interface is set with a corresponding friction coefficient.

[0145] Step S103, performing two finite element analysis steps, wherein the first step includes applying a fixed constraint to the bolt head in the finite element model and applying an angle constraint to the nut in the finite element model to simulate the tightening of the nut; the second step includes removing the fixed constraint applied to the bolt head in the finite element model, applying a fixed constraint to one clamped part between the upper clamped part and the lower clamped part in the finite element model, and applying an external load F to the other clamped part. A .

[0146] Step S104, according to the data obtained in the two finite element analysis steps, solve the flexibility δ of the clamped part P , load factor φ and the second minimum preload value F required to ensure the connection stiffness stability of the bolt connection structure Mmin2 In some embodiments, the flexibility δ of the clamped component is solved based on the data obtained in the two finite element analysis steps. P ,include:

[0147] Extract the first preload F of the bolt at the end of the first step K1 And the compression amount x of the inner hole length of the clamped part. The clamped parts in this embodiment are collectively referred to as the upper clamped parts and the lower clamped parts. Among them, the compression amount of the inner hole length refers to the reduction in the length of the inner hole of the clamped part (i.e., the depth of the inner hole, which is also equal to the thickness of the clamped part at the hole position) compared with the initial state under the action of the preload force.

[0148] In some embodiments, using Formula 1, according to the compression amount x and the first preload force F K1 Solve the flexibility δ of the clamped part P ; Formula 1 is:

[0149]

[0150] In some embodiments, solving the load factor φ based on the data obtained in the two finite element analysis steps includes:

[0151] Extract the second preload F of the bolt at the end of the second step. K2 .

[0152] Using formula 2, solve for the increase in preload force F A caused by the action of the external load F SA ; Formula 2 is:

[0153] F SA = F K2 - F K1 .

[0154] Using formula 3, solve for the load coefficient φ; Formula 3 is:

[0155]

[0156] In some embodiments, according to the data obtained in two finite element analysis steps, solve for the second minimum preload force value F Mmin2 , including:

[0157] Under multiple preload forces of different magnitudes, perform finite element analysis on the finite element model respectively to obtain the average displacement of the external load application nodes under each preload force. Among them, the average displacement of the external load application nodes under each preload force is extracted from the finite element model.

[0158] Calculate the ratio of the external load F A to the average displacement of the external load application nodes under each preload force respectively to obtain the connection stiffness corresponding to each preload force, and plot the relationship curve between the connection stiffness and the preload force.

[0159] Figure 4 is a schematic diagram of the relationship curve between the connection stiffness and the preload force.

[0160] As Figure 4 shown, it should be noted here that as the preload force increases, the change trend of the connection stiffness is usually to increase rapidly first, then increase slowly, and finally tend to be stable. Based on this, it is necessary to perform finite element simulation analysis on preload forces of different magnitudes to obtain the magnitude of the connection stiffness corresponding to each preload force.

[0161] When the absolute value of the slope of the relationship curve is equal to or less than the preset critical value, determine the corresponding preload force as the second minimum preload force value F Mmin2 .

[0162] The embodiment of the present application also provides a method for checking the strength of bolt connections, and this method for checking the strength of bolt connections includes the following steps S1 - step S15.

[0163] Step S1: Initially determine the nominal diameter and material type of the bolt.

[0164] In specific implementation, the nominal diameter and material type of the bolt can be preliminarily determined according to experience. For example, the nominal diameter of the selected bolt is 10 cm, and the material is low-carbon alloy steel. Based on the nominal diameter and material type of the bolt, the connection strength of the bolt connection structure corresponding to the bolt can be checked.

[0165] Further, as Figure 2 shown, the bolt connection structure is subjected to a pre-tightening force at the nut and an interface clamping force at the interface between the upper clamped part and the lower clamped part. In the embodiments of the present application, the bolt connection strength is analyzed based on this bolt connection structure to determine the bolt connection strength possessed by the bolt.

[0166] It should be noted here that based on the nominal diameter and material type of the bolt, multiple mechanical parameters closely related to the material type, such as the strength grade, elastic modulus, yield strength, linear expansion coefficient, and fatigue limit of the material, can also be determined.

[0167] Step S2: Input the tightening coefficient α of the bolt connection structure A , the tightening coefficient α A is the ratio of the maximum value to the minimum value within the fluctuation range of the pre-tightening force obtained by applying the same torque to the bolt connection structure. It should be noted here that due to different friction coefficients and tightening processes, the pre-tightening force obtained by applying the same torque to the bolt has a fluctuation range, and the ratio of the maximum value to the minimum value within this fluctuation range is the tightening coefficient α A .

[0168] Step S3: Determine the minimum clamping force F required to ensure that the clamped parts do not slip under the working load KQ ; determine the interface pressure F required to ensure the sealing performance between the clamped parts KP ; determine the force F required to prevent the separation of the interface between the clamped parts KA ; determine the minimum clamping load F according to the minimum clamping force F KQ , the interface pressure F KP and the force F KA Kerf .

[0169] It should be noted here that the minimum clamping force F KQ required to ensure that the clamped parts do not slip under the working load can largely ensure the anti-loosening performance of the bolt connection structure and can also prevent the bolt from being sheared and broken.

[0170] In some embodiments, the minimum clamping force F KQ is determined using Equation 4; Equation 4 is:

[0171]

[0172] Where FQmax is the maximum transverse working load of the bolt connection structure; q F is the number of connection interfaces for transmitting the transverse working load; μ Tmin is the minimum friction coefficient of the connection interface; M Ymax is the maximum torque about the bolt axis; q M is the number of connection interfaces for transmitting torque; r a is the equivalent friction radius of the clamped part interface.

[0173] In some embodiments, the interface pressure F is determined using Equation 5 KP ; Equation 5 is:

[0174] F KP = A D · p imax .

[0175] Wherein, p i max is the contact pressure required to ensure the sealing performance of the bolt connection structure; A D is the sealing area.

[0176] In some embodiments, the force F is determined KA ; Equation 6 is:

[0177]

[0178] Wherein, F Amax is the maximum axial working load; a is the distance between the position where the external load is applied and the midline of the clamped part, M Bmax is the maximum bending moment acting on the bolt, u is the distance between the edge of the clamped part and the midline of the clamped part, s sym is the distance between the bolt axis and the midline of the clamped part, I BT is the moment of inertia of the clamped part at the connection interface.

[0179] In some embodiments, the minimum clamping load F is determined using Equation 7 Kerf ; Equation 7 is:

[0180] F Kerf = max(F KQ ; F KA + F KP ).

[0181] Step S4: Determine the load coefficient φ according to the external load F A and the pre-tightening force increment F KA obtained based on the finite element calculation method in the above embodiments.

[0182] Specifically, the load coefficient φ is determined according to Equation 3 above.

[0183] Step S5: Determine the bolt flexibility δ based on the specifications of the bolt and parameters related to its material S and the flexibility δ of the clamped component obtained based on the finite element calculation method in the above embodiments P , and determine the preload loss F caused by surface embedding at the clamped interface of the clamped component Z ; determine the preload change ΔF caused by temperature variation Vth .

[0184] In some embodiments, use Equation 8 to determine the bolt flexibility δ S , and Equation 8 is:

[0185]

[0186] wherein, l1 is the length of the bolt shank, l GEW is the length of the unmeshed thread section, E S is the elastic modulus of the bolt material, A1 is the cross-sectional area of the shank, d is the nominal diameter of the bolt, and d3 is the minor diameter of the bolt.

[0187] In some embodiments, use Equation 9 to determine the preload loss F Z , and Equation 9 is:

[0188]

[0189] wherein, f Z is the surface embedding amount.

[0190] In some embodiments, use Equation 10 to determine the preload change ΔF Vth , and Equation 10 is:

[0191]

[0192] wherein, l K is the total clamping length of the clamped component, α S is the linear expansion coefficient of the bolt material, α P is the linear expansion coefficient of the clamped component material, ΔT S is the temperature change of the bolt, ΔT P is the temperature change of the clamped component, E SRT is the elastic modulus of the bolt material at room temperature, E PRT is the elastic modulus of the clamped component material at room temperature, E ST is the elastic modulus of the bolt material after temperature change, E PT is the elastic modulus of the clamped component material after temperature change.

[0193] Step S6: According to the minimum clamping load F Kerf , load factor φ, and maximum axial working load F Amax, preload loss F Z and preload variation ΔF Vth , determine the first minimum preload F Mmin1 required considering preload loss and working load; obtain the second minimum preload F Mmin2 required to ensure the connection stiffness stability of the bolt connection structure based on the finite element calculation method in the above embodiments; according to the first minimum preload F Mmin1 and the second minimum preload F Mmin2 , determine the minimum assembly preload F Mmin ; in some embodiments, use formula 11 to determine the first minimum preload F Mmin1 , and formula 11 is:

[0194] F Mmin1 = F Kerf +(1 - φ)F Amax + F Z +ΔF Vth .

[0195] In some embodiments, use formula 12 to determine the minimum assembly preload F Mmin ; formula 12 is:

[0196] F Mmin = max(F Mmin1 ; F Mmin2 ).

[0197] Step S7: According to the tightening coefficient α A and the minimum assembly preload F Mmin , determine the maximum assembly preload F M max . In some embodiments, use formula 13 to determine the maximum assembly preload F M max ; formula 13 is:

[0198] F M max = α A ·F Mmin .

[0199] Step S8: According to the specifications and material-related parameters of the bolts, determine the maximum allowable assembly preload F Mzul of the bolts; wherein, when the maximum assembly preload F M max and the maximum allowable assembly preload F Mzul do not meet the preset size relationship requirements, adjust the specifications and / or material types of the bolts, and re-execute steps S1 - S8 until the maximum assembly preload F M max and the maximum allowable assembly preload F Mzul meet the preset size relationship requirements.

[0200] In some embodiments, the maximum assembly preload FM max and the maximum allowable assembly pre-tightening force F Mzul The preset size relationship requires that the maximum assembly pre-tightening force F M max is less than the maximum allowable assembly pre-tightening force F Mzul .

[0201] In some embodiments, the maximum allowable assembly pre-tightening force F is determined using Equation 14 Mzul ; Equation 14 is:

[0202]

[0203] where A0 is the minimum cross-sectional area of the bolt, v is the bolt utilization factor, R P0.2min is the yield strength of the bolt, d s is the equivalent diameter of the stress section of the bolt, d2 is the pitch diameter of the bolt, P is the pitch, and μ Gmin is the minimum friction coefficient of the thread.

[0204] Step S9: Determine the working stress σ according to the maximum allowable assembly pre-tightening force F Mzul , the load factor φ, the maximum axial working load F Amax , the pre-tightening force variation ΔF Vth , and the parameters related to the specification and material of the bolt; determine the first safety factor S according to the bolt yield strength R red,B ; and the working stress σ P0.2min ; where, when the first safety factor S red,B does not meet the preset requirements, adjust the specification and / or material type of the bolt, and re-execute steps S1 - S9 until the first safety factor S F meets the preset requirements. F F F In some embodiments, the preset requirement for the first safety factor S

[0205] is that S F is greater than 1. In this way, it can be ensured that the bolt material does not undergo plastic failure. F In some embodiments, the working stress σ is determined using Equation 15, Equation 16, and Equation 17

[0206] ; red,B ;

[0207] Equation 15 is:

[0208]

[0209] Equation 16 is:

[0210]

[0211] Equation 17 is:

[0212]

[0213] where k τ is the shear stress reduction coefficient.

[0214] In some embodiments, the shear stress reduction coefficient k τ is 0.5.

[0215] In some embodiments, the first safety factor S is determined using Equation 18 F ; Equation 18 is:

[0216] S F = R P0.2min / σ red,B .

[0217] Step S10: Determine the alternating stress σ based on the maximum axial additional load F SAmax borne by the bolt, the minimum axial additional load F SAmin borne by the bolt, and the stress cross-sectional area A S of the bolt; determine the second safety factor S based on the alternating stress σ a and the fatigue limit σ a of the bolt under a preset number of fatigue cycles; where when the second safety factor S ASV does not meet the preset requirements, adjust the specification and / or material type of the bolt, and re-execute Steps S1 - S10 until the second safety factor S D meets the preset requirements. D D 6

[0218] In some embodiments, the preset number of cycles is 2×10 6 6 .

[0219] In some embodiments, the preset requirement for the second safety factor S D is that S D is greater than 1.2. In this way, it can be ensured that the bolt will not undergo fatigue failure.

[0220] In some embodiments, the alternating stress σ is determined using Equation 19 a ; Equation 19 is:

[0221]

[0222] In some embodiments, the second safety factor S is determined using Equation 20 D ; Equation 20 is:

[0223] S D = σ ASV / σ a .

[0224] Step S11: According to the maximum allowable assembly pre-tightening force F Mzul and the minimum contact area A between the bolt head or nut end face and the clamped part pmin , determine the contact pressure p during bolt assembly M ; According to the maximum allowable assembly pre-tightening force F Mzul , pre-tightening force loss F Z , load factor φ, maximum axial working load F Amax , pre-tightening force change ΔF Vth and the minimum contact area A pmin , determine the contact pressure p during bolt operation B ; Among them, the contact pressure p M and the contact pressure p B are not simultaneously less than the allowable contact pressure p of the bolt G , adjust the bolt specification and / or material type, and re-execute steps S1 - S11 until the contact pressure p M and the contact pressure p B are simultaneously less than the allowable contact pressure p of the bolt G . In this way, it is possible to avoid the contact surface being crushed due to excessive pressure on the contact surface between the bolt and the clamped part.

[0225] In some embodiments, the contact pressure p during assembly is determined using Equation 21 M ; Equation 21 is:

[0226] p M = F Mzul / A pmin .

[0227] In some embodiments, the contact pressure p during bolt operation is determined using Equation 22 B ; Equation 22 is:

[0228] p B = (F Mzul - F Z + φ · F A max - ΔF Vth ) / A pmin .

[0229] Step S12: Determine the ultimate force F that causes the bolt to fracture and fail mS ; Determine the ultimate force F that causes the nut thread to loosen mGM ; Determine the ultimate force F that causes the bolt thread to loosen mGS ; Judge whether the ultimate force F that causes the bolt to fracture and fail mS is less than or equal to the ultimate force F that causes the nut thread to loosen mGM and the ultimate force F that causes the bolt thread to loosen mGSThe minimum value in; if the ultimate force F that causes the bolt to fracture and fail mS is greater than the ultimate force F that causes the nut thread to become loose mGM and the ultimate force F that causes the bolt thread to become loose mGS the minimum value in, or the ultimate force F that causes the bolt to fracture and fail mS , the ultimate force F that causes the nut thread to become loose mGM , the ultimate force F that causes the bolt thread to become loose mGS in at least one of them cannot be determined, select a nut with the same strength grade and specification as the bolt, skip and execute step 12, and execute step 13. In this way, it is possible to prevent thread disengagement failure in the bolt connection and make the bolt thread and the internal thread have sufficient screwing strength.

[0230] In some embodiments, use formula 23 to determine whether the ultimate force F that causes the bolt to fracture and fail mS is less than or equal to the minimum value of the ultimate force F mGM and the ultimate force F mGS in; formula 23 is:

[0231] F mS ≤min(F mGM ,F mGS ).

[0232] Step S13: According to the maximum allowable assembly preload F Mzul , the tightening coefficient α A , the load coefficient φ, the maximum axial working load F Amax , the preload loss F Z and the preload change ΔF Vth , determine the minimum remaining clamping load F A of the clamped part joint surface under the external load F KRmin ; determine the lateral force F KQerf transmitted by friction of the clamped part joint surface; according to the minimum remaining clamping load F KRmin and the lateral force F KQerf , determine the anti-slip safety factor S G ; according to the cross-sectional area A τ of the shear plane, the shear limit τ B of the bolt, and the maximum lateral working load F Qmax of the bolt connection structure, determine the shear stress safety factor S A ; where, if the anti-slip safety factor S G and the shear stress safety factor S A are not both greater than their respective thresholds, adjust the specification and / or material type of the bolt, and re-execute steps S1 - S13 until the anti-slip safety factor S G and the shear stress safety factor SA Both are greater than their respective thresholds.

[0233] In some embodiments, the minimum remaining clamping load F is determined using Equation 24 KRmin ; Equation 24 is:

[0234]

[0235] In some embodiments, the lateral force F is determined using Equation 25 KQerf ; Equation 25 is:

[0236]

[0237] In some embodiments, the anti-slip safety factor S is determined using Equation 26 G ; Equation 26 is:

[0238] S G = F KRmin / F KQerf .

[0239] In some embodiments, the threshold value of the anti-slip safety factor S G is 1.2. In this way, it can be ensured that the joint surface of the clamping component does not slip under the action of the external load.

[0240] In some embodiments, the shear stress safety factor S is determined using Equation 27 A ; Equation 27 is:

[0241]

[0242] In some embodiments, the threshold value of the shear stress safety factor S A is 1.1. In this way, shear failure of the bolt due to overload can be avoided.

[0243] Step S14, determine the tightening torque M according to the maximum allowable assembly pre-tightening force F Mzul . A .

[0244] In some embodiments, the tightening torque M is determined using Equation 28 A ; Equation 28 is:

[0245]

[0246] where D Km is the equivalent diameter of the area on the bearing surface of the bolt head or nut that bears the frictional torque, and μ Kmin is the friction coefficient of the bearing surface area of the bolt head.

[0247] Step S15, output the finally determined bolt specifications, material types, and tightening torque MA 。

[0248] The technical solution shown in this application can accurately calculate the empirical formulas and empirical parameters in the traditional bolt connection strength check method through the finite element calculation method, and can accurately calculate the stiffness of the bolt connection. On this basis, a complete bolt connection strength check calculation method is established, solving the problem of insufficient accuracy in calculating using empirical formulas and the problem of being unable to calculate the overall stiffness of the bolt connection structure, improving the accuracy of bolt connection strength check, being able to accurately check the connection strength of bolts, determine appropriate bolt specifications, material types, and tightening torques, and being applicable to occasions with high requirements for the stiffness stability of bolt connections.

[0249] In addition, the finite element calculation method and strength check method for the mechanical state of bolt connections shown in this application can also be programmed, thus facilitating the formation of an operating software system for convenient automated application and being beneficial to improving the bolt check efficiency.

[0250] This application also provides a finite element calculation device for the mechanical state of bolt connections. The finite element calculation device for the mechanical state of bolt connections includes a memory and one or more processors; the memory and the processor are coupled; the memory is used to store computer program code, and the computer program code includes computer instructions. When the processor executes the computer instructions, the bolt connection strength check device executes the method in any embodiment of the finite element calculation method for the mechanical state of bolt connections.

[0251] This application also provides a bolt connection strength check device. The bolt connection strength check device includes a memory and one or more processors; the memory and the processor are coupled; the memory is used to store computer program code, and the computer program code includes computer instructions. When the processor executes the computer instructions, the bolt connection strength check device executes the method in any embodiment of the bolt connection strength check method.

[0252] The above content is only the specific implementation manner of this application, but the protection scope of this application is not limited thereto. Any changes or substitutions within the technical scope disclosed in this application should be covered by the protection scope of this application. Therefore, the protection scope of this application should be subject to the protection scope of the claims.

Claims

1. A finite element calculation method for the mechanical state of bolt connection, characterized in that Comprising: Establish a finite element model corresponding to the bolt connection structure according to the true geometric structures of the components in the bolt connection structure; wherein, the bolt connection structure includes a bolt, a nut, an upper clamped part, and a lower clamped part; the finite element model includes: three-dimensional solid elements of each component, the true material properties of each component, and the thread structures of the bolt and the nut; Set the boundary conditions of the finite element model, where the boundary conditions include: the thread contact interface, the contact interface between the nut and the upper clamped part, the contact interface between the upper and lower clamped parts, and the contact interface between the lower clamped part and the bolt head; a corresponding friction coefficient is set for each contact interface; Execute two finite element analysis steps, where the first step includes applying a fixed constraint to the bolt head in the finite element model and applying a rotational angle constraint to the nut in the finite element model to simulate the tightening of the nut; the second step includes removing the fixed constraint applied to the bolt head in the finite element model, applying a fixed constraint to one of the clamped parts between the upper clamped part and the lower clamped part in the finite element model, and applying an external load to the other clamped part ; Solve for the flexibility of the clamped part based on the data obtained in the two finite element analysis steps , the load coefficient , and the second minimum pre-tightening force value required to ensure the connection stiffness stability of the bolt connection structure ; Among them, according to the data obtained in the two finite element analysis steps, solve the load coefficient , including: Extract the second pre-tightening force of the bolt at the end of the second step ; Using formula 2, solve for the increase in preload caused by the action of the external load ; The formula 2 is: ； Solve for the load factor using Equation 3 ; Equation 3 is as follows: 。 2. The finite element calculation method for the mechanical state of bolt connection according to claim 1, characterized in that, Solve for the flexibility of the clamped part according to the data obtained in the two finite element analysis steps , including: Extract the first pre-tightening force of the bolt at the end of the first step and the compression amount of the inner hole length of the clamped part ; Using formula 1, according to the compression amount and the first pre-tightening force to solve the flexibility of the clamped part ; The formula 1 is: 。 3. The finite element calculation method for the mechanical state of bolt connection according to claim 2, characterized in that, Solve the second minimum pre-tightening force value according to the data obtained in the two finite element analysis steps , including: Under multiple pre-tightening forces of different magnitudes, perform finite element analysis on the finite element model respectively to obtain the average displacement of the external load application nodes under each pre-tightening force; Calculate the external loads separately Calculate the ratio of the external load to the average displacement of the external load application nodes under each pre-tightening force, obtain the connection stiffness corresponding to each pre-tightening force, and plot the relationship curve between the connection stiffness and the pre-tightening force; When the absolute value of the slope of the relationship curve is equal to or less than a preset critical value, the corresponding pre-tightening force is determined as the second minimum pre-tightening force value .

4. A bolt connection strength checking method applied to the finite element calculation method of the mechanical state of the bolt connection as described in claim 3, characterized in that, Comprising: Step S1: Initially determine the nominal diameter and material type of the bolt; Step S2: Input the tightening coefficient of the bolt connection structure , the tightening coefficient is the ratio of the maximum value to the minimum value within the fluctuation range of the pre-tightening force obtained by applying the same torque to the bolt connection structure; Step S3: Determine the minimum clamping force required to ensure that there is no slippage between the workpieces under the working load ; Determine the interface pressure required to ensure the sealing performance between the clamped parts ; Determine the force required to prevent interfacial separation between the parts to be clamped ; Determine the minimum clamping force according to , interfacial pressure and force Determine the minimum clamping load ; Step S4: Determine the load coefficient according to the external load and the pre-tightening force increment obtained based on the finite element calculation method , ; Step S5: The bolt flexibility obtained based on the specifications and material-related parameters of the bolt and the flexibility of the clamped parts obtained based on the finite element calculation method , determine the amount of preload loss caused by the surface embedding of the clamped part clamping interface ; determine the amount of preload change caused by temperature changes ; Step S6: Based on the minimum clamping load , load factor , maximum axial working load , preload loss and preload change , determine the first minimum preload required considering preload loss and working load; The second minimum pre-tightening force required to ensure the connection stiffness stability of the bolt connection structure is obtained based on the finite element calculation method ; According to the first minimum pre-tightening force and the second minimum pre-tightening force , determine the minimum assembly pre-tightening force ; Step S7: Determine the maximum assembly pre-tightening force according to the tightening coefficient and the minimum assembly pre-tightening force ; Step S8: Determine the maximum allowable assembly pre-tightening force of the bolt according to the specifications of the bolt and the parameters related to the material ; where, when the maximum assembly pre-tightening force and the maximum allowable assembly pre-tightening force do not meet the requirements of the preset magnitude relationship, adjust the specifications and / or material types of the bolts, and re-execute steps S1 - S8 until the maximum assembly pre-tightening force and the maximum allowable assembly pre-tightening force meet the requirements of the preset magnitude relationship; Step S9: Based on the maximum allowable assembly pre-tightening force , the load factor , the maximum axial working load , the pre-tightening force variation , and the parameters related to the specifications and materials of the bolts, determine the working stress ; Based on the bolt yield strength and the working stress , determine the first safety factor ; Among them, when the first safety factor does not meet the preset requirements, adjust the specifications and / or material types of the bolts, and re-execute steps S1 - S9 until the first safety factor meets the preset requirements; Step S10: Determine the alternating stress based on the maximum axial additional load borne by the bolt , the minimum axial additional load borne by the bolt , and the stress cross-sectional area of the bolt ; Determine the second safety factor based on the alternating stress and the fatigue limit of the bolt under a preset number of fatigue cycles ; Among them, when the second safety factor does not meet the preset requirements, adjust the specifications and / or material types of the bolts, and re-execute steps S1 - S10 until the second safety factor meets the preset requirements; Step S11: According to the maximum allowable assembly pre-tightening force and the minimum contact area between the bolt head or nut end face and the clamped parts , determine the contact pressure during bolt assembly ; According to the maximum allowable assembly pre-tightening force , pre-tightening force loss , load coefficient , maximum axial working load , pre-tightening force variation and the minimum contact area , determine the contact pressure during bolt operation ; Among them, the contact pressure and the contact pressure shall not be less than the allowable contact pressure of the bolt at the same time. Adjust the bolt specifications and / or material types, and re-execute steps S1 - S11 until the contact pressure and the contact pressure are both less than the allowable contact pressure of the bolt ; Step S12: Determine the ultimate force that causes the bolt to fail by fracture ; Determine the ultimate force that causes the nut thread to become loose ; Determine the ultimate force that causes the bolt thread to become loose ; Judge whether the ultimate force that causes the bolt to fail by fracture is less than or equal to the minimum value of the ultimate force that causes the nut thread to become loose and the ultimate force that causes the bolt thread to become loose ; If the ultimate force that causes the bolt to fail by fracture is greater than the minimum value of the ultimate force that causes the nut thread to become loose and the ultimate force that causes the bolt thread to become loose or the ultimate force that causes the bolt to fail by fracture , the ultimate force that causes the nut thread to become loose , the ultimate force that causes the bolt thread to become loose cannot be determined at least one of them, select a nut with the same strength grade and specification as the bolt, skip and execute step 12, and execute step 13; Step S13: Based on the maximum allowable assembly pre-tightening force , tightening coefficient , load coefficient , maximum axial working load , pre-tightening force loss and pre-tightening force variation , determine the minimum remaining clamping load of the clamped part joint surface under the external load ; determine the lateral force transmitted by friction at the clamped part joint surface; based on the minimum remaining clamping load and the lateral force , determine the anti-slip safety factor ; based on the cross-sectional area of the shear plane, the shear limit of the bolt, and the maximum lateral working load of the bolt connection structure, determine the shear stress safety factor ; where, if the anti-slip safety factor and the shear stress safety factor do not both exceed their respective thresholds, adjust the bolt specifications and / or material types, and re-execute steps S1 - S13 until the anti-slip safety factor and the shear stress safety factor both exceed their respective thresholds; Step S14, determine the tightening torque according to the maximum allowable assembly pre-tightening force ; ; Step S15, output the finally determined bolt specification, material type, and tightening torque .

5. The bolt connection strength checking method according to claim 4, characterized in that, Said step S3 specifically includes: Determine the minimum clamping force using Equation 4 ; Equation 4 is as follows: ； Among them, is the maximum lateral working load of the bolt connection structure; is the number of connection interfaces for transmitting the lateral working load; is the minimum friction coefficient of the connection interface; is the maximum torque about the bolt axis; is the number of connection interfaces for transmitting torque; is the equivalent friction radius of the clamped part interface; Determine the interface pressure using Equation 5 ; Equation 5 is as follows: ； Among them, is the contact pressure required for the bolt connection structure to ensure tightness; is the sealing area; Determine the said force using Equation 6 ; Equation 6 is as follows: ； Among them, is the maximum axial working load; is the distance between the position where the external load is applied and the midline of the clamped part, is the maximum bending moment acting on the bolt, is the distance between the edge of the clamped part and the midline of the clamped part, is the distance between the axis of the bolt and the midline of the clamped part, is the moment of inertia of the clamped part at the connection interface; Determine the minimum clamping load using Equation 7 ; Equation 7 is as follows: ； Said step S4 specifically includes: According to the external load and the increase in preload obtained by the finite element calculation method according to claim 1 , determine the load coefficient ; Said step S5 specifically includes: The bolt flexibility obtained based on the specifications of the bolt and the parameters related to the material and the flexibility of the clamped parts obtained based on the finite element calculation method according to claim 1 , determine the amount of preload loss caused by surface embedding at the clamping interface of the clamped parts ; determine the amount of preload change caused by temperature change ; Determine the bolt flexibility using Equation 8 , where Equation 8 is as follows: ； Among them, is the length of the bolt shank, is the length of the unmeshed thread section, is the elastic modulus of the bolt material, is the cross-sectional area of the shank, is the nominal diameter of the bolt, is the minor diameter of the bolt; Determine the pre-tightening force loss using Equation 9 , and Equation 9 is as follows: ； Among them, is the surface embedding amount; Determine the pre-tightening force variation using Equation 10 , and Equation 10 is as follows: ； Among them, is the total clamping length of the clamped parts, is the linear expansion coefficient of the bolt material, is the linear expansion coefficient of the clamped part material, is the temperature change of the bolt, is the temperature change of the clamped part, is the elastic modulus of the bolt material at room temperature, is the elastic modulus of the clamped part material at room temperature, is the elastic modulus of the bolt material after temperature change, is the elastic modulus of the clamped part material after temperature change; Said step S6 specifically includes: According to the minimum clamping load , the load factor , the maximum axial working load , the preload loss and the preload variation , determine the first minimum preload required considering the preload loss and the working load ; obtain the second minimum preload required to ensure the connection stiffness stability of the bolted connection structure according to the finite element calculation method described in claim 1 ; according to the first minimum preload and the second minimum preload , determine the minimum assembly preload ; Determine the first minimum pre-tightening force using Equation 11 , where Equation 11 is as follows: ； Determine the minimum assembly pre-tightening force by using Equation 12 ; Equation 12 is as follows: ； Said step S7 specifically includes: Determine the maximum assembly pre-tightening force using Equation 13 ; Equation 13 is as follows: ； Said step S8 specifically includes: Determine the maximum allowable assembly pre-tightening force using Equation 14 ; Equation 14 is as follows: ； Among them, is the minimum cross-sectional area of the bolt, is the utilization factor of the bolt, is the yield strength of the bolt, is the equivalent diameter of the stress section of the bolt, is the pitch diameter of the bolt, is the pitch, is the minimum friction coefficient of the thread.

6. The bolt connection strength checking method according to claim 5, characterized in that, Said step S9 specifically includes: Determine the working stress using Equation 15, Equation 16, and Equation 17 ; Said formula 15 is: ； Said formula 16 is: ； Said formula 17 is: ； Among them, is the shear stress reduction coefficient; Determine the first safety factor using Equation 18 ; Equation 18 is as follows: ； Said step S10 specifically includes: Determine the alternating stress using Equation 19 ; Equation 19 is as follows: ； Determine the second safety factor using Formula 20 ; Formula 20 is as follows: ； Said step S11 specifically includes: Determine the contact pressure during the assembly using Equation 21 ; Equation 21 is as follows: ； Determine the contact pressure of the bolt during operation using Equation 22 ; Equation 22 is as follows: ； Said step S12 specifically includes: Use formula 23 to determine the ultimate force that causes the bolt to fracture and fail Whether it is less than or equal to the ultimate force and the minimum value of the ultimate force ; The formula 23 is as follows: ； Said step S13 specifically includes: Determine the minimum remaining clamping load using Equation 24 ; Equation 24 is as follows: ； Determine the lateral force using Equation 25 ; Equation 25 is as follows: ； Determine the anti-slip safety factor using Equation 26 ; Equation 26 is as follows: = ； Determine the shear stress safety factor using Equation 27 ; Equation 27 is as follows: ； Said step S14 specifically includes: Determine the tightening torque using Equation 28 ; Equation 28 is as follows: ； Among them, is the equivalent diameter of the area on the bearing surface of the bolt head or nut that bears the frictional moment, is the friction coefficient of the area on the bearing surface of the bolt head.

7. The bolt connection strength checking method according to claim 6, characterized in that, The maximum assembly pre-tightening force and the maximum allowable assembly pre-tightening force The preset size relationship requirement is that the maximum assembly pre-tightening force is less than the maximum allowable assembly pre-tightening force ; The first safety factor has a preset requirement of being greater than 1; The preset number of times of the fatigue cycle is 2×10 6 ; The second safety factor shall meet the preset requirement that is greater than 1.2; The anti-slip safety factor has a threshold value of 1.2; The shear stress safety factor has a threshold value of 1.1; The shear stress reduction factor is 0.

5.

8. A finite element calculation device for the mechanical state of bolt connection, characterized in that, The finite element calculation device for the mechanical state of the bolt connection executes the method according to any one of claims 1-3.

9. A bolt connection strength checking device, characterized in that, The bolt connection strength checking device executes the method according to any one of claims 4-7.

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