The geometry and properties of the friction pair surface.When there is a thin lubricating oil film between the related working surfaces, the approach of the working surfaces will make the peaks and valleys of the two surfaces inhibit or dredge the flow of lubricating oil, which will affect the calculation results of friction and oil film thickness.If the two surfaces are close to each other again, the peaks on both sides will contact or collide. The friction heat generated from this will not only have a thermal effect on the oil, but also affect the formation and fracture of the boundary film.As for the running in and wear process of the contact friction pair surface, of course, it is more related to the original surface morphology and wear scar morphology.Surface morphology is very important for the study of tribology, but it was not until the 1960s that people gradually realized it, and it was not until the late 1970s that it was associated with the study of surface damage.
The real surface belongs to the three-dimensional geometric form, which can be described as the working surface in the rectangular coordinate system (Figure 1 [3D surface topography]), and is the surface heightAxis。The average height line (centerline) of the surface profile of a section is the coordinate axis (Figure 2 [Surface profile of the section]). There are many ways to express the average height, such as the arithmetic mean value [0027-05] and the root mean square value [0027-06] of the profile, where L is the sampling length.They are one-dimensional parameters representing the direction and size.The distance and frequency characterizing the contour fluctuation are one-dimensional parameters of direction size, such as the mean intercept S m between adjacent intersections of the contour curve on the centerline or the mean density of the intersection of the centerline [0027-01].To characterize the two-dimensional shape of the profile, the parameters in and directions are needed.However, more parameters are needed to describe the difference of contour changes.If the surface morphology distribution is normal, if the selection is reasonable, only three one-dimensional parameter groups are enough to express it.P. R. Nayak recommended three parameters [6], [0027-01] and [0027-02] according to the random theory.Wherein, [0027-01] is the average number of times that the contour curve crosses the centerline per unit length (i.e. the density of intersection points of the centerline);[0027-02] is the mean value of the number of peaks per unit length (i.e. peak density).
For tribological problems, it is necessary to understand not only the variation law of contour height, but also the degree of asymmetry of contour distribution to the centerline, the average slope of each point of the contour, the average peak curvature and the average peak height.
Comprehensive effect
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preface
For tribological problems, the combined effects of the two surfaces that make up the friction pair must be considered.For the contact and friction and wear problems of real surfaces (considering the roughness effect), not only the dry friction working conditions should be studied, but also the working conditions with lubricants or various surface films between interfaces should be considered.
Situation 1
① Film thickness ratio [a1]=/[6], a dimensionless parameter commonly used to characterize the thickness of oil film.Where is the oil film thickness;[0027-07] is a friction pair with comprehensive roughness and lubricating film. [a1]>3 belongs to the state of full elastohydrodynamic lubrication. The oil film bears most of the load, and will not stick [a1]<1 belongs to the boundary lubrication state, which is easy to stick. Even if the heat is not large, adhesion 1 ≤ [a1] ≤ 3 may occur, which belongs to the state of partial elastohydrodynamic lubrication. Surface fluctuation will affect the flow of lubricating oil,Adhesion may occur.
Situation II
② Contact surface peak collision, such as plastic deformation, may lead to adhesion.The plasticity index [4] can be used as a basis to judge whether deformation enters plasticity.If the physical model of the peak is spherical, it can be derived according to the elastoplastic theory
[0028-01] Formula E is the comprehensive elastic modulus of the peak material
[0028-02] Where E1 and E 2 are the elastic modulus of the materials that make up the two parts of the friction pair, 1 and 2 are their Poisson's ratios, H is the Brinell hard bottom of the peak material, [6] is the average peak height (the mean square root of the average peak position height), and is the radius of curvature of the average peak.
