Comparative Evaluation of MoS2 and WS2 as Powder Lubricants in High Speed, Multi-Pad Journal Bearings

Higgs, C. Fred; Heshmat, Crystal A.; Heshmat, Hooshang

doi:10.1115/1.2834113

Cited by 47 publications

(15 citation statements)

References 5 publications

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“…Though poorly understood, possible weakening mechanisms for the decrease in the friction coefficient above 0.70 m/s are powder lubrication and thermochemical pressurization. Powder lubrication is a not well understood dynamic weakening mechanisms claimed to be active in ultra‐fine gouges [ Han et al , 2010; Reches and Lockner , 2010] and engineering materials (MoS 2 , WS 2 [ Higgs et al , 1999; Wornyoh et al , 2007]). Thermochemical pressurization is the result of thermal expansion of fluids released, during frictional sliding, by breakdown or decomposition reactions of H 2 O or CO 2 bearing minerals [ Brantut et al , 2010].…”

Section: Discussionmentioning

confidence: 99%

Low- to high-velocity frictional properties of the clay-rich gouges from the slipping zone of the 1963 Vaiont slide, northern Italy

et al. 2011

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[1] The final slip of about 450 m at about 30 m/s of the 1963 Vaiont landslide (Italy) was preceded by >3 year long creeping phase which was localized in centimeter-thick clay-rich layers (60-70% smectites, 20-30% calcite and quartz). Here we investigate the frictional properties of the clay-rich layers under similar deformation conditions as during the landslide: 1-5 MPa normal stress, 2 × 10 −7 to 1.31 m/s slip rate and displacements up to 34 m. Experiments were performed at room humidity and wet conditions with biaxial, torsion and rotary shear apparatus. The clay-rich gouge was velocity-independent to velocity-weakening in both room humidity and wet conditions. In room humidity experiments, the coefficient of friction decreased from 0.47 at v < 5.0 × 10 −5 m/s to 0.12 at 1.31 m/s. Microstructural and mineralogical analyses of the gouge after experiments indicate that the dramatic weakening results from thermo-chemical pressurization of pore fluids (smectite decomposition to illite-type clays) and powder lubrication. In wet experiments, the coefficient of friction decreased from 0.17 at v < 1.0 × 10 −4 m/s to 0.0 at v > 0.70 m/s: full lubrication results from the formation of a continuous water film in the gouge. The Vaiont landslide occurred under wet to saturated conditions. The unstable behavior of the landslide is explained by the velocity-weakening behavior of the Vaiont clay-rich gouges. The formation of a continuous film of liquid water in the slipping zone reduced the coefficient of friction to almost zero, even without invoking the activation of thermal pressurization. This explains the extraordinary high velocity achieved by the slide during the final collapse.

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Section: Discussionmentioning

confidence: 99%

Low- to high-velocity frictional properties of the clay-rich gouges from the slipping zone of the 1963 Vaiont slide, northern Italy

et al. 2011

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“…Over the course of past 20 years, dry particulate lubrication has been attempted in many industrial fields, such as the bearing [6][7][8], engine [9], milling [10,11], casting [12], and so on, which was proven to be an effective and promising lubrication method.…”

Section: Introductionmentioning

confidence: 99%

Effects of Sliding Velocity and Normal Load on Tribological Characteristics in Powder Lubrication

et al. 2011

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The antifriction ability of powder lubrication and the state of powder layer are strongly related to the service conditions. Therefore, the effects of sliding velocity and normal load under powder lubrication were studied using a face-to-face contact tribometer. In our work, some graphite, a widely used solid lubricant, was introduced into the frictional interface in the state of free powder. Varying friction coefficient and temperature rise were recorded online. The powder layer formed on the frictional surface of the bottom samples was observed by an optical microscope after tests. The comparative research demonstrated the tribological characteristics of powder lubrication are similar to that of polytetrafluoroethylene coating. Besides, the powder lubrication provides longer lubrication life, although the powder was difficult to seal and control during the tests. Within the proper range of sliding velocities and normal loads, the powder layer dynamically formed on the contact surface of the bottom samples, which resulted in the self-replenishing and oil-free lubrication. The powder layer inclined to deteriorate under lower velocity and higher load. The tests with higher velocity exhibited lower friction coefficient and higher temperature rise. The tests with lower load exhibited higher friction coefficient and lower temperature rise. The state of powder layer included typically four stages such as the full layer, the partial detachment, the serious detachment, and the complete destruction. The damage degree of powder layer is not in proportion to the friction coefficient or the temperature rise due to the particularity of powder lubrication.

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“…Researchers have proposed innovative forms of particulate lubrication that can lower the friction and prevent the wear in sliding contact interfaces [2,[9][10][11]. Navier-Stokes equations themselves can only be solved for the simplest cases, and when they are modified for use with granular flows, they become increasingly more complex.…”

Section: Introductionmentioning

confidence: 99%

An evaluation of the explicit finite-element method approach for modelling dense flows of discrete grains in a Couette shear cell

Kabir

Jasti

Higgs

et al. 2008

Proceedings of the Institution of Mechanical Engineers, Part J:

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Granular flows are complex materials that are composed of discrete solid particles that can display gaseous, liquid, and/or solid behaviour under various conditions. Consequently, tribologists have studied them for their ability to carry loads and/or accommodate sliding surface velocities. Because of the highly non-linear behaviour of granular materials, their behaviour is difficult to predict. One new modelling approach that holds promise in simulating the behaviour of these particulate materials is the explicit finite-element method (FEM). The explicit FEM is a computational modelling approach capable of capturing dynamic, transient events, such as collisions and particle-particle interactions of grains in granular flows. This paper presents an explicit FEM simulation of a dense flow of steel particles in a rough gravity-free Couette shear cell with no externally applied load. Parametric tests of this cell are also carried out by varying the height of the shear cell and the types of known granular materials sheared in the cell. Subsequently, a final evaluation of the explicit FEM approach is conducted by simulating a dense flow of sheared titanium oxide (TiO 2 ) powder in the shear cell and comparing it to a similar simulation done using the discrete-element method (DEM) approach. In this comparison, the velocity of the flow in the DEM cell is larger, whereas the FEM and DEM solid fraction distributions are almost identical in the core regions of the shear cells. The merits of the FEM and DEM approaches are presented in light of the results shown in this work.

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Comparative Evaluation of MoS2 and WS2 as Powder Lubricants in High Speed, Multi-Pad Journal Bearings

Cited by 47 publications

References 5 publications

Low- to high-velocity frictional properties of the clay-rich gouges from the slipping zone of the 1963 Vaiont slide, northern Italy

Low- to high-velocity frictional properties of the clay-rich gouges from the slipping zone of the 1963 Vaiont slide, northern Italy

Effects of Sliding Velocity and Normal Load on Tribological Characteristics in Powder Lubrication

An evaluation of the explicit finite-element method approach for modelling dense flows of discrete grains in a Couette shear cell

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