摘要:

AbstractModels of typical characteristics of the surfaces of two solids interfacing one another under pressure and sliding with respect to each other are described in Models1 (Figure 1)and 2(Figure 2).In Model 1(Figure 1)the asperities, wedges of the harder surface indent into the softer surface due to the applied pressure, thus producing opposing ridges on the surface of the softer component. The gap between the opposing asperities is filled with liquid, establishing boundary lubrication. As sliding is maintained, the ridges are mobilized and an eddy flow is established in the trapped lubricant. The power required to mobilize the ridges and to establish eddy flow in the lubricant is calculated and thus the friction resistance to sliding is determined. Simultaneously, the pressure generated in the liquid due to shear is also evaluated. It becomes clear that the height of the ridge due to indentation is inversely proportional to the speed of sliding. The higher the sliding speed, the higher is the liquid pressure that is countering the loading pressure and the smaller is the indentation. At a high enough speed (to be replaced in due course by the Sommerfeld Number) the entire load is supported by the pressure generated in the liquid, indentation is eliminated and hydrodynamic lubrication commences. The classic model for hydrodynamic lubrication where two inclined surfaces glide atop each other is described in figure 2. Here the gap between the two surfaces (q.J a t their closest point is a monotonically increasing function of Sommerfeld Number (S). The resistance to sliding as established through the shear in the liquid determines thefriction value. This model leads directly to the characteristic of Coulomb or Emontons where for diminishing values of Sommerfeld Number the resistance to sliding is proportional to the pressure (τ = μp) and the proportionality factor is equal to the tangent of the angle of inclination (μ = tana). In the present work, the increase infnction with increasing values of the Sommerfeld Number is also determined. Combining the two models one notices that, a t low speed and Somrfeld Number values, the liquid pressure is not sufftcient tofloat the two surfaces and indentation prevails together with boundary lubrication. With increasing speed (Sommerfeld Number) the height of the ridge (by Model 1) decreases, and when it diminishes to values lower than those predicted for the gap between the surfaces in the second model for the same speed, the boundary lubrication ceases and hydrodynamic lubrication commenc

ISSN:0954-0075    

DOI:10.1002/ls.3010020202

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractMany rolling and sliding contacts in industrial machineries are lubricated elastohydrodynamically to mitigate friction and wear. Predictions of tribological failures and performance have been greatly enhanced in the past two decades due to advancements in elastohydrodynamics. In this paper, the major physical features and principles of elastohydrodynamic lubrication (EHL) along with the major modes of tribological failures are summarized, first, for these contacts. Brief discussions are given to current predictability of lubricant film thickness, contact pressure, temperature, and friction in elastohydrodynamic contacts, and how these variables are used in predicting contact fatigue life and the threshold conditions for sliding failure.

ISSN:0954-0075    

DOI:10.1002/ls.3010020203

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThis paper reviews recent work on oil viscosity, volatility and consumption, and describes the conditions under which oil loss occurs, and the processes involved, in automotive engines, generally under fired conditions. Also examined is the evolution of the SAE J300 viscosity classification system, and its relationship to the work going on currently.

ISSN:0954-0075    

DOI:10.1002/ls.3010020204

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThis paper reports work on stability in suspension of white solid lubricants in a number of media. Lubricants included calcium carbonate, calcium hydroxide, and calcium acetate. Additives were used to increase suspension stability, and centrifugation to obtain sedimentation.

ISSN:0954-0075    

DOI:10.1002/ls.3010020205

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

ISSN:0954-0075    

DOI:10.1002/ls.3010020201

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY