Adhesion-Induced Instability in Asperities |
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Authors: | M S Bobji Shijo Xavier U B Jayadeep C S Jog |
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Affiliation: | (1) Department of Mechanical Engineering, Indian Institute of Science, Bangalore, India;(2) Structural Design and Engineering Division, Vikram Sarabhai Space Centre, Trivandrum, India;(3) Department of Mechanical Engineering, National Institute of Technology Calicut, Calicut, India |
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Abstract: | Adhesive forces between two approaching asperities will deform the asperities, and under certain conditions this will result
in a sudden runaway deformations leading to a jump-to-contact instability. We present finite element-based numerical studies
on adhesion-induced deformation and instability in asperities. We consider the adhesive force acting on an asperity, when
it is brought near a rigid half-space, due to van der Waals interaction between the asperity and the half-space. The adhesive
force is considered to be distributed over the volume of the asperity (body force), thus resulting in more realistic simulations
for the length scales considered. Iteration scheme based on a “residual stress update” algorithm is used to capture the effect
of deformation on the adhesion force, and thereby the equilibrium configuration and the corresponding force. The numerical
results are compared with the previous approximate analytical solutions for adhesion force, deformation of the asperity and
adhesion-induced mechanical instability (jump-to-contact). It is observed that the instability can occur at separations much
higher, and could possibly explain the higher value of instability separation observed in experiments. The stresses in asperities,
particularly in case of small ones, are found to be high enough to cause yielding before jump-to-contact. The effect of roughness
is considered by modeling a spherical protrusion on the hemispherical asperity. This small-scale roughness at the tip of the
asperities is found to control the deformation behavior at small separations, and hence are important in determining the friction
and wear due to the jump-to-contact instability. |
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