A method and system for characterizing multi-parameter evolution process of a bolted joint interface

Abstract

The present application belongs to the technical field of mechanical structure performance test, and discloses a bolted joint interface multi-parameter evolution process characterization method and system. The method comprises the following steps: test sample assembly preparation and initial surface topography test; evolution process cyclic loading and synchronous data acquisition; joint interface multi-parameter evolution process online characterization; joint interface topography parameter detection after loading; real contact ratio extraction and evolution result output. The system comprises a test sample assembly, a pretightening force measuring assembly, a cyclic load loading assembly, a cyclic load measuring assembly, a system fixed base assembly, a relative displacement measuring assembly and a sensor tooling assembly. The bolted joint interface multi-parameter evolution process characterization method solves the problem of parameter evolution process calculation distortion in theoretical modeling to a great extent, and can more comprehensively reveal the evolution laws of contact, sliding, energy dissipation, pretightening force attenuation and stiffness degradation of the bolted joint interface under cyclic load.

Description

Technical Field

[0001] This invention belongs to the field of mechanical structure performance testing technology, and relates to a method and system for characterizing the multi-parameter evolution process of bolted joint surfaces. Background Technology

[0002] High-strength bolted connections are indispensable basic fastening units in high-end equipment such as aerospace, CNC machine tools, and rail transportation. During service, bolted connections typically bear complex alternating loads, such as transverse shear loads and longitudinal tensile and compressive loads. Under long-term alternating loads, the irreversible degradation of the mechanical properties of the joint surface is a fatal hidden danger that can lead to problems such as decreased equipment accuracy, sealing leaks, and even structural failure. The root cause of the degradation of the mechanical properties of the joint surface is controlled by the dynamic evolution of microscopic contact parameters. Therefore, this paper proposes a method for characterizing the evolution process of the main contact parameters of bolted joint surfaces, providing a basis for evaluating the connection performance, analyzing degradation mechanisms, predicting service life, and optimizing the structural design of bolted connections.

[0003] In 2017, Huang Yumei et al. from Xi'an University of Technology disclosed a testing device and method for the normal basic characteristic parameters of mechanical mating surfaces in patent CN201711458850.6. Based on measured excitation force, relative displacement, and acceleration, they provided calculation methods for the static stiffness, dynamic stiffness, and damping of the mating surfaces. In 2021, Sun Yunyun et al. from Wuhan University disclosed a method for calculating the true contact rate of bolt mating surfaces with micron-level roughness in patent CN202110960926.5. Based on molecular dynamics and contact mechanics, they established a single roughness peak contact model, realizing a direct correlation between bolt preload and the true contact rate of the bolted structure surface. In 2024, Liu Zhifeng et al. from Jilin University disclosed a method for calculating the static friction coefficient of mating surfaces under microscopic contact in patent CN202411944051.X. This method considered the interaction between micro-protrusions and the matrix, as well as the three stages of material elasticity, elastoplasticity, and complete plastic deformation, and established a surface static friction coefficient model based on fractal theory. In 2025, Hong Jun et al. from Xi'an Jiaotong University disclosed a method and system for calculating the dynamic contact stiffness and damping of the assembly mating surface considering anisotropy in patent CN202511145896.7. The method calculates the contact stiffness and damping of the mating surface under dynamic disturbance based on the static contact load and disturbance displacement of all micro-convex contact pairs.

[0004] Although the aforementioned existing technologies have studied the contact parameters of bolted joint surfaces from different perspectives, including theoretical modeling and practical testing, they still have the following shortcomings: First, most existing technologies focus on parameter testing under initial or stable conditions, making it difficult to reflect the dynamic changes in contact parameters throughout their entire lifecycle due to the degradation of joint surface performance under service conditions. Second, for the study of actual contact rates, existing technologies mostly rely on idealized theoretical models and numerical simulations. While these methods can obtain estimates of the contact state under certain conditions, they are usually quite sensitive to simplifications of surface morphology, assumptions about material models, contact boundary conditions, and load transfer methods. Especially after bolted joint surfaces have undergone cyclic loading, irreversible changes such as wear, crushing, and slippage have occurred at the interface, making it difficult for theoretical models to effectively characterize the actual contact state of the interface at this time, thus leading to distorted contact rate calculation results. Third, most existing technologies focus on single or a few parameters, lacking the ability to characterize the multi-parameter synergy and continuous evolution of the main contact parameters of bolted joint surfaces throughout the entire process. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for characterizing the multi-parameter evolution process of bolted joint surfaces.

[0006] The technical solution of this invention: A method for characterizing the multi-parameter evolution process of bolted joint surfaces includes the following steps: Step 1, Preparation and Initial Surface Morphology Testing of Test Sample Component 1: Based on the actual connection structure of the equipment, test sample component 1 with bolted joint surface is prepared, ensuring that the processing technology, bolted joint surface material, and surface roughness of test sample component 1 are consistent with the actual connection structure; a fixed observation window is marked in the test area of ​​test sample component 1, and the surface density of micro-protrusions, the average radius of curvature of micro-protrusions, the highest peak value of surface micro-protrusions, the probability density function of true surface height, and the initial support rate curve of the surface morphology before the test are obtained in the fixed observation window; the bolted joint surface is assembled according to the preset preload, and after assembly, it is left to stand until the initial creep of test sample component 1 stabilizes, and the initial preload of test sample component 1 is recorded; The fixed observation window is located in the annular contact area around the bolt through hole; The horizontal axis of the initial support rate curve represents the support rate. mr The vertical axis represents the surface height. z support rate mr To the corresponding surface height z The percentage of the area of ​​the micro-protrusion to the total area of ​​the bolted joint surface; Step 2, Evolution process cyclic loading and synchronous data acquisition: Apply normal cyclic load and tangential cyclic load to test sample component 1, and synchronously and in real time acquire the normal relative displacement, tangential relative displacement, normal load, tangential load and preload of bolted joint surface in each loading cycle until the number of loading cycles reaches the preset value. Step 3, Online characterization of the multi-parameter evolution process of the joint surface: The normal relative displacement, tangential relative displacement, normal load, tangential load, and preload of the bolted joint surface in each loading cycle are processed separately. Based on the tangential load and tangential relative displacement in the loading cycle, a tangential load-displacement hysteresis loop is plotted. Based on the normal load and normal relative displacement in the loading cycle, a normal load-displacement hysteresis loop is plotted. Based on the tangential load-displacement hysteresis loop and the normal load-displacement hysteresis loop, the residual preload, tangential equivalent contact stiffness, normal equivalent contact stiffness, equivalent loss factor, and friction coefficient are calculated cycle by cycle. Then, an evolution process function of the residual preload, tangential equivalent contact stiffness, normal equivalent contact stiffness, equivalent loss factor, and friction coefficient is established as the number of loading cycles accumulates. No. N Residual preload corresponding to each loading cycle Defined as the cycle period T Internal instantaneous preload Time average: In the formula, t is the sampling time of the instantaneous preload; No. N Tangential equivalent contact stiffness corresponding to each loading cycle Secant stiffness characterization is based on the extreme points of the tangential load-displacement hysteresis loop: No. N Normal equivalent contact stiffness corresponding to each loading cycle Secant stiffness characterization is based on the extreme points of the normal load-displacement hysteresis loop: In the formula, and The first N The maximum and minimum values ​​of the tangential load within each loading cycle. and The first N The maximum and minimum values ​​of the tangential relative displacement within each loading cycle. and The first N The maximum and minimum values ​​of the normal load within each loading cycle. and The firstN The maximum and minimum values ​​of the normal relative displacement within each loading cycle; No. N Equivalent loss factor corresponding to each loading cycle Defined as the energy dissipated during the loading cycle With maximum elastic strain energy The ratio: Among them, dissipated energy Calculation of the area of ​​the tangential load-displacement hysteresis loop formed by the tangential load and the relative tangential displacement: In the formula, denoted as tangential relative displacement of the bolted joint surface, and denoted as the abscissa of the tangential load-displacement hysteresis loop. The tangential load borne by the bolted joint surface is represented by the ordinate of the tangential load-displacement hysteresis loop. Among them, the maximum elastic strain energy The area is obtained by using the right triangle formed by the amplitude of the tangential load and the amplitude of the tangential displacement: No. N Friction coefficient corresponding to each loading cycle Defined as the frictional force during the global slip phase within this loading cycle. With residual preload The ratio: The global slip phase is the slip phase corresponding to the tangential load-displacement hysteresis loop entering the force plateau segment; the tangential relative displacement of the bolted joint surface is taken. At that time, the ordinate of the tangential load-displacement hysteresis loop corresponds to and The mean of absolute values ​​is used as friction force , ; Step 4, Post-loading combined with surface morphology parameter detection: When the number of loading cycles reaches the preset value, stop the test, remove the bolts of test sample component 1, clean the connected parts, and then reposition and scan the same fixed observation window marked in Step 1 to obtain the surface morphology of the final state, including the surface density of micro-protrusions, the average radius of curvature of micro-protrusions, the highest peak value of surface micro-protrusions, the probability density function of the true height of the surface, and the final support rate curve. Step 5, Extraction and Evolution Results of Actual Contact Rate: Substitute the initial preload recorded in Step 1 into the normal force integral equation of the discretized Greenwood-Williamson model to obtain the elastic equivalent separation distance of the initial state. Then, substitute the elastic equivalent separation distance of the initial state into the initial support rate curve obtained in Step 1 for interpolation mapping to obtain the actual contact rate of the initial state joint surface. Align the final support rate curve obtained in Step 4 with the initial support rate curve in the deep valley region to obtain the equivalent separation distance of the final state. Then, substitute the equivalent separation distance of the final state into the initial support rate curve for interpolation mapping to obtain the actual contact rate of the final state joint surface. Correlate the actual contact rate of the initial state joint surface and the actual contact rate of the final state joint surface with the evolution process function established in Step 3, which accumulates with the number of loading cycles, including residual preload, tangential equivalent contact stiffness, normal equivalent contact stiffness, equivalent loss factor, and friction coefficient, to obtain the characterization results of the multi-parameter evolution process of the bolted joint surface. The integral equation for the normal force is: In the formula, This is the initial preload. The initial elastic equivalent separation distance. , and These are the surface density of the micro-protrusions, the average radius of curvature of the micro-protrusions, and the highest peak value of the surface micro-protrusions extracted in step one, respectively. The total area of ​​the mating surfaces. The probability density function of the true surface height extracted in step one. It is the equivalent elastic modulus and satisfies the following conditions: in, and These are the Young's moduli of the two connecting parts that constitute the test specimen assembly (1), respectively. and These are the Poisson's ratios of the materials of the two connectors, respectively. The elastic equivalent separation distance of the initial state Substituting the values ​​into the initial support ratio curve and performing interpolation mapping, we obtain the true contact ratio of the initial state interface. ; Equivalent separation distance of the final state The final support rate curve is obtained by aligning the troughs of the initial support rate curve with the troughs of the troughs. mr >80% of the deep valley tail area is overlapped and aligned, and its vertical absolute translation amount The amount of physical damage to the surface, and the equivalent separation distance in the final state. The equivalent separation distance of the final state Substitute the values ​​back into the initial support ratio curve for interpolation mapping to obtain the true contact ratio of the final state interface. .

[0007] A multi-parameter evolution process characterization system for bolted joint surfaces includes a test specimen assembly 1, a preload measurement assembly 2, a cyclic load loading assembly 3, a cyclic load measurement assembly 4, a system fixing base assembly 5, a relative displacement measurement assembly 6, and a sensor tooling assembly 7. The preload measuring component 2 is fixed between the nut and the connected part of the test sample component 1. The test sample component 1 is clamped on the cyclic load loading component 3 by a hydraulic chuck. The cyclic load measuring component 4 is fixed on the cyclic load loading component 3 by bolts. The two are connected in series and fixed on the system fixed base component 5. The relative displacement measuring component 6 is fixed on the sensor tooling component 7 by bolts. The sensor tooling component 7 is fixed on the system fixed base component 5 by bolts.

[0008] The beneficial effects of this invention are: (1) This invention provides a method for characterizing the evolution of the main contact parameters of a bolted joint surface throughout its entire life cycle, which realizes continuous, dynamic and quantitative characterization of the bolted joint surface throughout its service life, and can more comprehensively reveal the behavior of the bolted joint surface under cyclic loads, such as interface slip and energy dissipation.

[0009] (2) This invention proposes a strategy for obtaining the true contact rate based on the support ratio curve. By combining the measured surface morphology parameters, the support ratio curve and the solution of the normal force integral, the quantitative extraction of the true contact rate of the initial and final states of the interface is realized. This solves the problem of distortion in the theoretical calculation of the contact rate after the interface is damaged by loading, and improves the accuracy and reliability of the true contact rate characterization.

[0010] (3) This invention combines the characterization of the evolution process of the main contact parameters with the extraction of the actual contact rate, which can simultaneously reflect the macroscopic mechanical response and the microscopic actual contact state of the bolted joint surface, providing a basis for the performance evaluation, degradation mechanism analysis, life prediction and structural optimization design of bolted structures. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the process for characterizing the multi-parameter evolution of bolted joint surfaces; Figure 2 This is a schematic diagram of the parameter measurement part of the system characterizing the multi-parameter evolution process of the bolted joint surface.

[0012] Figure 3 This is a schematic diagram of the load loading part of the system, which characterizes the multi-parameter evolution process of the bolted joint surface.

[0013] In the figure: 1 Test specimen assembly; 2 Preload measurement assembly; 3 Cyclic load loading assembly; 4 Cyclic load measurement assembly; 5 System fixed base assembly; 6 Relative displacement measurement assembly; 7 Sensor tooling assembly. Detailed Implementation

[0014] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0015] Taking the characterization of the contact parameter evolution process of a typical bolted joint surface sample of a machine tool as an example, step one is the preparation of the test sample component 1 and the initial surface morphology test; First, taking the machine tool bed-guide rail mating surface as the research object, a test sample assembly 1 of the bolted mating surface was prepared. The two connected parts were made of 45 steel and HT200 gray cast iron, respectively. The fasteners were M10, 10.9 grade high-strength bolts, and the surface processing technology was milling. The surface roughness of both was Ra=1.6μm, and the nominal contact area was 50×50mm. Then, a fixed observation window was marked in the annular core contact area around the bolt through hole. A white light interferometer was used to obtain the surface density of micro-protrusions, the average radius of curvature of micro-protrusions, the highest peak value of surface micro-protrusions, the probability density function of the true surface height, and the initial support rate curve of the surface morphology before the test at the fixed observation window. Finally, the preload measuring component 2 was fixed between the nut and the connected parts of the test sample assembly 1. The test sample assembly 1 was assembled with a preload of 10kN. After assembly, it was left to stand for 1 hour. After the value of the preload measuring component 2 stabilized, the initial preload was recorded. .

[0016] Step two: Cyclic loading and synchronous data acquisition during the evolution process; The test specimen assembly 1 is clamped onto the cyclic load loading assembly 3 by a hydraulic chuck. A sinusoidal normal cyclic load and a sinusoidal tangential cyclic load with an amplitude of 10kN and a frequency of 10Hz are applied to the test specimen. The preload measuring assembly 2, the cyclic load measuring assembly 4, and the relative displacement measuring assembly 6 are used to synchronously and in real time collect the normal relative displacement, tangential relative displacement, normal load, tangential load, and preload of the bolted joint surface in each loading cycle until the test is stopped after 360,000 cycles.

[0017] Step 3: Online characterization of the multi-parameter evolution process; The normal relative displacement, tangential relative displacement, normal load, tangential load, and preload collected in each loading cycle are processed separately, and tangential load-displacement hysteresis loops and normal load-displacement hysteresis loops are plotted. Based on the tangential load-displacement hysteresis loops and normal load-displacement hysteresis loops, the residual preload, tangential equivalent contact stiffness, normal equivalent contact stiffness, equivalent loss factor, and friction coefficient are calculated cycle by cycle. Then, the evolution process function of residual preload, tangential equivalent contact stiffness, normal equivalent contact stiffness, equivalent loss factor, and friction coefficient with the number of loading cycles is established. The residual preload is calculated cycle by cycle using equation (1): (1) The tangential equivalent contact stiffness is calculated cycle by cycle using equation (2): (2) The normal equivalent contact stiffness is calculated periodically using equation (3): (3) The equivalent loss factor is calculated periodically using equations (4) to (6): (4) (5) (6) The friction coefficient is calculated cycle by cycle using equations (7) to (8): (7) (8) Step 4: After loading, perform surface topography parameter detection; The test was stopped after the number of cyclic loading cycles reached 360,000. The bolts were removed, and the connected parts were cleaned with an ultrasonic cleaner. The same fixed observation window marked in step one was repositioned and scanned. A white light interferometer was used to obtain the surface density of the micro-protrusions, the average radius of curvature of the micro-protrusions, the highest peak value of the surface micro-protrusions, the probability density function of the true height of the surface, and the final support rate curve of the final state surface morphology. Step 5: Extract the actual contact rate and output the evolution results; Record the initial preload in step one. Substituting into formula (9), the initial elastic equivalent separation distance can be solved inversely. : (9) The elastic equivalent separation distance of the initial state Substituting the initial support rate curve obtained in step one into the interpolation curve, the actual contact rate of the initial state interface is found to be 48.2%. Compare the final support rate curve obtained in step four with the initial support rate curve obtained in step one. mr >80% of the deep valley tail area was overlapped and aligned to obtain the vertical absolute translation amount. Then the equivalent separation distance of the final state The equivalent separation distance of the final state Substituting the data back into the initial support rate curve for interpolation mapping, we obtain the final true contact rate of the interface as 71.3%.

[0018] By correlating the actual contact rate of the initial state joint surface and the actual contact rate of the final state joint surface with the evolution process function established in step three, the multi-parameter evolution process characterization results of the bolted joint surface are obtained.

[0019] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features, and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for characterizing the multi-parameter evolution process of a bolted joint surface, characterized in that, Includes the following steps: Step 1, Preparation of test sample assembly (1) and initial surface morphology test: Based on the actual connection structure of the equipment, prepare test sample assembly (1) with bolted joint surface, so that the processing technology, bolted joint surface material and surface roughness of test sample assembly (1) are consistent with the actual connection structure; mark fixed observation windows in the test area of ​​test sample assembly (1), and obtain the surface density of micro-protrusions, average radius of curvature of micro-protrusions, highest peak value of surface micro-protrusions, probability density function of true surface height and initial support rate curve of surface morphology before test in the fixed observation window; complete the assembly of bolted joint surface according to preset preload, and after assembly, let it stand. After the initial creep of test sample assembly (1) stabilizes, record the initial preload of test sample assembly (1); The fixed observation window is located in the annular contact area around the bolt through hole; The horizontal axis of the initial support rate curve represents the support rate. mr The vertical axis represents the surface height. z support rate mr To the corresponding surface height z The percentage of the area of ​​the micro-protrusion to the total area of ​​the bolted joint surface; Step 2, Evolution process cyclic loading and synchronous data acquisition: Apply normal cyclic load and tangential cyclic load to the test sample component (1), and synchronously and in real time acquire the normal relative displacement, tangential relative displacement, normal load, tangential load and preload of the bolted joint surface in each loading cycle until the number of loading cycles reaches the preset value; Step 3, Online characterization of the multi-parameter evolution process of the joint surface: The normal relative displacement, tangential relative displacement, normal load, tangential load, and preload of the bolted joint surface in each loading cycle are processed separately. Based on the tangential load and tangential relative displacement in the loading cycle, a tangential load-displacement hysteresis loop is plotted. Based on the normal load and normal relative displacement in the loading cycle, a normal load-displacement hysteresis loop is plotted. Based on the tangential load-displacement hysteresis loop and the normal load-displacement hysteresis loop, the residual preload, tangential equivalent contact stiffness, normal equivalent contact stiffness, equivalent loss factor, and friction coefficient are calculated cycle by cycle. Then, an evolution process function of the residual preload, tangential equivalent contact stiffness, normal equivalent contact stiffness, equivalent loss factor, and friction coefficient is established as the number of loading cycles accumulates. Step 4, after loading, combine surface morphology parameter detection: when the number of loading cycles reaches the preset value, stop the test, remove the bolts of the test sample component (1), clean the connected parts, and then perform a repositioning scan on the same fixed observation window marked in Step 1 to obtain the surface morphology of the final state, including the surface density of the micro-protrusions, the average radius of curvature of the micro-protrusions, the highest peak value of the surface micro-protrusions, the probability density function of the true height of the surface, and the final support rate curve. Step 5, Extraction and Output of True Contact Rate and Evolution Results: Substitute the initial preload recorded in Step 1 into the normal force integral equation of the discretized Greenwood-Williamson model to obtain the elastic equivalent separation distance of the initial state. Substitute the elastic equivalent separation distance of the initial state into the initial support ratio curve obtained in Step 1 for interpolation mapping to obtain the true contact rate of the initial state joint surface. Align the final support ratio curve obtained in Step 4 with the initial support ratio curve in the deep valley region to obtain the equivalent separation distance of the final state. Substitute the equivalent separation distance of the final state into the initial support ratio curve for interpolation mapping to obtain the true contact rate of the final state joint surface. Correlate the true contact rate of the initial state joint surface and the true contact rate of the final state joint surface with the evolution process function established in Step 3, which accumulates with the number of loading cycles, including residual preload, tangential equivalent contact stiffness, normal equivalent contact stiffness, equivalent loss factor, and friction coefficient, to obtain the characterization results of the multi-parameter evolution process of the bolted joint surface.

2. The method for characterizing the multi-parameter evolution process of bolted joint surfaces according to claim 1, characterized in that, The specific implementation process of step three is as follows: No. N Residual preload corresponding to each loading cycle Defined as cycle period T Internal instantaneous preload Time average: In the formula, t is the sampling time of the instantaneous preload; No. N Tangential equivalent contact stiffness corresponding to each loading cycle Secant stiffness characterization is based on the extreme points of the tangential load-displacement hysteresis loop: No. N Normal equivalent contact stiffness corresponding to each loading cycle Secant stiffness characterization is based on the extreme points of the normal load-displacement hysteresis loop: In the formula, and The first N The maximum and minimum values ​​of the tangential load within each loading cycle. and The first N The maximum and minimum values ​​of the tangential relative displacement within each loading cycle. and The first N The maximum and minimum values ​​of the normal load within each loading cycle. and The first N The maximum and minimum values ​​of the normal relative displacement within each loading cycle; No. N Equivalent loss factor corresponding to each loading cycle Defined as the energy dissipated during the loading cycle With maximum elastic strain energy The ratio: Among them, dissipated energy Calculation of the area of ​​the tangential load-displacement hysteresis loop formed by the tangential load and the relative tangential displacement: In the formula, Let be the tangential relative displacement of the bolted joint surface, and let be the abscissa of the tangential load-displacement hysteresis loop. The tangential load borne by the bolted joint surface is represented by the ordinate of the tangential load-displacement hysteresis loop. Among them, the maximum elastic strain energy The area is obtained by using the right triangle formed by the amplitude of the tangential load and the amplitude of the tangential displacement: No. N Friction coefficient corresponding to each loading cycle Defined as the frictional force during the global slip phase within this loading cycle. With residual preload The ratio: The global slip phase is the slip phase corresponding to the tangential load-displacement hysteresis loop entering the force plateau segment; the tangential relative displacement of the bolted joint surface is taken. At that time, the ordinate of the tangential load-displacement hysteresis loop corresponds to and The mean of absolute values ​​is used as friction force , .

3. The method for characterizing the multi-parameter evolution process of bolted joint surfaces according to claim 1, characterized in that, The specific implementation process of step five is as follows: The integral equation for the normal force is: In the formula, This is the initial preload. The initial elastic equivalent separation distance. , and These are the surface density of the micro-protrusions, the average radius of curvature of the micro-protrusions, and the highest peak value of the surface micro-protrusions extracted in step one, respectively. The total area of ​​the mating surfaces. The probability density function of the true surface height extracted in step one. It is the equivalent elastic modulus and satisfies the following conditions: in, and These are the Young's moduli of the two connecting parts that constitute the test specimen assembly (1), respectively. and These are the Poisson's ratios of the materials of the two connectors, respectively. The elastic equivalent separation distance of the initial state Substituting the values ​​into the initial support ratio curve and performing interpolation mapping, we obtain the true contact ratio of the initial state interface. ; Equivalent separation distance of the final state The final support rate curve is obtained by aligning the troughs of the initial support rate curve with the troughs of the troughs. mr >80% of the deep valley tail area is overlapped and aligned, and its vertical absolute translation amount The amount of physical damage to the surface, and the equivalent separation distance in the final state. The equivalent separation distance of the final state Substitute the values ​​back into the initial support ratio curve for interpolation mapping to obtain the true contact ratio of the final state interface. .

4. A multi-parameter evolution process characterization system for bolted joint surfaces, characterized in that, The multi-parameter evolution process characterization system of the bolted joint surface includes a test sample assembly (1), a preload measurement assembly (2), a cyclic load loading assembly (3), a cyclic load measurement assembly (4), a system fixing base assembly (5), a relative displacement measurement assembly (6), and a sensor tooling assembly (7). The preload measuring component (2) is fixed between the nut and the connected part of the test specimen component (1). The test specimen component (1) is clamped on the cyclic load loading component (3) by a hydraulic chuck. The cyclic load measuring component (4) is fixed on the cyclic load loading component (3) by bolts. The two are connected in series and fixed on the system fixed base component (5). The relative displacement measuring component (6) is fixed on the sensor tooling component (7) by bolts. The sensor tooling component (7) is fixed on the system fixed base component (5) by bolts.

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