Bolt joint interface contact force measuring method

Abstract

The invention discloses a method for measuring the interface contact force of a bolt joint, which comprises the following steps of: establishing a relational expression between the contact surface area of a bolt and a base material and the interface contact force of the bolt joint according to different bolt thread types, and associating the interface contact force of the bolt joint with electric contact to construct a bolt thread force-electric contact model; the interface contact force of the bolt joint can be calculated through easily obtained physical parameters, so that the contact force distribution of the connecting piece can be quickly and effectively analyzed and measured, and meanwhile, the use condition of the connecting piece is evaluated.

Description

Technical Field

[0001] The invention belongs to the field of bolt design, and in particular relates to a method for measuring contact force at a bolt joint interface. Background Art

[0002] The contact characteristics of mechanical assembly interfaces have a significant impact on the sustained construction and rapid development of major national projects such as aerospace, ocean development, deep space exploration, and large scientific facilities in my country, and are key to ensuring the performance of mechanical equipment and the safety of mechanical use. Taking bolted joints as an example, performance degradation may occur during use. For example, when subjected to extreme external loads, bolted joints cannot maintain their predetermined tightening state, thereby losing their proper connection function. In severe cases, this may even lead to equipment damage or safety accidents. The contact force at the contact interface of a bolted joint directly affects the fatigue strength and connection retention of the bolt itself. Excessive contact force will cause microcracks or even rupture of the assembled component. Therefore, the key to the degradation of bolted connection performance lies in the change in the contact force state at the contact interface, which leads to a change in its contact state. How to measure the contact force and evaluate the status of structural parts in order to detect dangerous areas as early as possible, quickly and effectively analyze and determine the contact force distribution of the connecting parts, and at the same time evaluate the usage status of the connecting parts has become an urgent problem to be solved. Therefore, the accurate calculation of the contact force at the contact interface of bolted joints is the basis and key to ensuring and improving the connection performance of assembly components.

[0003] Existing rough contact theories all adopt certain simplifications and assumptions, such as rigid plane-rough surface contact and uniform ball contact. These contact models reveal the rough interface contact mechanism to a certain extent. However, due to the limitations of model assumptions and simplifications, it is difficult to develop them into effective measurement methods for complex bolt configurations. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for measuring the interface contact force of a bolt joint to solve the problems raised by the above background technology.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for measuring the contact force of a bolt joint interface, comprising the following steps: S1: Confirm the bolt thread form and measure the bolt tooth angle , elastic modulus of the bolt , elastic modulus of the substrate , bolt radius , and the substrate through-hole radius , Poisson's ratio of the bolt , Poisson's ratio of the substrate , contact resistance between bolt and base material , substrate resistivity , thread height ; S2: When the bolt is connected to the substrate, the positive pressure on the bolt in the substrate through hole is marked as , according to different thread types, substitute the data obtained in step S1 into the following formula to calculate ,in: Triangular thread bolts: ; Trapezoidal thread bolts: ; Serrated thread bolts: ; Where, is the equivalent radius of contact between the major diameter of the bolt and the through hole of the substrate, is the crest width of the trapezoidal thread bolt, Sawtooth thread bolt crest width, and They are the tooth angles on both sides of the serrated thread bolt, is the equivalent elastic modulus; By formula: Calculated, By formula: Calculated.

[0006] Preferably, in step S1, the contact resistance between the bolt and the substrate is measured. When the voltage between the bolt and the substrate is measured, electrodes are set on the bolt and the substrate. and current I, through the formula , the contact resistance between the bolt and the substrate is calculated .

[0007] Compared with the prior art, the present invention has the following beneficial effects: The present invention establishes a relationship between the contact surface area of the bolt and the substrate and the positive pressure exerted on the bolt when connected to the substrate (i.e., the interfacial contact force of the bolt joint) based on different bolt thread types, and links the interfacial contact force of the bolt joint with the electrical contact to build a bolt thread force-electrical contact model. The interfacial contact force of the bolt joint can be calculated by measuring easily accessible physical parameters, thereby enabling rapid and effective analysis and measurement of the contact force distribution of the connector, while also evaluating the usage status of the connector. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 Schematic diagram of contact force at the bolt joint interface provided by an embodiment of the present invention; Figure 2 Schematic diagram of the contact between the triangular thread in the axial direction and the substrate provided by an embodiment of the present invention; Figure 3This is a schematic diagram of the contact between the axial trapezoidal thread and the substrate provided by an embodiment of the present invention; Figure 4 Schematic diagram of the contact between the axial serrated thread and the substrate provided by an embodiment of the present invention; Figure 5 Schematic diagram of circumferential contact between a bolt and a substrate provided by an embodiment of the present invention; Figure 6 1. A diagram comparing the calculated and actual values of the contact force at the interface of a triangular threaded bolt provided by an embodiment of the present invention; Figure 7 1. This is a comparison diagram of the calculated and actual values of the contact force on the interface of a serrated threaded bolt provided by an embodiment of the present invention; Figure 8 1 is a schematic diagram of contact resistance measurement provided by an embodiment of the present invention; In the figure, 1-bolt, 2-base material, 3-contact surface. DETAILED DESCRIPTION

[0009] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0010] The present invention provides a technical solution: a method for measuring the contact force of a bolt joint interface, which is based on a simplified surface force-electrical contact model, introduces spiral configuration parameters, and establishes a method for measuring the contact force distribution of a spiral surface.

[0011] First, any processed plane has a rough surface. For the contact between the thread 1 and the through-hole wall of the substrate 2, only some raised points or smaller contact surfaces are in real contact on the contact surface 3. Therefore, when the current flows from one conductor to another, it can only flow through these contact points or small cross-sections, thus forming a current contraction. This current contraction generates a contraction resistance, i.e., the contact resistance. The relationship between the contact resistance and the contact area is shown in Formula 1: (1) Where, is the contact resistance, is the substrate resistivity, is the contact depth. In the contact model between the bolt and the through hole of the substrate, is the thread height of the bolt, is the contact area between the thread and the substrate hole wall.

[0012] When bolt 1 is used to connect substrate 2, the thread is mainly in contact with the hole wall. At this time, bolt 1 is mainly subjected to shear force, such as Figure 1 As shown, at this time, the contact between the thread and the hole wall is mainly positive pressure. When solving the contact area between the thread and the hole wall, the thread is considered to be the roughness of the bolt 1 surface. The contact area between the thread and the hole wall can be decomposed into two directions, such as Figure 2-Figure 5 As shown, that is, in the axial and circumferential directions, the actual contact area can be considered as the product of the axial contact line length and the circumferential contact line length; Based on this, a relationship is established between the contact surface area of bolt 1 and substrate 2 and the normal pressure exerted on bolt 1 when connected to substrate 2 (i.e., the interfacial contact force of the bolt joint). The interfacial contact force of bolt 1 is then linked to electrical contact, and a bolt thread force-electrical contact model is constructed. The interfacial contact force of the bolt joint can be calculated by measuring readily available physical parameters. The force-electrical contact models for different threaded bolts are as follows: Triangular threaded bolt force-electrical contact model: (2) By performing simultaneous calculations on formula (2), we can obtain: (3) Where A is the contact area, is the contact force at the bolt joint interface, is the axial contact line length between the bolt thread and the substrate through hole, is the circumferential contact line length between the thread and the substrate through hole, is the equivalent radius of contact between the major diameter of the bolt and the through hole of the substrate, is the tooth angle of the triangular thread, is the equivalent elastic modulus.

[0013] Substituting (3) into (1) we finally get: (4) Trapezoidal thread bolt force-electrical contact model: (5) Combining formula (5) together, we can get: (6) Where A is the contact area, is the contact force at the bolt joint interface, is the axial contact line length between the bolt thread and the substrate through hole, is the circumferential contact line length between the thread and the substrate through hole, is the equivalent radius of contact between the major diameter of the bolt and the through hole of the substrate, is the crest width of the trapezoidal thread bolt, It is the tooth angle of trapezoidal thread.

[0014] Substituting (6) into (1) we finally get: (7) Serrated thread bolt force-electrical contact model: (8) By performing simultaneous calculations on formula (8), we can obtain: (9) Where A is the contact area, is the contact force at the bolt joint interface, is the axial contact line length between the bolt thread and the substrate through hole, is the circumferential contact line length between the thread and the substrate through hole, is the equivalent radius of contact between the major diameter of the bolt and the through hole of the substrate, Sawtooth thread bolt crest width, and They are the tooth angles on both sides of the serrated thread bolt.

[0015] Substituting (9) into (1) we finally get: (10) In formula (4), formula (7), and formula (10), Calculated by formula (11), Calculated by formula (12); (11) In formula (11), is the elastic modulus of the bolt, is the elastic modulus of the substrate, is the Poisson's ratio of the bolt, is the Poisson's ratio of the substrate, which can be obtained by querying the material parameter data.

[0016] (12) In formula (12), is the bolt radius, is the radius of the substrate through hole.

[0017] In the specific implementation process, by measuring the thread angle of the bolt 1 and the elastic modulus of the bolt 1 , elastic modulus of substrate 2 、Bolt 1 radius , substrate through-hole radius , Poisson's ratio of bolt 1 , Poisson's ratio of substrate 2 , contact resistance between bolt 1 and substrate 2 , substrate 2 resistivity , thread height The interface contact force of the bolt joint can be calculated by substituting the value into the force-electric contact model corresponding to the thread of bolt 1.

[0018] In this embodiment, shear force is applied to triangular thread bolts and serrated thread bolts respectively to simulate the interface contact force of bolt 1 in the through hole of substrate 2 when the bolt is connected to the substrate. The interface contact force of the bolt joint calculated by the force-electric contact model is compared with the actual applied force. The results are as follows: Figure 6 and Figure 7 As shown, the bolt joint interface contact force calculated by the bolt joint interface contact force measurement method of the present invention is consistent with the actual interface contact force.

[0019] In this embodiment, when measuring the contact resistance between the bolt 1 and the substrate 2 When the electrodes A, M, N, and B are set on the bolt 1 and the substrate 2, the electrodes A and B supply current, and the electrodes M and N measure the voltage of the contact surface. The electrode connection method is as follows: Figure 8 As shown, by measuring the voltage across bolt 1 and substrate 2 and current I, through the formula , the contact resistance between bolt 1 and substrate 2 is calculated .

[0020] In this embodiment, the material parameters of the bolts and the base material are shown in Table 1 below. Table 1 Material parameters of bolts and base materials

[0021] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for measuring the contact force of a bolt joint interface, characterized in that: The following steps are involved: S1: Confirm the bolt thread form and measure the bolt tooth angle , elastic modulus of the bolt , elastic modulus of the substrate , bolt radius , and the substrate through-hole radius , Poisson's ratio of the bolt , Poisson's ratio of the substrate , contact resistance between bolt and base material , substrate resistivity , thread height ; S2: When the bolt is connected to the substrate, the positive pressure on the bolt in the substrate through hole is marked as , according to different thread types, substitute the data obtained in step S1 into the following formula to calculate ,in: Triangular thread bolts: ; Trapezoidal thread bolts: ； Serrated thread bolts: ； Where, is the equivalent radius of contact between the major diameter of the bolt and the through hole of the substrate, is the crest width of the trapezoidal thread bolt, Sawtooth thread bolt crest width, and They are the tooth angles on both sides of the serrated thread bolt, is the equivalent elastic modulus; By formula: Calculated, By formula: Calculated.

2. The method for measuring the contact force of the bolt joint interface according to claim 1, characterized in that: In step S1, the contact resistance between the bolt and the substrate is measured. When the voltage between the bolt and the substrate is measured, electrodes are set on the bolt and the substrate. and current I, through the formula , the contact resistance between the bolt and the substrate is calculated .

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