Empirical relationship between interfacial shear stress and contact pressure in micro- and macro-scale friction

He, Xin; Liu, Zhong; Ripley, Lars B.; Swensen, Victoria L.; Griffin-Wiesner, Isaac J.; Gulner, Beatrice R.; McAndrews, Gabriel R.; Wieser, Raymond J.; Borovsky, Brian; Wang, Q. Jane; Kim, Seong H.

doi:10.1016/j.triboint.2020.106780

Cited by 30 publications

(19 citation statements)

References 50 publications

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“…This relationship has recently been proven to be valid within reasonable experimental error for both macroscopic and microscopic contacts (Figure 2). [29] In this recent study, it was shown that, if the surface roughness is smaller than the Hertzian deformation depth and surface roughening due to wear is negligible, the Hertzian contact area can be used for this calculation; if not, the effective contact area should be calculated from the surface roughness of the sliding track or measured independently during sliding. [29] Figure 2.…”

Section: A Experimental Approachesmentioning

confidence: 99%

“…[29] In this recent study, it was shown that, if the surface roughness is smaller than the Hertzian deformation depth and surface roughening due to wear is negligible, the Hertzian contact area can be used for this calculation; if not, the effective contact area should be calculated from the surface roughness of the sliding track or measured independently during sliding. [29] Figure 2. Empirical relationship between the interfacial shear stress (τ) due to kinetic friction and the average normal contact stress (σ) for (a) macroscopic sliding of a 3 mm dia.…”

Section: A Experimental Approachesmentioning

confidence: 99%

“…Thus, when these two values are to be compared, the magnitude of COF should be considered as a correction factor. [29] To be dimensionally correct, ∆𝑉𝑉 * or ∆𝑒𝑒 * in Eq. ( 3) should be reported in units of volume or length per molecule; if the gas constant (𝑅𝑅 = 8.314 J/mol⋅K) is used instead of the Boltzmann constant (𝑘𝑘 𝑏𝑏 ) in Eq.…”

Section: The Magnitude Of Activation Volume 4a Magnitudes Of Reported Activation Volumesmentioning

confidence: 99%

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Activation Volume in Shear-Driven Chemical Reactions

Martini

Kim

2021

Tribol Lett

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Interfacial shear-driven or shear-assisted chemical reactions play an important role in many engineering processes, including reactions between lubricant additives and the surfaces of mechanical components and fabrication of surface topographic features. Mechanistic studies of shear-driven chemical reactions often employ a mechanically assisted thermal-activation model from which a so-called activation volume can be defined. Activation volume is important because it quantifies the efficiency of interfacial shear to drive the reaction. Recent advancements in methods have enabled calculation of activation volume from both nano-and macro-scale experiments as well as simulations. However, the calculated volumes differ by orders of magnitude, even for the same reactant species, and the physical interpretations vary correspondingly. Here, we review how activation volume has been measured and interpreted for shear-driven reactions in the literature with the goal of guiding future efforts to understand and use this important parameter for engineering design through tribochemistry.

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Section: A Experimental Approachesmentioning

confidence: 99%

Section: A Experimental Approachesmentioning

confidence: 99%

Section: The Magnitude Of Activation Volume 4a Magnitudes Of Reported Activation Volumesmentioning

confidence: 99%

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Activation Volume in Shear-Driven Chemical Reactions

Martini

Kim

2021

Tribol Lett

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“…Based on the Hertzian contact mechanics, the average contact pressure was calculated to be 303 MPa. , The lateral force exerted to the sphere due to friction during the bidirectional motion of the substrate was measured with a strain gauge sensor which was calibrated in the expected friction force range. The coefficient of friction (COF) was calculated by using Amonton’s law (friction coefficient = friction force/normal load) . A dry nitrogen stream (H 2 O < 3 ppm, O 2 < 4 ppm based on the supplier’s specification) was mixed with another stream saturated with water vapor at room temperature to produce the friction test in a relative humidity (RH) of 50%.…”

Section: Methodsmentioning

confidence: 99%

“…The coefficient of friction (COF) was calculated by using Amonton's law (friction coefficient = friction force/normal load). 58 A dry nitrogen stream (H 2 O < 3 ppm, O 2 < 4 ppm based on the supplier's specification) was mixed with another stream saturated with water vapor at room temperature 59 to produce the friction test in a relative humidity (RH) of 50%. The humid nitrogen was continuously flowed over the sample at a flow rate of 2 L/min to maintain the constant humidity during the measurement.…”

Section: Methodsmentioning

confidence: 99%

Superhydrophilic Polymer Brushes with High Durability and Anti-fogging Activity

Fromel

Sweeder

Jang

et al. 2021

ACS Appl. Polym. Mater.

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Hydrophilic surface coatings have made it into commercial application as possible solutions for problems such as fogging, frosting, and biofouling. However, there is an inherent contradiction: superhydrophilic coatings can prevent these unwanted phenomena, but they are also readily dissolved by water. To address this longevity concern, the present work introduces a fully aqueous surface-initiated (SI) polymerization under ambient conditions for the facile formation of durable superhydrophilic polymer coatings. The aqueous SI photoinduced electron transfer reversible addition−fragmentation chain transfer polymerization (SI-PET-RAFT) approach developed herein uses water as a sole solvent and can be performed in an ambient air atmosphere. This circumvents traditional shortcomings in SI radical polymerization related to limited hydrophilic monomer solubility in organic solvents and oxygen tolerance. In addition, polymerization under mild yellow light eliminates possible substrate degradation that can occur with conventional thermal or UV-light treatment. The cationic, anionic, and zwitterionic polymer films engineered in this study show promise as functional materials with enhanced durability, demonstrated to effectively combat the challenge of surface fogging. The described approach is user-friendly, cost-and time-efficient, and scalable and produces efficient anti-fogging coatings that outperform commercial solutions in both optical quality and durability.

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Why is Superlubricity of Diamond‐Like Carbon Rare at Nanoscale?

Jang,

Colliton,

Flaih

et al. 2024

Small

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Hydrogenated diamond‐like carbon (HDLC) is a promising solid lubricant for its superlubricity which can benefit various industrial applications. While HDLC exhibits notable friction reduction in macroscale tests in inert or reducing environmental conditions, ultralow friction is rarely observed at the nanoscale. This study investigates this rather peculiar dependence of HDLC superlubricity on the contact scale. To attain superlubricity, HDLC requires i) removal of ≈2 nm‐thick air‐oxidized surface layer and ii) shear‐induced transformation of amorphous carbon to highly graphitic and hydrogenated structure. The nanoscale wear depth exceeds the typical thickness of the air‐oxidized layer, ruling out the possibility of incomplete removal of the air‐oxidized layer. Raman analysis of transfer films indicates that shear‐induced graphitization readily occurs at shear stresses lower than or comparable to those in the nanoscale test. Thus, the same is expected to occur at the nanoscale test. However, the graphitic transfer films are not detected in ex‐situ analyses after nanoscale friction tests, indicating that the graphitic transfer films are pushed out of the nanoscale contact area due to the instability of transfer films within a small contact area. Combining all these observations, this study concludes the retention of highly graphitic transfer films is crucial to achieving HDLC superlubricity.

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Empirical relationship between interfacial shear stress and contact pressure in micro- and macro-scale friction

Cited by 30 publications

References 50 publications

Activation Volume in Shear-Driven Chemical Reactions

Activation Volume in Shear-Driven Chemical Reactions

Superhydrophilic Polymer Brushes with High Durability and Anti-fogging Activity

Why is Superlubricity of Diamond‐Like Carbon Rare at Nanoscale?

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