Topic
Contact area
About: Contact area is a research topic. Over the lifetime, 12358 publications have been published within this topic receiving 256401 citations. The topic is also known as: contact patch & contact region.
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TL;DR: In this article, the authors used a three-axis device to generate topographic images without having to move the sample, which allowed them to determine precisely the actual tip-sample contact area, while performing accurate continuous quantitative quasistatic load measurement and simulation.
Abstract: On the nanometre scale, the actual indenter-material contact area must be carefully determined to obtain reliable values of mechanical properties from an indentation test. On this scale, the contact area is greatly affected by the geometrical tip defect and by the possible formation of plastic pile-up (or sink-in) around the indent. Parameters such as local surface roughness and heterogeneity in surface and in thickness make it di5dt to conduct and to interpret nanoindentation tests. A new method, which couples nanoindentation experiments and imaging procedures, has been developed. Nanoindentation tests and topographic images are performed with a surface force apparatus developed in our laboratory. The important point of our method is the ability of our three-axis device to generate topographic images without having to move the sample. This allows us to determine precisely the actual tip–sample contact area, while performing accurate continuous quantitative quasistatic load measurement and simult...
173 citations
TL;DR: In this article, an analysis of the forces of adhesion of small particles to surfaces, most specifically as applied to semiconductor surfaces, was carried out and it was shown that the van der Waals forces can increase as a function of time due to particle and/or surface deformation which increases the contact area.
Abstract: This paper constitutes an analysis of the forces of adhesion of small particles to surfaces, most specifically as applied to semiconductor surfaces. The primary forces of adhesion of small, less than 50 μm diam particles on a dry surface are van der Waals forces. These van der Waals forces of adhesion can increase as a function of time due to particle and/or surface deformation which increases the contact area; micron‐size particles can be held to surfaces by forces exceeding 100 dyn, which corresponds to pressures of 109 dyn/cm2 or more. Total forces of adhesion for micron‐size particles exceed the gravitational force on that particle by factors greater than 106. Electrostatic forces only become important and predominate for particles larger than 50 μm diam. Immersion of the adhered particle system can, in some cases, greatly reduce the total adhesion force, first by shielding of the electrostatic and van der Waals attractions, and also by adding double layer repulsion because of dipolar alignment of liquid molecules or dissolved ions at the surfaces. Double layer interactions may, however, also add to the attractive forces if dipoles align properly for attraction. An important consideration is the possibility that if the particles are not removed by the liquid immersion, then a liquid bridge can be formed by capillary action between the particle and surface upon removal from the liquid. This would add a very large capillary force to the total force of adhesion. This capillary force has been shown to remain, in some cases, even when the system is baked at above the liquid boiling point for more than 24h. Removal of these small particles from surfaces is in theory possible but is in practice extremely difficult. It is clear that emphasis should be placed on prevention of particle deposition rather than on counting on achieving subsequent removal.
173 citations
TL;DR: Comparison with data derived from AFM force-indentation curves showed that the experimentally measured contact area for spherical tips agrees well with predicted values, whereas for pyramidal tips, the contact area can be grossly underestimated at forces larger than ∼0.2 nN leading to a greater than two-fold overestimation of elasticity.
Abstract: Atomic force microscopy (AFM) is widely used for measuring the elasticity of living cells yielding values ranging from 100 Pa to 100 kPa, much larger than those obtained using bead-tracking microrheology or micropipette aspiration (100–500 Pa). AFM elasticity measurements appear dependent on tip geometry with pyramidal tips yielding elasticities 2–3 fold larger than spherical tips, an effect generally attributed to the larger contact area of spherical tips. In AFM elasticity measurements, experimental force–indentation curves are analyzed using contact mechanics models that infer the tip–cell contact area from the tip geometry and indentation depth. The validity of these assumptions has never been verified. Here we utilize combined AFM–confocal microscopy of epithelial cells expressing a GFP-tagged membrane marker to directly characterize the indentation geometry and measure the indentation depth. Comparison with data derived from AFM force–indentation curves showed that the experimentally measured contact area for spherical tips agrees well with predicted values, whereas for pyramidal tips, the contact area can be grossly underestimated at forces larger than ~ 0.2 nN leading to a greater than two-fold overestimation of elasticity. These data suggest that a re-examination of absolute cellular elasticities reported in the literature may be necessary and we suggest guidelines for avoiding elasticity measurement artefacts introduced by extraneous cantilever–cell contact.
172 citations
TL;DR: In this article, it was shown that both the normal and tangential stresses play a part in the deformation of the metallic junctions formed at the interface, and the detailed behaviour of the junctions during the early stages of the sliding process may be expressed quantitatively in terms of von Mises's criterion for plastic deformation under combined normal and Tangential stresses, and there is good agreement between the theoretical relation and the experimental observations.
Abstract: Simultaneous measurements have been made of the friction and adhesion of steel sliding on indium in air. The results show that both the normal and tangential stresses play a part in the deformation of the metallic junctions formed at the interface. When the surfaces are first placed in contact, a minute tangential force is required to initiate relative motion between the slider and the indium surface, since the junctions are already plastic under the applied load. As relative motion proceeds, the region of contact grows with a corresponding increase in the tangential force and the adhesive force. An upper steady state is reached where the tangential force increases more rapidly than the rate of growth of the region of contact and sliding on a macroscopic scale occurs. The detailed behaviour of the junctions during the early stages of the sliding process may be expressed quantitatively in terms of von Mises's criterion for plastic deformation under combined normal and tangential stresses, and there is good agreement between the theoretical relation and the experimental observations. The results emphasize the reality of the cold welding process which occurs at the points of intimate contact when metal surfaces are placed together. The metallic junctions so formed are responsible both for the friction and the adhesion observed. Lubricant films diminish the amount of metallic contact and so lead to a reduction in the friction and adhesion.
172 citations
TL;DR: In this article, an analysis of the elastic recovery of a scratch after contact with a tip was performed using the standard indentation laws, which can be used to analyse the geometry of the scratches left by a moving tip on the surface of a viscoelastic viscoplastic body such as a commercial grade of cast polymethylmethacrylate (PMMA).
171 citations