Relationship of hertzian contact pressure to friction behavior of self-lubricating boric acid films

1991 ◽  
pp. 435-438
Author(s):  
Ali Erdemir ◽  
Robert A. Erck ◽  
Jorge Robles
Keyword(s):  
Boric Acid ◽  
Contact Pressure ◽  
Hertzian Contact ◽  
Friction Behavior ◽  
Relationship Of

scholarly journals Stress- and Time-Dependent Formation of Self-Lubricating In Situ Carbon (SLIC) Films on Catalytically-Active Noble Alloys

JOM ◽  
2021 ◽  
Author(s):  
Morgan R. Jones ◽  
Frank W. DelRio ◽  
Thomas E. Beechem ◽  
Anthony E. McDonald ◽  
Tomas F. Babuska ◽  
...  
Keyword(s):  
Shear Strength ◽  
Steady State ◽  
Contact Pressure ◽  
Film Formation ◽  
Systematic Investigation ◽  
Time Dependent ◽  
Hertzian Contact ◽  
Friction Behavior ◽  
Catalytically Active

AbstractLow shear strength (30 MPa) organic films were grown in situ on Pt0.9Au0.1 surfaces via cyclic sliding contact in dry N2 with trace concentrations of ambient hydrocarbons. We present a systematic investigation of the stress- and time-dependent film formation. Steady-state friction coefficients were found to be as low as µ ~ 0.015 and inversely proportional to contact pressure, revealing non-Amontonian behavior. Above a Hertzian contact pressure of ~500 MPa, shear strength dropped, indicating an activated process. Raman spectroscopy identified non-uniformity in areal coverage and relative order with contact pressure. Regions of steady-state low-friction behavior exhibited spectra similar to DLC coatings. Atomic force microscopy was used to study the formation and growth of films at the nanoscale. Stress- and time-dependent measurements suggested a sublinear increase of film volume with time, and a transition from growth to wear at a Hertzian contact pressure of ~1.2 GPa.

Approximate Analytical Model for Hertzian Elliptical Wheel/Rail or Wheel/Crossing Contact Problems

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
F. D. Fischer ◽  
M. Wiest
Keyword(s):  
Contact Pressure ◽  
Contact Problems ◽  
Hertzian Contact ◽  
Contact Theory ◽  
Technical Accuracy ◽  
Elliptical Contact ◽  
Current Approximation ◽  
Analytical Expressions ◽  
Maximum Contact ◽  
Hertzian Contact Theory

The Hertzian contact theory is approximated according to a concept by Tanaka (2001, “A New Calculation Method of Hertz Elliptical Contact Pressure,” ASME J. Tribol., 123, pp. 887–889) yielding simple analytical expressions for the elliptical semi-axes, the maximum contact pressure, the mutual approach and the contact spring constant. Several configurations are compared using the exact Hertz theory and the current approximation. The results agree within technical accuracy.

Tongue–Palate Contact Pressure, Oral Air Pressure, and Acoustics of Clear Speech

2013 ◽  
Vol 56 (3) ◽  
pp. 826-839 ◽  
Author(s):  
Jeff Searl ◽  
Paul M. Evitts
Keyword(s):  
Contact Pressure ◽  
Air Pressure ◽  
Speaking Rate ◽  
Clear Speech ◽  
Speech Acoustics ◽  
Relationship Of ◽  
The Relationship ◽  
Speech Clarity ◽  
Normal Speech ◽  
Listener Ratings

Purpose The authors compared articulatory contact pressure (ACP), oral air pressure (Po), and speech acoustics for conversational versus clear speech. They also assessed the relationship of these measures to listener perception. Method Twelve adults with normal speech produced monosyllables in a phrase using conversational and clear speech. Target phonemes were /t, d, s, z, l, n/. ACP was measured at a point of articulatory contact; Po was sensed by a catheter open in the posterior oral cavity. Results ACP was increased to a greater extent in clear speech for /t, d, z/. Po was increased to a greater extent for /t, d/. Acoustic changes also occurred in terms of segment durations, speaking rate, and CV dB ratio. Regression analysis indicated that segment duration was the strongest predictor of listener ratings of speech clarity, followed by an index of articulatory effort and speaking rate. Conclusion Articulatory effort, as indexed by ACP, Po, and CV dB ratio, was increased to varying degrees depending on the consonant. Greatest changes occurred for /t, d/. Durational measures at both the segment and the phrase level were also important for predicting listener ratings of speech clarity.

Prediction of the Leakage Threshold for Hertzian Contact Seals: An Experimental Approach

2018 ◽  
Author(s):  
Jeroen Van Wittenberghe ◽  
John Vande Voorde
Keyword(s):  
High Pressure ◽  
Contact Pressure ◽  
Contact Area ◽  
Oil And Gas ◽  
Empirical Evaluation ◽  
Evaluation Criteria ◽  
Hertzian Contact ◽  
Surface Topology ◽  
Current Form ◽  
Leak Tightness

The prediction and evaluation of leakage and leak tightness is an important issue in a multitude of high-pressure applications, such as valves, flanges and threaded pipe connections that are used under extreme service conditions that occur in oil and gas exploration and production. Using Hertzian contact theory or finite element techniques it is possible to determine the local contact conditions at the seal on a macroscopic level (to wit the extent of the contact area and the contact pressure in this area). However, the leak tightness of such a contact depends also on the surface topology, which is a microscopic characteristic. Therefore, the assessment of leak tightness requires an evaluation criterion relating both scales. Empirical evaluation criteria have been postulated in the past, each with their own application domain. More recently the Persson method has been developed that models the contact area microscopically using contact models developed in the field of tribology. However, in its current form this model is limited to flat surfaces while in many applications, such as valves, O-ring seals or metal-to-metal seals of threaded pipe connections, the contact is Hertzian and the contact pressure distribution is not uniform but parabolic. This paper provides the experimental results that will be used to validate an extension of the Persson model to Hertzian contact seals. A set of samples for leakage experiments was produced with varying surface topology. The surface roughness of these samples is measured and the leakage behaviour under high pressure is evaluated. This paper focusses on the experimental evaluation of the influence of surface topology on leakage.

A Relationship Between Autocorrelation Length and Adhesive Friction Behavior of Rough Surfaces

2005 ◽  
Author(s):  
Yilei Zhang ◽  
Sriram Sundararajan
Keyword(s):  
Rough Surface ◽  
Spatial Information ◽  
Roughness Parameter ◽  
Hertzian Contact ◽  
Root Mean Square Roughness ◽  
Friction Behavior ◽  
The Real ◽  
Real Area Of Contact ◽  
Autocorrelation Length ◽  
Real Area

Autocorrelation Length (ACL) is a surface roughness parameter that provides spatial information of surface topography that is not included in amplitude parameters such as Root Mean Square roughness. This paper presents a statistical relation between ACL and the real area of contact, which is used to study the adhesive friction behavior of a rough surface. The influence of ACL on profile peak distribution is studied based on Whitehouse and Archard’s classical analysis, and their results are extended to compare profiles from different surfaces. With the knowledge of peak distribution, the real area of contact of a rough surface with a flat surface can be calculated using Hertzian contact mechanics. Numerical calculation shows that real area of contact increases with decreasing of ACL under the same normal load. Since adhesive friction force is proportional to real area of contact, this suggests that the adhesive friction behavior of a surface will be inversely proportional to its ACL. Results from microscale friction experiments on polished and etched silicon surfaces are presented to verify the analysis.

scholarly journals Extended Hertz Theory of Contact Mechanics for Case-Hardened Steels With Implications for Bearing Fatigue Life

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
Nikhil D. Londhe ◽  
Nagaraj K. Arakere ◽  
Ghatu Subhash
Keyword(s):  
Elastic Modulus ◽  
Fatigue Life ◽  
Contact Pressure ◽  
Effective Elastic Modulus ◽  
Hardened Steel ◽  
Hertzian Contact ◽  
Design Parameters ◽  
Case Hardening ◽  
Ball Bearings ◽  
Subsurface Stress

The analytical expressions currently available for Hertzian contact stresses are applicable only for homogeneous materials and not for case-hardened bearing steels, which have inhomogeneous microstructure and graded elastic properties in the subsurface region. Therefore, this article attempts to determine subsurface stress fields in ball bearings for graded materials with different ball and raceway geometries in contact. Finite element models were developed to simulate ball-on-raceway elliptical contact and ball-on-plate axisymmetric contact, to study the effects of elastic modulus variation with depth due to case hardening. Ball bearings with low, moderate, and heavy load conditions are considered. The peak contact pressure for case-hardened steel is always more than that of through-hardened steel under identical geometry and loading conditions. Using equivalent contact pressure approach, effective elastic modulus is determined for case-carburized steels, which will enable the use of Hertz equations for different gradations in elastic modulus of raceway material. Nonlinear regression tools are used to predict effective elastic modulus as a weighted sum of surface and core elastic moduli of raceway material and design parameters of ball–raceway contact area. Mesh convergence study and validation of equivalent contact pressure approach are also provided. Implications of subsurface stress variation due to case hardening on bearing fatigue life are discussed.

Influence of the Contact Pressure on the Rolling Resistance Moments in Dry Ball-Race Contacts

2014 ◽  
Vol 658 ◽  
pp. 305-310
Author(s):  
Alina Corina Dumitrascu ◽  
Gelu Ianus ◽  
Dumitru Olaru
Keyword(s):  
Theoretical Model ◽  
Contact Pressure ◽  
Rotational Speed ◽  
Ball Bearing ◽  
Rolling Resistance ◽  
Theoretical Models ◽  
Hertzian Contact ◽  
Experimental Methodology ◽  
Experimental Values ◽  
Good Agreement

Based on a theoretical model and an experimental methodology for defining the rolling resistance moments in a modified thrust ball bearing having only 3 balls, the authors experimentally investigated the influence of the Hertzian contact pressure on rolling resistance moments between a ball and a race. The experiments were realized with balls having diameters between 1.588 mm and 4.762 mm with maximum Hertzian pressure between 0.2GPa and 1GPa, operating for rotational speed between 60rpm to 210 rpm. The experiments evidenced that the measured values of the rolling resistance moments have higher values that the theoretical hysteresis and curvature rolling resistance moments for low contact pressure. By increasing of the contact pressure to 1GPa the experimental values for rolling resistance moments are in good agreement with the theoretical models.

Combustion Microstructures and Frictional Ignition Resistance of Ti-6Al-4V Titanium Alloy

2019 ◽  
Vol 944 ◽  
pp. 127-134
Author(s):  
Guang Bao Mi ◽  
Xu Huang ◽  
Jing Xia Cao ◽  
Bao Wang ◽  
Chun Xiao Cao
Keyword(s):  
Titanium Alloy ◽  
Contact Pressure ◽  
Heat Affected Zone ◽  
Ignition Temperature ◽  
Parabolic Law ◽  
Composite Oxides ◽  
Critical Ignition ◽  
Flow Pressure ◽  
Relationship Of ◽  
The Relationship

The effects of the contact pressure Pfric and the oxygen concentration c0 on the ignition resistance of Ti-6Al-4V were studied by friction in oxygen-enriched atmosphere. The relationship of Pfric-c0 was built to quantitatively describe the ignition resistance, the combustion microstructures were investigated by XRD, SEM and EDS. Further, the principle of improving the ignition resistance was proposed. It indicates that the relationship of Pfric-c0 obeys parabolic law. The c0 decreases by 4% when the Pfric increases from 0.1MPa to 0.25MPa, manifesting that the ignition resistance depends on c0 strongly (or equivalent flow pressure Peq). The ignition resistance of Ti-6Al-4V is 42.9% of that of TB12. When Peq varies from 0.1~0.5MPa, the critical ignition temperature Т* is approximate to 568~461K. Violent sparks form during frictional ignition. The low ignition resistance of Ti-6Al-4V probably results from not only the composite oxides of TiO2, Al2O3 and V2O5 generating during ignition which could not prevent the rapid interaction between Ti and O, but also the Al and V elements in the heat-affected zone which could not stop or slow the massive diffusion of O towards the alloy.

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