Quantitative characterization method for friction pair surface matching

Abstract

The invention discloses a quantitative characterization method for surface matching of a friction pair, which comprises the following steps: carrying out a friction test on a friction pair to be tested, and carrying out surface profile data acquisition on the friction pair; according to the surface contour data of the two surfaces of the friction pair, the fractal dimensions of the grinding crack contour curves of the two surfaces of the friction pair are calculated; and determining the matching degree of the two surfaces of the friction pair according to the fractal dimensions of the grinding crack profile curves of the two surfaces of the friction pair. According to the method, the evolution law of the surface features in the friction process is analyzed through fractal dimensions, and the matching similarity degree of the two friction surface contours is judged. According to the quantitative characterization method for the surface matching of the friction pair, the fractal dimension of the dual friction surface can be more accurately obtained, and the matching similarity degree of the profiles of the two friction surfaces is quantified and standardized through the fractal dimension. The method is wide in application range, can be widely applied to friction pair matching research in the tribology field, and facilitates optimization of materials and surface treatment processes of friction pairs in design and manufacturing stages.

Description

Technical Field

[0001] The invention relates to the technical field of tribology, in particular to a quantitative characterization method for the matching of friction pair surfaces. Background Art

[0002] In mechanical systems, the surface state of friction pairs plays a vital role in the performance and reliability of the system. The surface morphology, surface roughness and other characteristics of friction pairs directly affect the friction coefficient, wear rate and lubrication state of the contact surface. Traditional surface state characterization methods, such as optical microscopy, white light interferometry or atomic force microscopy, can provide intuitive images of surface morphology or quantitative data of roughness, but they have certain limitations. Specifically, when characterizing surface features, traditional measurement methods often rely on the selected measurement scale, but the surface morphology will show different characteristics at different scales. Therefore, when using lenses with different magnifications or measuring at different resolutions, the measurement results will be different. This scale dependence leads to errors in the measurement results, especially in situations where accurate characterization of surface matching is required. This error may have a significant impact on the design and performance evaluation of mechanical systems. In addition, traditional surface roughness parameters, such as Ra, Rz, etc., can only provide limited surface feature information and cannot fully reflect the complexity and dynamic changes of surface morphology, especially the surface evolution law of friction pairs during the running-in process and the matching characteristics of the dual surfaces. Summary of the invention

[0003] In view of the problem in the prior art that the surface characterization parameters are related to the scale and the morphological characteristics of the friction pair surface at different scales cannot be accurately characterized, the present invention provides a quantitative characterization method for the matching of the friction pair surfaces. The purpose is to achieve quantitative characterization of the surface morphology and the matching of the dual pair surfaces by solving the fractal dimension of the friction pair surfaces, and then to achieve accurate evaluation of the friction pair surface state, thereby improving the design accuracy and operation reliability of the mechanical system.

[0004] In a first aspect, a method for quantitatively characterizing the matching of friction pair surfaces is provided, comprising:

[0005] Conduct friction test on the friction pair to be tested and collect surface profile data of the friction pair;

[0006] According to the surface profile data of the two surfaces of the friction pair, the fractal dimension of the wear scar profile curves of the two surfaces of the friction pair is calculated;

[0007] The matching degree of the two surfaces of the friction pair is determined according to the fractal dimension of the wear scar profile curves on the two surfaces of the friction pair.

[0008] In combination with the first aspect, in certain implementations of the first aspect, the fractal dimension of the wear scar profile curve is determined by the slope k of a double logarithmic relationship curve between a structure function S(τ) of the surface profile of the worn area and τ.

[0009] In conjunction with the first aspect, in some implementations of the first aspect, the following conditions are met: D is the fractal dimension of the wear scar profile curve, and τ is the arbitrarily selected coordinate displacement increment.

[0010] In combination with the first aspect, in certain implementations of the first aspect, the double logarithmic relationship curve between the function S(τ) and τ satisfies: lgS(τ)=lgC+α(D)lgτ, C is the scale coefficient, and α(D) is a function of the fractal dimension D of the wear scar profile curve.

[0011] In combination with the first aspect, in some implementations of the first aspect, α(D)=4-2D.

[0012] In combination with the first aspect, in some implementations of the first aspect, S(τ)=<[t(x+τ)-t(x)] 2 >=Cτ 4-2D , t(x) is the contour curve of the fractal surface, [t(x+τ)-t(x)] 2 is the arithmetic mean of the square of the difference, and <> is the spatial average.

[0013] In combination with the first aspect, in certain implementations of the first aspect, when the difference in fractal dimensions of wear scar profile curves of the two surfaces is less than a preset threshold, the matching degree of the two surfaces of the friction pair meets the requirement.

[0014] In combination with the first aspect, in certain implementations of the first aspect, for a steel-steel friction pair, when the difference in fractal dimensions of wear scar profile curves on the two surfaces is less than 0.1, the matching degree of the two surfaces of the friction pair meets the requirements.

[0015] In combination with the first aspect, in certain implementations of the first aspect, for a plastic-metal friction pair, when the difference in fractal dimensions of wear scar profile curves on the two surfaces is less than 0.2, the matching degree of the two surfaces of the friction pair meets the requirement.

[0016] In combination with the first aspect, in certain implementations of the first aspect, surface profile data of the friction pair is collected by a three-dimensional white light interferometer.

[0017] Compared with the prior art, the solution provided by the present invention includes at least the following beneficial technical effects:

[0018] (1) Based on the fractal theory of friction system, the fractal dimension of the friction pair surface profile curve can be accurately and intuitively obtained through theoretical formula calculation. The fractal parameters that are independent of size are used to quantitatively characterize the matching similarity of the friction surfaces, overcoming the problem of size correlation in the measurement results of traditional measurement methods and improving the accuracy of the matching evaluation of the friction pair surfaces.

[0019] (2) The quantitative characterization method of the friction pair surface matching can quantitatively characterize the running-in state and surface matching of the friction pair surface. It can also be used as one of the criteria for judging the running-in state of the friction pair surface. It can effectively monitor the changes in the surface state of the friction pair during the running-in process, which helps to predict the wear trend and optimize the running-in process.

[0020] (3) The method for quantitatively characterizing the surface matching of a friction pair of the present invention is feasible and highly practical. It can not only quantitatively characterize the running-in state and surface matching of the friction pair surface, but also is easy to operate and can be easily promoted and applied in engineering practice. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The wear scar morphology and cross-sectional profile curve of the dual friction pair after the friction experiment of the present invention. Among them, (a) the wear scar morphology of the upper sample, (b) the cross-sectional profile curve of the wear scar of the upper sample, (b) the wear scar morphology of the lower sample, and (d) the cross-sectional profile curve of the wear scar of the lower sample.

[0022] Figure 2 It is the double logarithmic relationship curve between the structure function S(τ) and τ of the surface profile of the wear area of ​​the present invention. Among them, (a) the double logarithmic relationship curve between the structure function S(τ) and τ of the upper and lower test surface profiles, and (b) the four positions selected for the lower test surface profile. DETAILED DESCRIPTION

[0023] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] The present invention provides a method for quantitatively characterizing the matching performance of friction pair surfaces, and the specific steps are as follows.

[0025] Step (1) is to conduct a friction test on the friction pair to be tested and collect surface profile data of the friction pair.

[0026] The friction pair is usually formed by the friction between the upper and lower samples. After the friction test, a three-dimensional white light interferometer can be used to perform a profile analysis on the wear area on the friction pair surface after the friction test to obtain the wear scar morphology of the upper and lower samples and the wear scar cross-sectional profile curve, such as Figure 1 shown. Figure 1The upper specimen is a steel ball, and the lower specimen is a disc. The friction test is a ball-disc point contact rotation test. After the friction test, the wear marks of the upper specimen steel ball are circular spots, and the wear marks of the lower specimen disc are circular rings. Multiple positions can be selected on the circular wear marks of the lower specimen disc for profile curve collection as needed. During the surface profile data collection process, the stability and repeatability of the equipment during the scanning process should be ensured to obtain accurate surface profile curve data.

[0027] Step (2), obtaining the fractal characteristics of the running-in surface by calculating the fractal dimension of the wear scar profile curve.

[0028] The rough surface is a two-dimensional fractal set, and the contour curve is a one-dimensional fractal set. Usually, the fractal dimension of the surface is D b The fractal dimension D of the contour curve has the following relationship:

[0029] D b =D+1 (1)

[0030] The present invention adopts the structure function method to calculate the fractal dimension, which is applicable to fractal surfaces with affine self-similar characteristics. In the calculation process, the contour curve of the fractal surface can be regarded as a time series t(x), and the formula is

[0031] S(τ)=<[t(x+τ)-t(x)] 2 >=Cτ 4-2D (2)

[0032] Where t(x) is the contour curve of the fractal surface, [t(x+τ)-t(x)] 2 is the arithmetic mean of the square of the difference, <> is the spatial average, C is the scale coefficient, τ is the arbitrarily selected coordinate displacement increment, and D is the fractal dimension of the surface profile curve.

[0033] For the convenience of calculation, the above formula (2) is written as a power law relationship

[0034] S(τ)=Cτ α(D) (3)

[0035] Where α(D) is a function of the fractal dimension D of the surface profile.

[0036] Taking the logarithm of both sides of formula (3) we can get

[0037] lgS(τ)=lgC+α(D)lgτ (4)

[0038] Plotting the above equation in double logarithmic coordinates yields a straight line with a slope of k. The relationship between the surface profile fractal dimension D and the slope k is:

[0039]

[0040] The double logarithmic relationship curve between the structure function S(τ) and τ of the surface profile of the wear area is obtained by using the structure function method, as shown in Figure 2 As shown. Figure 2 It can be seen that the double logarithmic curves under different experimental conditions all have a straight line segment with good linearity. The slope k of the straight line segment of each curve can be obtained by fitting the data of the straight line segment using the least squares method. Substituting the slope k into formula (5), the fractal dimension D of the surface profile curve can be calculated.

[0041] Step (3), friction pair surface matching analysis.

[0042] The fractal dimensions of the two friction pair surfaces are compared and analyzed to evaluate the degree of matching between them. When the fractal dimensions of the two surfaces are consistent, the friction pair has a high degree of matching, indicating that the friction surfaces fit each other like comb teeth, resulting in a larger contact area. Furthermore, in the technical field of matching brushes and conductive slip rings, a larger contact area can further reduce the contact resistance, which is beneficial to the electrical performance of the brushes and conductive slip rings.

[0043] In some embodiments, a threshold value of fractal dimension difference can be set according to actual needs. When the fractal dimension difference between two surfaces is less than the threshold value, it can be considered that the two surfaces have good matching; otherwise, the matching is poor. Regarding the setting of the fractal dimension difference threshold value, it is necessary to comprehensively consider the friction pair material, application scenario, etc. Some commonly used fractal dimension difference threshold values ​​are as follows:

[0044] For steel-steel friction pairs, it is generally believed that when the fractal dimension difference is less than 0.1, the surface matching is good.

[0045] For plastic-metal friction pairs, it is generally believed that when the fractal dimension difference is less than 0.2, the surface matching is good.

[0046] The present invention introduces scale-independent fractal parameters, solves the scale dependence problem of traditional surface characterization parameters, and ensures the stability and comparability of measurement results at different scales. First, a three-dimensional white light interferometer is used to analyze the wear area of ​​the friction pair after the friction test to obtain the wear scar morphology and cross-sectional profile curve of the upper and lower samples; secondly, the structure function method and the least squares method are used to accurately solve the fractal dimension of the surface profile of the friction pair; finally, the surface matching of the dual friction pair is evaluated by comparing the fractal dimensions of the wear scar surface profiles of the upper and lower samples. The present invention analyzes the evolution law of surface features during the friction process by fractal dimension and determines the matching similarity of the profiles of the two friction surfaces. The quantitative characterization method for the surface matching of the friction pair described in the present invention can more accurately obtain the fractal dimension of the dual friction surface, and quantitatively standardize the matching similarity of the profiles of the two friction surfaces by fractal dimension. The method has a wide range of applications and can be widely used in the research on the matching of friction pairs in the field of tribology, which is helpful to optimize the materials and surface treatment processes of the friction pairs in the design and manufacturing stages.

[0047] Although the present invention is disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be based on the scope defined by the claims of the present invention.

Claims

1. A quantitative characterization method for the matching of friction pair surfaces, characterized in that: include: Conduct friction test on the friction pair to be tested and collect surface profile data of the friction pair; According to the surface profile data of the two surfaces of the friction pair, the fractal dimension of the wear scar profile curves of the two surfaces of the friction pair is calculated; The matching degree of the two surfaces of the friction pair is determined according to the fractal dimension of the wear scar profile curves on the two surfaces of the friction pair.

2. The method according to claim 1, characterized in that The fractal dimension of the wear scar profile curve is determined by the slope k of the double logarithmic relationship curve between the structure function S(τ) of the surface profile of the wear area and τ.

3. The method according to claim 2, characterized in that satisfy: D is the fractal dimension of the wear scar profile curve, and τ is the arbitrarily selected coordinate displacement increment.

4. The method according to claim 3, characterized in that: The double logarithmic relationship curve between the function S(τ) and τ satisfies: lgS(τ)=lgC+α(D)lgτ, C is the scale coefficient, and α(D) is a function of the fractal dimension D of the wear scar profile curve.

5. The method according to claim 4, characterized in that α(D)=4-2D.

6. The method according to claim 5, characterized in that S(τ)=<[t(x+τ)-t(x)] 2 >=Cτ 4-2D , t(x) is the contour curve of the fractal surface, [t(x+τ)-t(x)] 2 is the arithmetic mean of the square of the difference, and <> is the spatial average.

7. The method according to claim 1, characterized in that When the difference in fractal dimension of the wear scar profile curves of the two surfaces is less than a preset threshold, the matching degree of the two surfaces of the friction pair meets the requirements.

8. The method according to claim 7, characterized in that For the steel-steel friction pair, when the difference in fractal dimension of the wear scar profile curves on the two surfaces is less than 0.1, the matching degree of the two surfaces of the friction pair meets the requirements.

9. The method according to claim 7, characterized in that: For the plastic-metal friction pair, when the difference in fractal dimension of the wear scar profile curves on the two surfaces is less than 0.2, the matching degree of the two surfaces of the friction pair meets the requirements.

10. The method according to claim 1, characterized in that The surface profile data of the friction pair is collected by three-dimensional white light interferometry.

Images