A method for determining the amount of axial force loss caused by the assembly clearance of a bolt connection structure

Abstract

The present invention relates to the technical field of bolt assembly, and in particular to a method for determining the amount of axial force loss caused by the assembly clearance of a bolt connection structure, which comprises the following steps: S1, establishing a finite element model for the bolt connection structure; S2, defining the relationships between the various parts in the bolt connection structure; S3, calculating the bolt pre-tightening axial force; S4, determining whether there is a non-linear material among the materials used for the various parts in the bolt connection structure, and if so, proceeding to the next step; S5, defining the non-linear material properties; S6, applying the bolt pre-tightening force to the bolt; S7, performing an analysis and calculation on the finite element model to obtain a relationship curve between the contact pressure of the contact surface of the connected parts and time in the bolt connection structure; S8, calculating the amount of axial force loss caused by the assembly clearance of the bolt connection structure according to the relationship curve. The present invention can improve the calculation accuracy and calculation speed, and has strong adaptability.

Description

Technical Field

[0001] The present invention relates to the technical field of bolt assembly, and particularly to a method for determining the amount of axial force loss caused by the assembly clearance of a bolt connection structure. Background Art

[0002] As one of the basic connection forms of automotive parts, the bolt connection structure is responsible for ensuring the rigid connection relationship between the connected parts.

[0003] During the operation of the vehicle, the bolt connection structure has to bear large and variable impact loads. In order to ensure the controllability and safety of the vehicle, the bolt connection structure should provide the minimum clamping force that meets various operating conditions to ensure that the connected parts do not undergo relative displacement, and at the same time, it should ensure that the connected parts do not undergo plastic deformation and damage under the action of the maximum pre-tightening force. However, due to the tolerances of the parts connected by the bolt connection structure, there will be a certain assembly clearance after the bolt connection structure is assembled. A part of the axial force will be lost when the bolt is tightened to overcome the assembly clearance, which should be taken into account. The amount of axial force loss caused by the assembly clearance of the traditional bolt connection structure is obtained through the bench test method. Limited by various aspects such as test equipment, test site, and test personnel, the test cycle is long and the result dispersion is large.

[0004] Therefore, a method for determining the amount of axial force loss caused by the assembly clearance of a bolt connection structure is needed to solve the above problems. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for determining the amount of axial force loss caused by the assembly clearance of a bolt connection structure, which can improve the calculation accuracy and speed, and has strong adaptability.

[0006] To achieve this purpose, the present invention adopts the following technical solutions:

[0007] A method for determining the amount of axial force loss caused by the assembly clearance of a bolt connection structure includes the following steps:

[0008] S1. Establish a finite element model for the bolt connection structure;

[0009] S2. Define the relationships between the various parts in the bolt connection structure;

[0010] S3. Calculate the bolt pre-tightening axial force;

[0011] S4. Determine whether there is a non-linear material among the materials used for the various parts in the bolt connection structure. If so, proceed to the next step;

[0012] S5. Define the non-linear material properties;

[0013] S6. Define the boundary conditions of each part in the bolt connection structure and apply bolt pre-tightening force to the bolt;

[0014] S7. Analyze and calculate the finite element model to obtain the relationship curve between the contact pressure and time of the contact surface of the connected parts in the bolt connection structure;

[0015] S8. Calculate the axial force loss caused by the assembly clearance of the bolt connection structure according to the relationship curve.

[0016] Optionally, in step S1, the assembly positions of the part models in the finite element model are the same as those of the parts in the actual bolt connection structure, and there is no structural interference in the assembly of the part models in the finite element model.

[0017] Optionally, in step S2, the following steps are included:

[0018] S21. Establish the constraint points of the connected parts and fully constrain the connected parts at the same time;

[0019] S22. Establish the bolt pre-tightening section;

[0020] S23. Establish the contact surface between the bolt and the connected parts.

[0021] Optionally, in step S3, the bolt pre-tightening axial force is calculated using the following formula:

[0022]

[0023] where F is the bolt axial force; A 0 — is the minimum cross-sectional area of the bolt (mm2); d 0 — is the diameter of the minimum cross-section of the bolt (mm); d 2 — is the pitch diameter (mm); R P0.2min — is the bolt yield strength, in megapascals (MPa); ν is the utilization rate of the bolt yield strength; μ Gmin — is the minimum friction coefficient of the thread; P is the pitch.

[0024] Optionally, in step S5, it is expressed using the following formula:

[0025] R t = K(e t ) n , e t = e p + e s ,

[0026] where R t— True stress, in megapascals (MPa); K — Hardening coefficient, which is the true stress when the true strain is equal to 1; n — Strain hardening index, reflecting the ability of the metal material to resist uniform plastic deformation; e t — True strain; e p — True plastic strain; e s — Yield strain, that is, the plastic strain corresponding to the yield strength point.

[0027] Optionally, in step S6, a force is applied to the bolt in increments of a set step pressure until the bolt pre-tightening force is reached.

[0028] Optionally, in step S7, the finite element model is imported into finite element analysis software for analysis and calculation.

[0029] Optionally, during the analysis and calculation process, the geometric nonlinear data and material nonlinear data of each part in the finite element model need to be combined.

[0030] Optionally, in step S8, a contact surface pressure loss curve is obtained according to the relationship curve. When an inflection point appears on the contact surface pressure loss curve, the axial force loss amount caused by the assembly gap of the bolt connection structure is calculated according to the contact pressure corresponding to the inflection point.

[0031] Optionally, the following formula is used to calculate the axial force loss amount caused by the assembly gap of the bolt connection structure:

[0032] Axial force loss amount = (contact pressure corresponding to the inflection point / bolt pre-tightening axial force) × 100%.

[0033] Advantages of the present invention:

[0034] A method for determining the axial force loss amount caused by the assembly gap of a bolt connection structure provided by the present invention, by establishing a finite element model for the bolt connection structure, defining the relationship between each part in the bolt connection structure, calculating the bolt pre-tightening axial force, and applying the bolt pre-tightening force to the bolt while taking into account the non-linear material, obtaining the relationship curve between the contact pressure of the connected parts and time through analysis and calculation, and obtaining the axial force loss amount caused by the assembly gap of the bolt connection structure according to the relationship curve. In this way, there is no need to obtain the axial force loss amount through the bench test method. By using the finite element analysis method, it is possible to quickly check whether the axial force loss amount caused by the assembly gap of the bolt connection structure meets the design requirements, improving the calculation accuracy and calculation speed; in the test verification stage, it can gradually replace the physical bench test of the assembly axial force of the bolt connection structure, greatly shortening the R & D cycle and saving R & D costs. Description of the Drawings

[0035] Figure 1It is a flowchart of a method for determining the amount of axial force loss caused by the assembly clearance of a bolt connection structure according to the present invention;

[0036] Figure 2 It is a schematic diagram of the connection structure between the subframe 1 and the bushing bolt 2 in a method for determining the amount of axial force loss caused by the assembly clearance of a bolt connection structure according to the present invention;

[0037] Figure 3 It is a model diagram of the boundary conditions in the bolt connection structure according to the present invention;

[0038] Figure 4 It is a curve graph of the contact pressure of the contact surface of the connected parts versus time;

[0039] Figure 5 It is a curve graph of the contact surface pressure loss of the bolt connection structure.

[0040] In the figure:

[0041] 1. Subframe; 2. Bushing bolt; 3. Inner bushing sleeve; 4. Bushing nut. Detailed implementation manners

[0042] The technical solution of the present invention will be further described below in conjunction with the drawings and implementation manners. It can be understood that the specific embodiments described herein are only used to explain the present invention, rather than limiting the present invention. Additionally, it should be noted that for the sake of description, only parts related to the present invention are shown in the drawings rather than all of them.

[0043] In the description of the present invention, it should be noted that unless otherwise clearly defined and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection or a detachable connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0044] In the present invention, unless otherwise clearly defined and limited, the first feature being "above" or "below" the second feature may include the direct contact between the first and second features, or may include the situation where the first and second features are not in direct contact but in contact through other features between them. Moreover, the first feature being "above", "over", and "on" the second feature includes that the first feature is directly above and obliquely above the second feature, or merely indicates that the horizontal height of the first feature is higher than that of the second feature. The first feature being "below", "under", and "beneath" the second feature includes that the first feature is directly below and obliquely below the second feature, or merely indicates that the horizontal height of the first feature is lower than that of the second feature.

[0045] In the process of determining the axial force loss caused by the assembly clearance of the bolt connection structure, in order to improve the calculation accuracy and speed, as Figures 1 - 5 shown, the present invention provides a method for determining the axial force loss caused by the assembly clearance of the bolt connection structure. The method for determining the axial force loss caused by the assembly clearance of the bolt connection structure includes the following steps:

[0046] S1. Establish a finite element model for the bolt connection structure;

[0047] S2. Define the relationships between the various parts in the bolt connection structure;

[0048] S3. Calculate the bolt pre-tightening axial force;

[0049] S4. Determine whether there is a non-linear material among the materials used for the various parts in the bolt connection structure. If so, proceed to the next step;

[0050] S5. Define the non-linear material properties;

[0051] S6. Define the boundary conditions for the various parts in the bolt connection structure, and apply the bolt pre-tightening force to the bolt;

[0052] S7. Analyze and calculate the finite element model to obtain the relationship curve between the contact pressure and time of the contact surface of the connected parts in the bolt connection structure;

[0053] S8. Calculate the axial force loss caused by the assembly clearance of the bolt connection structure according to the relationship curve.

[0054] By the above method, there is no need to obtain the axial force loss through the bench test method. By using the finite element analysis method, it is possible to quickly check whether the axial force loss caused by the assembly clearance of the bolt connection structure meets the design requirements, and improve the calculation accuracy and speed; in the test verification stage, it can replace the physical bench test of the assembly axial force of the bolt connection structure, greatly shortening the R & D cycle and saving the R & D cost.

[0055] Optionally, in step S1, the assembly positions of the part models in the finite element model are the same as those of the parts in the actual bolt connection structure, and there is no structural interference in the assembly of the part models in the finite element model. By the above method, the finite element model can effectively reflect the bolt connection structure in reality, thus ensuring the accuracy and effectiveness of the analysis results.

[0056] Optionally, in step S2, it includes the following steps: S21. Establish the constraint points of the connected parts and fully constrain the connected parts at the same time; S22. Establish the bolt pre-tightening section; S23. Establish the contact surface between the bolt and the connected parts. By defining the relationships between the various parts, the relationships between the various parts in the actual bolt connection structure are mapped.

[0057] Optionally, in step S3, the axial force of the bolt pre-tightening is calculated using the following formula:

[0058]

[0059] where F is the axial force of the bolt; A 0 is the minimum cross-sectional area of the bolt (mm2); d 0 is the diameter of the minimum cross-section of the bolt (mm); d 2 is the pitch diameter (mm); R P0.2min is the yield strength of the bolt, in megapascals (MPa); ν is the utilization rate of the bolt yield strength; μ Gmin is the minimum friction coefficient of the thread; P is the pitch. Through the above calculation method, it is possible to take into account the utilization rate of the bolt yield strength, the basic parameters of the bolt, the minimum friction coefficient of the thread, etc., to ensure the accuracy of the calculated axial force of the bolt pre-tightening.

[0060] Optionally, in step S5, it is expressed using the following formula:

[0061] R t = K(e t ) n , e t = e p + e s ,

[0062] where R t is the true stress, in megapascals (MPa); K is the hardening coefficient, which is the true stress when the true strain is equal to 1; n is the strain hardening index, reflecting the ability of the metal material to resist uniform plastic deformation; e t is the true strain; e p is the true plastic strain; e s is the yield strain, that is, the plastic strain corresponding to the yield strength point. Specifically, on the premise of knowing the values of the hardening index K and the strain hardening index n, substituting the yield strength R s into the above formula, the following formula can be obtained.

[0063] R s = K(e p + e s ) n

[0064] At this time, let e p = 0 (for materials with continuous yield) or e p = 0.2% (for materials with discontinuous yield), and the yield strain e s value can be obtained.

[0065] Arbitrarily select a set of continuous true plastic strains e p and substitute them into the above formula to obtain the true stress R tand the true plastic strain e p curve

[0066] Optionally, in step S6, a force is applied to the bolt in increments of a set step pressure until the bolt pre-tightening force is reached. Specifically, in this embodiment, the bolt pre-tightening cross-section is used to apply the force in increments of 1 KN step by step until the calculated bolt pre-tightening axial force is reached.

[0067] Optionally, in step S7, the finite element model is imported into finite element analysis software for analysis and calculation. By using finite element analysis software, it is very convenient to solve the problem. Specifically, the implicit solution method is adopted. At the same time, during the analysis and calculation process, the geometric non-linear data and material non-linear data of each part in the finite element model need to be combined to ensure the accuracy of the solution results.

[0068] Optionally, in step S8, the contact surface pressure loss curve is obtained according to the relationship curve. When the inflection point appears on the contact surface pressure loss curve, the contact pressure corresponding to the inflection point is used to calculate the axial force loss caused by the assembly clearance of the bolt connection structure.

[0069] Optionally, the following formula is used to calculate the axial force loss caused by the assembly clearance of the bolt connection structure:

[0070] Axial force loss = (contact pressure corresponding to the inflection point / bolt pre-tightening axial force) × 100%.

[0071] Specifically, as Figure 2 shown, taking the connection structure of the subframe 1 and the bushing bolt 2 as an example,

[0072] A finite element model including the subframe 1, the bushing bolt 2, the inner bushing sleeve 3 and the bushing nut 4 needs to be established to ensure that the positions of the part models are consistent with the actual assembly positions and there is no structural interference between the parts. Among them, the modeling mesh size of the subframe 1 is 1 - 2 mm, and the second-order tetrahedral element is used; the modeling mesh sizes of the bushing bolt 2 and the inner bushing sleeve 3 are 1 - 2 mm, and the hexahedral element is used, which is obtained by rotating the two-dimensional model, and a good contact effect on the contact surface can be ensured; the mesh size of the bushing nut 4 is 2 - 3 mm, and the hexahedral element is used. a Define the sliding contact relationship between the bushing bolt 2, the bushing nut 4 and the subframe 1; b Define the gap Δ between the inner bushing sleeve 3 and the subframe 1 to be consistent with the actual assembly gap; c Define the sliding contact relationship between both ends of the inner bushing sleeve 3 and the subframe 1.

[0073] As Figure 3 shown, d Establish the constraint points of the subframe 1; e Establish the pre-tightening cross-section of the bushing bolt 2 and apply the bolt pre-tightening axial force; f Establish the contact surface between the bushing bolt 2 and the subframe 1 and output the contact surface pressure CFN; g Establish the contact surface between the subframe 1 and the inner bushing sleeve 3 and output the contact surface pressure CFN.

[0074] As shown Figure 4 in FIG., in step S7, a relationship curve of the contact surface pressure CFN (N) between the output bushing bolt 2 and the subframe 1 and time (s) is output. Since there is an assembly gap in the bolt connection structure, the axial force of the bolt is lost due to overcoming the assembly gap, and a relationship curve of the contact surface pressure CFN (N) between the subframe 1 and the inner bushing sleeve 3 and time (s) is output.

[0075] On the basis of step S7, a relationship curve of the difference between the contact surface pressure CFN (N) between the bushing bolt 2 and the subframe 1 and the contact surface pressure CFN (N) between the subframe 1 and the inner bushing sleeve 3 and time (s) is the contact surface pressure loss curve, as shown in Figure 5 . This curve has two stages. The first stage is the stage where the axial force is lost due to the assembly gap: in this stage, since there is an assembly gap between the subframe 1 and the inner bushing sleeve 3, the contact surface pressure is zero, and the bolt pre-tightening axial force is lost due to overcoming the assembly gap until the assembly gap is eliminated when the inflection point of the contact surface pressure loss curve appears; the second stage is the stage where the axial force is lost due to the structural embedding deformation: when the inflection point of the contact surface pressure loss curve appears, that is, when the assembly gap is eliminated, the axial force loss is mainly caused by the deformation of the components themselves, and it enters the stage where the axial force is lost due to the structural embedding deformation. It is defined that the axial force loss caused by the assembly gap of the bolt connection structure = (the loss amount at the inflection point of the contact surface pressure loss curve / the bolt pre-tightening axial force) × 100%. It is required that the axial force loss caused by the assembly gap of the bolt connection structure should meet the design requirements.

[0076] Obviously, the above embodiments of the present invention are only examples for clearly explaining the present invention, and are not intended to limit the embodiments of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made on the basis of the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. A method for determining the amount of axial force loss caused by the assembly clearance of a bolt connection structure, characterized in that, it includes the following steps: S1. Establish a finite element model for the bolt connection structure; S2. Define the relationships between the various parts in the bolt connection structure; S3. Calculate the bolt pre-tightening axial force; S4. Determine whether there is a non-linear material among the materials used for the various parts in the bolt connection structure. If so, proceed to the next step; S5. Define the non-linear material properties; S6. Define the boundary conditions for the various parts in the bolt connection structure, and apply the bolt pre-tightening force to the bolt; S7. Analyze and calculate the finite element model to obtain the relationship curve between the contact pressure and time of the contact surface of the connected parts in the bolt connection structure; S8. Calculate the amount of axial force loss caused by the assembly clearance of the bolt connection structure according to the relationship curve; In step S8, obtain the contact surface pressure loss curve according to the relationship curve. When the contact surface pressure loss curve has an inflection point, calculate the amount of axial force loss caused by the assembly clearance of the bolt connection structure according to the contact pressure corresponding to the inflection point.

2. A method for determining the amount of axial force loss caused by the assembly clearance of a bolt connection structure according to claim 1, characterized in that, in step S1, the assembly positions of the part models in the finite element model are the same as the assembly positions of the various parts in the actual bolt connection structure, and there is no structural interference in the assembly of the part models in the finite element model.

3. A method for determining the amount of axial force loss caused by the assembly clearance of a bolt connection structure according to claim 1, characterized in that, step S2 includes the following steps: S21. Establish constraint points for the connected parts and fully constrain the connected parts at the same time; S22. Establish a bolt pre-tightening section; S23. Establish the contact surface between the bolt and the connected parts.

4. A method for determining the amount of axial force loss caused by the assembly clearance of a bolt connection structure according to claim 1, characterized in that, in step S3, the bolt pre-tightening axial force is calculated using the following formula: Among them, F—the axial force of the bolt; A 0 —the minimum cross-sectional area of the bolt; d 0 —the diameter of the minimum cross-section of the bolt; d 2 —the pitch diameter of the thread; R P0.2min —the yield strength of the bolt; ν—the utilization rate of the bolt yield strength; μ Gmin — Minimum coefficient of friction of the thread; P — Pitch.

5. A method for determining the amount of axial force loss caused by the assembly clearance of a bolt connection structure according to claim 1, characterized in that, in step S5, it is represented by the following formula: R t = K(e t ) n , e t = e p + e s , Among them, R t — True stress; K — hardening coefficient, which is the true stress when the true strain is equal to 1; n — strain hardening index, reflecting the ability of the metal material to resist uniform plastic deformation; e t — True strain; e p — True plastic strain; e s — Yield strain, that is, the plastic strain corresponding to the yield strength point.

6. A method for determining the amount of axial force loss caused by the assembly clearance of a bolt connection structure according to claim 1, characterized in that, in step S6, apply a force to the bolt in increments of a set step pressure until the bolt pre-tightening force is reached.

7. A method for determining the amount of axial force loss caused by the assembly clearance of a bolt connection structure according to claim 1, characterized in that, in step S7, import the finite element model into a finite element analysis software for analysis and calculation.

8. A method for determining the amount of axial force loss caused by the assembly clearance of a bolt connection structure according to claim 7, characterized in that, during the analysis and calculation process, it is necessary to combine the geometric non-linear data and material non-linear data of the various parts in the finite element model.

9. A method for determining the amount of axial force loss caused by the assembly clearance of a bolt connection structure according to claim 1, It is characterized in that the following formula is used to calculate the loss of axial force caused by the assembly clearance of the bolt connection structure: Axial force loss = (contact pressure corresponding to the inflection point / bolt pre-tightening axial force) × 100%.

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