Third Paper: Traction in Elastohydrodynamic Contacts

Measurements of frictional traction in a circular elastohydrodynamic contact have been made over a comprehensive range of conditions. The results suggest the existence of a limiting shear strength in the fluid film and this is shown to be a function of temperature and contact size. Existing theories of fluid behaviour under extreme conditions of stress are considered and some modifications are suggested. The contribution of asperity contact to surface traction is examined.

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Mixed and Fluid Film Lubrication Characteristics of Worn Journal Bearings

Advances in Tribology ◽

10.1155/2012/296464 ◽

2012 ◽

Vol 2012 ◽

pp. 1-7 ◽

Cited By ~ 2

Author(s):

Toshiharu Kazama ◽

Yukihito Narita

Keyword(s):

Frictional Coefficient ◽

Journal Bearings ◽

Mixed Lubrication ◽

Operating Conditions ◽

Fluid Film ◽

Asperity Contact ◽

Lubrication Regimes ◽

Lubrication Characteristics ◽

Film Lubrication ◽

Fluid Film Lubrication

The mixed and fluid film lubrication characteristics of plain journal bearings with shape changed by wear are numerically examined. A mixed lubrication model that employs both of the asperity-contact mechanism proposed by Greenwood and Williamson and the average flow model proposed by Patir and Cheng includes the effects of adsorbed film and elastic deformation is applied. Considering roughness interaction, the effects of the dent depth and operating conditions on the loci of the journal center, the asperity-contact and hydrodynamic fluid pressures, friction, and leakage are discussed. The following conclusions are drawn. In the mixed lubrication regime, the dent of the bearing noticeably influences the contact and fluid pressures. For smaller dents, the contact pressure and frictional coefficient reduce. In mixed and fluid film lubrication regimes, the pressure and coefficient increase for larger dents. Furthermore, as the dent increases and the Sommerfeld number decreases, the flow rate continuously increases.

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Prediction of the Shear Failure of Opened Rock Fractures and Implications for Rock Slope Stability Evaluation

Advances in Civil Engineering ◽

10.1155/2019/6760756 ◽

2019 ◽

Vol 2019 ◽

pp. 1-7 ◽

Cited By ~ 2

Author(s):

Yingchun Li

Keyword(s):

Shear Strength ◽

Rock Slope ◽

Shear Failure ◽

Rock Slope Stability ◽

Rock Fractures ◽

Asperity Contact ◽

Direct Shear Tests ◽

Proposed Model ◽

The Stability ◽

New Criterion

Rock slope commonly fails due to the shear failure of rock fractures. Shear strength of rock fractures are reduced substantially once the fracture surfaces are mismatched or opened. We propose a new criterion to predict the shear strength of rock fractures in different opening states. The degree of interlocking representing the true asperity contact area is incorporated into the modified model of Saeb and Amadei. The effect of fracture opening on asperity dilation and degradation is separately considered. The transitional stress that is a critical parameter involved in the model is analytically determined based on energy consideration. The new model is validated with experimental results from direct shear tests on synthetic fractures with regular-shaped asperities. Good agreement between the analytical solution and the experimental data confirms the capacity of the proposed model. Therefore, the model has great potential for assessing the stability of rock slopes where fractures are often opened due to stress relief and engineering disturbances.

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Transitions of Shear Resistance in a Single-Asperity Contact

MRS Proceedings ◽

10.1557/proc-539-81 ◽

1998 ◽

Vol 539 ◽

Author(s):

J. A. Hurtado ◽

K.-S. Kim

Keyword(s):

Contact Zone ◽

Shear Force ◽

Friction Stress ◽

Adhesive Contact ◽

Nanometer Scale ◽

Asperity Contact ◽

Normal Loading ◽

Single Asperity ◽

Single Asperity Contact ◽

Contact Size

AbstractThe shear force required to emit circular dislocation loops from the edge of a circular adhesive-contact zone is calculated analytically as a function of contact-zone radii. The emission condition is based on the balance of the configurational force and the Peierls force on a dislocation loop initiated at the edge of the adhesive contact zone. The analysis suggests that there is a transition, for a nanometer-scale single-asperity contact, from concurrent (mobile- dislocation-free) slip to single-dislocation-assisted (SDA) slip. The nanometer-scale friction stress (shear force required for slip/contact area), which experimentally is observed independent of normal loading and contact-zone size, is believed to be the stress required for concurrent slip. The analysis also predicts a second transition from SDA slip to multiple-dislocation-cooperated (MDC) slip at the scale of tens of micrometers in contact size. The friction stress at this large length scale has also been observed experimentally to be independent of normal loading and contact size; however, the friction stress at the nanometer scale is about 30 times that at the scale of tens of micrometers. The analysis is consistent with these experimental observations.

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Non-Hertzian Elastohydrodynamic Contact Stress Calculation of High-Speed Ball Screws

Applied Sciences ◽

10.3390/app112412081 ◽

2021 ◽

Vol 11 (24) ◽

pp. 12081

Author(s):

Tiewei Sun ◽

Min Wang ◽

Xiangsheng Gao ◽

Yingjie Zhao

Keyword(s):

Contact Stress ◽

Calculation Method ◽

High Speed ◽

Contact Region ◽

Friction Torque ◽

Wear Depth ◽

Asperity Contact ◽

Stress Calculation ◽

Elastohydrodynamic Contact ◽

The Asymmetry

In order to eliminate the calculation error of the Hertzian elastohydrodynamic contact stress due to the asymmetry of the contact region of the helix raceway, a non-Hertzian elastohydrodynamic contact stress calculation method based on the minimum excess principle was proposed. Firstly, the normal contact stresses of the screw raceway and the nut raceway were calculated by the Hertzian contact theory and the minimum excess principle, respectively. Subsequently, the Hertzian solution and the non-Hertzian solution of the elastohydrodynamic contact stress could be determined by the Reynolds equation under different helix angles and screw speeds. Finally, the friction torque test of the double-nut ball screws was designed and implemented on a self-designed bed for validation of the proposed method. The comparison showed that the experimental friction torque was the good agreement with the simulated friction torque, which verified the effectiveness and correctness of the non-Hertzian elastohydrodynamic contact stress calculation method. Under the large helix angle, the calculation accuracy of asperity contact stress for the non-Hertzian solution was more accurate than that of the Hertzian solution at the contact region of ball screws. Therefore, the non-Hertzian elastohydrodynamic contact stress considering the asymmetry of the raceway contact region could more accurately analyze the wear depth of the high-speed ball screws.

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Lubricant flow in thin-film elastohydrodynamic contact under extreme conditions

Friction ◽

10.1007/s40544-016-0134-6 ◽

2016 ◽

Vol 4 (4) ◽

pp. 380-390 ◽

Cited By ~ 8

Author(s):

P. Sperka ◽

I. Krupka ◽

M. Hartl

Keyword(s):

Thin Film ◽

Extreme Conditions ◽

Elastohydrodynamic Contact ◽

Lubricant Flow

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Effects of Boundary Films on the Frictional Behavior of Rough-Surface Contacts in Incipient Sliding

World Tribology Congress III, Volume 1 ◽

10.1115/wtc2005-63510 ◽

2005 ◽

Author(s):

L. Chang ◽

H. Zhang ◽

J. Lococo

Keyword(s):

Shear Strength ◽

Rough Surface ◽

Interfacial Shear Strength ◽

Interfacial Shear ◽

Material Research ◽

Asperity Contact ◽

Frictional Behavior ◽

Surface Plasticity ◽

Boundary Film ◽

Boundary Films

Research has shown that the interfacial shear strength in an asperity contact is generally a linear function of the asperity pressure with a maximum value below the shear strength of the substrate material. Research further suggests that the properties of the surface-film materials in the micro-contact largely govern the shear-strength-pressure relation and the maximum attainable interfacial shear strength. This paper studies the effect of boundary films on the frictional behavior of rough-surface contacts in incipient sliding. Two parameters are used to describe the shearing properties of the boundary film. One is the shear-strength-pressure proportionality constant and the other, the ratio of the maximum interfacial shear strength to the substrate shear strength. The study uses an asperity-based mathematical model for frictional sliding-contact of nominally flat elastic-plastic rough surfaces incorporating the above interfacial shearing properties in the asperity contacts. A sequence of parametric studies is carried out to study the frictional behavior of the contact system. The parameters include surface plasticity index, contact load, and boundary film properties. More details of the results along with literature studies and references are presented in a full paper [1].

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Transition from elastic to plastic deformation as asperity contact size is increased

Tribology Letters ◽

10.1007/s11249-007-9199-8 ◽

2007 ◽

Vol 26 (3) ◽

pp. 235-238 ◽

Cited By ~ 4

Author(s):

C. W. Yong ◽

W. Smith ◽

A. Dhir ◽

K. Kendall

Keyword(s):

Plastic Deformation ◽

Asperity Contact ◽

Contact Size

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Holding Power of Orthopaedic Screws in Metacarpal and Metatarsal Bones of Young Calves

Veterinary and Comparative Orthopaedics and Traumatology ◽

10.1055/s-0038-1633077 ◽

1992 ◽

Vol 05 (03) ◽

pp. 100-103 ◽

Cited By ~ 4

Author(s):

G. Jean ◽

J. K. Roush ◽

R. M. DeBowes ◽

E. M. Gaughan ◽

J. Kirpensteijn

Keyword(s):

Shear Strength ◽

Tensile Load ◽

Young Female ◽

Limiting Factor ◽

Holding Power ◽

Metatarsal Bones ◽

Bone Width ◽

Load To Failure ◽

Holstein Calves

SummaryThe holding power and holding power per mm bone width of 4.5 mm and 5.5 mm cortical and 6.5 mm cancellous orthopaedic screws were obtained by tensile load-to-failure studies in excised metacarpal and metatarsal bones of young female Holstein calves. Holding power and holding power per mm bone width of 6.5 mm orthopaedic screws were significantly greater than those of 4.5 and 5.5 mm orthopaedic screws in the diaphysis and metaphysis. Significant differences were not detected between holding power and holding power per mm bone width of 4.5 and 5.5 mm orthopaedic screws. The holding power was not different between metacarpi and metatarsi. The limiting factor in all tests of holding power was the shear strength of the bone. We found that 6.5 mm orthopaedic screws have the greatest holding power in the metacarpal and metatarsal bones of young calves.This study compares the holding power of 4.5 mm and 5.5 mm cortical and 6.5 mm cancellous orthopaedic screws in excised metacarpal and metatarsal bones from young female Holstein calves. We found that 6.5 mm orthopaedic screws have the greatest holding power.

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