The influence of geometrical parameters of the short grooves on the hydrodynamic lubrication is studied in this article. Based on Reynolds equation and Jakobsson-Floberg-Olsson cavitation theory, an analytical model is developed to investigate the hydrodynamic lubrication of the short grooves. The study employs a multigrid method to calculate the distribution of hydrodynamic pressure and the average pressure of textured surfaces. The results indicate that the interactions between neighboring short micro-grooves and the end effect on the hydrodynamic pressure should be considered in the process of numerical simulation. There exist the optimum values of horizontal spacing and short microgroove depth to maximize the hydrodynamic pressure. The average film pressure decreases with the increase in the vertical spacing, but it increases alongside the short groove width. The increase rate of the average pressure declines gradually as the short groove length grows. Therefore, hydrodynamic lubrication performance can be improved by optimizing the geometrical parameters of the short grooves according to operating conditions.

Purpose The purpose of this paper is to find the influence of surface bump texture combination characteristics on friction-wear properties so as to provide a basis for the selection of the bump texture combination scheme on the surface of the roll. Design/methodology/approach In this paper, six groups of different bump texture combination characteristics and their processing methods are introduced, of which three groups are regular distribution with different spacing and three groups are random distribution with different spacing. Then the effect of bump textures with different spacing, regular and random distribution on friction-wear properties was studied by ring block friction-wear experiments. Findings The results show that the friction coefficient of random distribution texture surface is lower than that of regular texture surface under the same spacing condition. In the regular distribution, the friction coefficient decreases with the increase of texture spacing. In the random distribution, the friction coefficient increases at first and then decreases with the increase of texture spacing. In addition, the wear resistance of textured surface is significantly higher than that of smooth surface because of the higher microhardness of the textured area. The attenuation ratio of textured surface roughness decreases with the increase of the distance between adjacent textures. Originality/value At present, the research on roller surface friction-wear is mainly based on the change of the overall surface roughness. However, there are few reports on the influence of the combination characteristics of laser bump texture on friction-wear from the microscopic scale.

Conform and non-conformal contact problem in the face of piezoelectric motors can be hard to grasp, especially both the friction drive and wear lifespan are considered. Flowing the classical contact issue, an elastic brittle flat punch as the driving tip of the stator for piezoelectric devices is chosen and the contact behaviour under elliptical ultrasonic vibration is investigated using finite element method. A limited stress analysis is conducted after the quasi-static contact of the driving tip and the slider of the linear ultrasonic motors. After the analytical traces and experimental test on the fracture failure induced by the stress actions, the failure criteria of the elastic brittle driving tip are discussed. Results show that this quasistatic method can be applied to the complex contact analysis of an elliptical vibration device, and the failure characteristics induced by stress and strain can be obtained by FEM simulation and experiment verification. The pre-fracture stress map provides an important basis for the design of the geometrical mutation edge (e.g. edge fillet) of the elastic brittle punch and the composite structure for strength capacity. The failure analysis of brittle materials under ultrasonic vibration requires attention on quasi-brittle and quasi-plastic strength criterions. This study focus on determination of the contact stresses and the limited states during the elliptical vibration of a stator tip against slider. It also is important for the analysis on failure modes of frictional materials of ultrasonic devices, fretting wear of high-frequency connecting parts and machining process assisted with ultrasonic vibration.

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