Journal
PROCEEDINGS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES
Volume 471, Issue 2175, Pages -Publisher
ROYAL SOC
DOI: 10.1098/rspa.2014.0727
Keywords
adhesion; indentation; contact mechanics; surface tension
Categories
Funding
- U.S. Department of Energy, Office of Basic Energy Science, Division of Material Sciences and Engineering [DE-FG02-07ER46463]
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The surface tension of compliant materials such as gels provides resistance to deformation in addition to and sometimes surpassing that owing to elasticity. This paper studies how surface tension changes the contact mechanics of a small hard sphere indenting a soft elastic substrate. Previous studies have examined the special case where the external load is zero, so contact is driven by adhesion alone. Here, we tackle the much more complicated problem where, in addition to adhesion, deformation is driven by an indentation force. We present an exact solution based on small strain theory. The relation between indentation force (displacement) and contact radius is found to depend on a single dimensionless parameter: omega = sigma(mu R)(-2/3)((9 pi/4) W-ad)(-1/3), where sigma and mu are the surface tension and shear modulus of the substrate, R is the sphere radius and W-ad is the interfacial work of adhesion. Our theory reduces to the Johnson-Kendall-Roberts (JKR) theory and Young-Dupre equation in the limits of small and large omega, respectively, and compares well with existing experimental data. Our results show that, although surface tension can significantly affect the indentation force, the magnitude of the pull-off load in the partial wetting liquid-like limit is reduced only by onethird compared with the JKR limit and the pull-off behaviour is completely determined by omega.
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