Discussion of “Measuring and Understanding Contact Area at the Nanoscale: A Review” (Jacobs, T. D. B., and Ashlie Martini, A., 2017, ASME Appl. Mech. Rev., 69(6), p. 060802)

2017 ◽  
Vol 69 (6) ◽  
Author(s):  
M. Ciavarella ◽  
A. Papangelo
Keyword(s):  
Continuum Mechanics ◽  
Contact Area ◽  
Contact Stiffness ◽  
Real Contact Area ◽  
Simulation Techniques ◽  
Multiple Contacts ◽  
In Situ Electron Microscopy ◽  
Fractal Roughness ◽  
Temperature Time

Jacobs and Martini (JM) give a nice review of direct measurement methods (in situ electron microscopy), as well as indirect methods (which are based on contact resistance, contact stiffness, lateral forces, and topography) for measurement of the contact area, mostly at nanoscale. They also discuss simulation techniques and theories from single-contact continuum mechanics, to multicontact continuum mechanics and atomistic accounting. As they recognize, even at very small scales, “multiple-contacts” case occurs, and a returning problem is that the “real contact area” is often an ill-defined, “magnification” dependent quantity. The problem remains to introduce a truncation to the fractal roughness process, what was called in the 1970s “functional filtering.” The truncation can be “atomic roughness” or can be due to adhesion, or could be the resolution of the measuring instrument. Obviously, this also means that the strength (hardness) at the nanoscale is ill-defined. Of course, it is perfectly reasonable to fix the magnification and observe the dependence of contact area, and strength, on any other variable (speed, temperature, time, etc.).

scholarly journals Measuring and Understanding Contact Area at the Nanoscale: A Review

2017 ◽  
Vol 69 (6) ◽  
Author(s):  
Tevis D. B. Jacobs ◽  
Ashlie Martini
Keyword(s):  
Continuum Mechanics ◽  
Contact Area ◽  
Contact Stiffness ◽  
Indirect Methods ◽  
Simulation Techniques ◽  
In Situ Electron Microscopy ◽  
Direct Measurements ◽  
True Contact Area ◽  
Single Contact

The size of the mechanical contact between nanoscale bodies that are pressed together under load has implications for adhesion, friction, and electrical and thermal transport at small scales. Yet, because the contact is buried between the two bodies, it is challenging to accurately measure the true contact area and to understand its dependence on load and material properties. Recent advancements in both experimental techniques and simulation methodologies have provided unprecedented insights into nanoscale contacts. This review provides a detailed look at the current understanding of nanocontacts. Experimental methods for determining contact area are discussed, including direct measurements using in situ electron microscopy, as well as indirect methods based on measurements of contact resistance, contact stiffness, lateral forces, and topography. Simulation techniques are also discussed, including the types of nanocontact modeling that have been performed and the various methods for extracting the magnitude of the contact area from a simulation. To describe and predict contact area, three different theories of nanoscale contact are reviewed: single-contact continuum mechanics, multiple-contact continuum mechanics, and atomistic accounting. Representative results from nanoscale experimental and simulation investigations are presented in the context of these theories. Finally, the critical challenges are described, as well as the opportunities, on the path to establishing a fundamental and actionable understanding of what it means to be “in contact” at the nanoscale.

Study on Identification of Contact Stiffness Considering Surface Roughness

2014 ◽  
Vol 1017 ◽  
pp. 441-446 ◽  
Author(s):  
Kyoko Nakamura ◽  
Haruhisa Sakamoto
Keyword(s):  
Surface Roughness ◽  
Contact Area ◽  
Quantitative Measurement ◽  
Experimental Approach ◽  
Contact Stiffness ◽  
Real Contact Area ◽  
Special Device ◽  
Real Contact ◽  
Dominant Configuration ◽  
Simplified Calculation

In previous study, the quantitative measurement method of contact stiffness of the joint considering real contact area is developed by experimental approach. However, the measurement of contact stiffness needs special device and skillful measuring technique. Therefore, in this paper, simplified calculation method with material properties and profile data of surface roughness obtained by profilometer is considered. As a result, real contact area, contact stiffness and contact spring stiffness calculated from specific wavelength of rough surface are near agreement with experimental value. Hence, it is revealed that there is dominant configuration in surface roughness.

scholarly journals Mechanics Analysis of Rough Surface Based on Shoulder-Shoulder Contact

2021 ◽  
Vol 11 (17) ◽  
pp. 8048
Author(s):  
Qiuping Yu ◽  
Jianjun Sun ◽  
Zhengbo Ji
Keyword(s):  
Rough Surface ◽  
Contact Area ◽  
Rough Surfaces ◽  
Geometric Model ◽  
Mechanical Analysis ◽  
Real Contact Area ◽  
Mechanics Model ◽  
Porosity Reduction ◽  
Fractal Roughness ◽  
Fractal Characteristics

Proper methods and models for mechanical analysis of rough surface can improve the theory of surface contact. When the topography parameters of two rough surfaces are similar, the contact should be considered shoulder-shoulder rather than top-top. Based on shoulder-shoulder contact and fractal characteristics, the geometric model for asperity and contact mechanics model for rough surfaces are established, and the deformation of asperity, the real contact area and contact load of sealing surface are discussed. The effects of contact pressure p and topography parameters (fractal dimension D and fractal roughness G) on the variation of porosity and contact area ratio Ar/A0 are achieved. Results show that with the increase of p, larger D and smaller G corresponds to larger initial porosity but faster and larger decrease of porosity; with the increment of D, porosity increases first and then decreases, and smaller G corresponds to larger porosity reduction; as G becomes bigger, porosity increases, and larger D corresponds to larger porosity difference and change. With the addition of p, Ar/A0 increases, and the variation of Ar/A0 is closer to linearity and less at smaller D and larger G; with the increase of D, Ar/A0 increases gradually, and the growth rate is bigger at smaller G and bigger p; as G becomes bigger, Ar/A0 declines, and it declines more gently at smaller D and p. The influence of D on Ar/A0 is greater than that of G. The results can provide the theoretical basis for the design of sealing surfaces and the research of sealing or lubrication technologies of rough surfaces.

Contact stiffness of mating surfaces of parts under dynamic loading

2020 ◽  
pp. 57-60
Author(s):  
M.M. Matlin ◽  
V.A. Kazankin ◽  
E.N. Kazankina ◽  
A.I. Mozgunova
Keyword(s):  
Dynamic Loading ◽  
Contact Area ◽  
Contact Stiffness ◽  
Dynamic Contact ◽  
Real Contact Area ◽  
Contact Loading ◽  
The Real ◽  
Real Contact ◽  
Nominal Pressure ◽  
Plastic Hardness

The dependences of the relative real contact area of the flat contacting surfaces of steel parts on the nominal pressure under dynamic contact loading are studied. It is determined, that the real contact area under dynamic loading is less than under static one. Keywords dynamic plastic hardness, contact approach, real contact area, contact stiffness. [email protected]

scholarly journals Precise Correlation of Contact Area and Forces in the Unstable Friction between a Rough Fluoroelastomer Surface and Borosilicate Glass

Materials ◽  
2020 ◽  
Vol 13 (20) ◽  
pp. 4615
Author(s):  
Chao Wang ◽  
Shabnam Z. Bonyadi ◽  
Florian Grün ◽  
Gerald Pinter ◽  
Andreas Hausberger ◽  
...  
Keyword(s):  
Contact Area ◽  
Low Frequency ◽  
Dynamic Contact ◽  
High Amplitude ◽  
Partial Slip ◽  
Real Contact Area ◽  
Stick Slip ◽  
The Real ◽  
Real Contact

Stick-slip friction of elastomers arises due to adhesion, high local strains, surface features, and viscous dissipation. In situ techniques connecting the real contact area to interfacial forces can reveal the contact evolution of a rough elastomer surface leading up to gross slip, as well as provide high-resolution dynamic contact areas for improving current slip models. Samples with rough surfaces were produced by the same manufacturing processes as machined seals. In this work, a machined fluoroelastomer (FKM) hemisphere was slid against glass, and the stick-slip behavior was captured optically in situ. The influence of sliding velocity on sliding behavior was studied over a range of speeds from 1 µm/s to 100 µm/s. The real contact area was measured from image sequences thresholded using Otsu’s method. The motion of the pinned region was delineated with a machine learning scheme. The first result is that, within the macroscale sticking, or pinned phase, local pinned and partial slip regions were observed and modeled as a combined contact with contributions to friction by both regions. As a second result, we identified a critical velocity below which the stick-slip motion converted from high frequency with low amplitude to low frequency with high amplitude. This study on the sliding behavior of a viscoelastic machined elastomer demonstrates a multi-technique approach which reveals precise changes in contact area before and during pinning and slip.

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