Action mechanisms of boundary lubrication additives — A review,Part I

A wide range of literature has been published in the period 1950–2000 concerning emerging concepts relating to the action mechanisms of boundary lubrication additives. Some of the details of these additives in terms of chemical nature, surface adsorption, surface film generation, thermal stability, thermodynamics of contact surfaces, and rise in surface temperature, as reported in this literature, are reviewed in the present paper. It has been observed that the chemical constituents of boundary lubrication additives, particularly of organosulphur and organosulphur—phosphorus origin, are very complex in nature and no comprehensive details are readily available. Regarding action mechanisms, different researchers have suggested different mechanisms for different conditions. However, information on the thermodynamics of surfaces and thermal stability of additives is not readily available. Other details, such as the effect of sliding speed, operating load, surface roughness, and material design, are not covered in this paper. Overall, the literature reveals that attempts to correlate additive characteristics with boundary lubrication activity have met with limited success, and efforts aimed at achieving ever‐increasing performance levels are continuing. In this first part, the authors examine the chemical nature of boundary lubrication additives, the surface films produced, and surface temperature.     

Action mechanisms of boundary lubrication additives ‐ a review,part II

A wide range of literature hs been published in the period 1950–2000 concerning emerging concepts of the action mechanisms of boundary lubrication additives. Some aspects of these additives in terms of chemical nature, surface adsorption, surface film generation, thermal stability, thermodynamics of contact surfaces, and rise in surface temperature, as reported in this literature, are reviewed in the present paper.

1 Part I of this paper appeared in Lubrication Science, 16, 4 (2004) 405–19.

It has been observed that the chemical constituents of boundary lubrication additives, particularly of organosulphur and organo‐sulphur‐phosphorus origin, are very complex in nature and no comprehensive details are readily available. Regarding action mechanisms, researchers have suggested different mechanisms for different conditions. However, information on the thermodynamics of surfaces and thermal stability of additives is not easily obtainable. Other details, such as the effect of sliding speed, operating load, surface roughness, and material design, are not covered here. Overall, the literature reveals that attempts to correlate additive characteristics with boundary lubrication activity have met with limited success, and efforts aimed at achieving ever‐increasing performance levels continue. In the first part, the authors examined the chemical nature of boundary lubrication additives, surface films, and surface temperature. In this second part, they look at thermal stability, and antiwear and extreme‐pressure activity.     

A test method to study the change in surface topography due to running‐in of a rolling contact

A method is proposed to determine the change in surface topography during running‐in of rolling contacts. Two types of experiments have been conducted in the present work to study the running‐in of the pure rolling contact situation: repeated moving and general free rolling using a high accuracy measurement setup. The results show that the surfaces run‐in with the proposed repeated moving contact method gives a fast running‐in when compared with the general free rolling contact method. The proposed repeated moving contact method appears to be a good method to study the ideal or pure rolling contact situation because wear, as present in the general free rolling contact method, is avoided. Copyright © 2013 John Wiley & Sons, Ltd.     

A new methodology for determining the stress state of the plastic region in machining with restricted contact tools

In rigid-plastic slip-line theory, once the geometry of the slip-line field is established, the stress state of the plastic region (including the primary and secondary deformation zones) in restricted contact machining is governed by the hydrostatic pressure P_A (at a point on the intersection line of the shear plane and the work surface to be machined) and the frictional shear stress τ on the tool rake face. Based on the recently established universal slip-line model and a detailed study of six representative machining cases, a new methodology for determining the stress state of the plastic region, i.e. maximum value principle, is presented in this paper. According to this principle, the stress state of the plastic region can be determined by giving both P_A and τ their theoretical maximum permissible values. The theoretical maximum permissible values of P_A and τ can be found by satisfying four mechanical and geometrical constraint conditions under which the universal slip-line model applies. A comprehensive assessment factor is introduced in this paper. It is shown that the three machining parameters investigated in this present study, i.e. cutting force ratio, chip thickness ratio, and chip back-flow angle can be simultaneously considered to form a comprehensive criterion to compare predicted and experimental results. The applicable range of the maximum value principle is also discussed.     

Dynamic plastic behavior of a free–free beam striking the mid-span of a clamped beam with shear and membrane effects considered

Recently Yu et al. (Int. J. Solids Struct. 38 (2001) 261) made a study on the dynamic behavior of a flying free–free beam striking the tip of a cantilever beam using the rigid, perfectly plastic (r-p-p) material model. Later, also based on the r-p-p material model Yang and Yu (Mech. Struct. Mach. 29 (2001) 391) analyzed another impact problem of a free rotating hinge beam striking a cantilever beam. Both of these studies ignored the finite deflection effects on the plastic behavior of the colliding beams. However if the free–free beam strikes a clamped beam, the influence of finite-deflections, or, geometric changes, must be retained in the governing equation if the maximum permanent transverse displacement of the clamped beam exceeds the corresponding beam thickness. The problem becomes more interesting since the deformation mechanisms of the beam system and the partitioning of energy dissipation in the beams are significantly different from those predicted by ignoring the influence of membrane forces. Accordingly the failure modes of the structure are different.In the present paper, a theoretical model based on the r-p-p material idealization is proposed to simulate the dynamic behavior when the mid-point of a translating free–free beam impinging on the mid-span of a clamped beam with the beam axes perpendicular to each other. The plastic behavior of the beam system is explored with shear sliding and finite deflection effects taken into account. The final deflection, the dissipation of energy within the two beams after impact and the influence of the structural and material parameters are discussed. It is shown that membrane force plays an important role during the response process, especially when the deflection is of the same order as the thickness of the clamped beam.     

少齿差行星减速器孔销式输出机构的强度和刚度初探

少齿差行星减速器的孔销式输出机构是制约减速器承载能力主要的环节之一,主要是销轴、销孔间接触强度、刚度及销轴的弯曲强度、刚度所致。而它的力学计算属于超静定问题。这里分别采用材料力学的方法和弹性力学有限元方法及分析软件COSMOSDesignSTAR分析销轴及与其相关零件的强度和刚度的结果,目的是找出提高减速器承载能力的途径。