**APL 2008 Abstract**

**A parameter study of separation modes of adhering microcontacts
**

Yan Du, George G. Adams, Nicol E. McGruer, and Izhak Etsion

Summary

A finite element model was developed to study adhesion of elastic-plastic microcontacts in a previous investigation. An interesting result
was the identification of two distinct separation modes, i.e. brittle and ductile separation. In the current study, that model is used to conduct
a series of simulations to determine the influence of four non-dimensional parameters (including the maximum load parameter) on the contact
and on the separation modes. The results show that the parameter S (the ratio of the theoretical stress to the hardness) and a parameter
representing the loading level are the most important. Smaller S can only lead to brittle separation, while larger S can cause either separation
mode depending on load level. Ductile separation is more likely to occur at smaller load and brittle separation at greater load. The transition
between the two separation modes occurs at about S=1.2 (for a load level of 30) which corresponds to the theoretical stress for adhesion
being 20% greater than the hardness. This result is qualitatively similar to the existing simplified analytical models, in that the adhesion energy,
the hardness, and the loading level play important roles in the occurrence of ductile separation. However there are important quantitative
differences. Comparisons are also made with molecular dynamics simulations of a contact and with a fracture mechanics model of crack
propagation.
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