IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Tribology Wednesday Sessions
       Session TR+SS-WeM

Paper TR+SS-WeM1
Bonding and Debonding in Nanometer-Scale Viscoelastic Contacts

Wednesday, October 31, 2001, 8:20 am, Room 132

Session: Fundamentals of Tribology & Adhesion
Presenter: M. Giri, University of Maine
Authors: M. Giri, University of Maine
D.B. Bousfield, University of Maine
W.N. Unertl, University of Maine
Correspondent: Click to Email
Contact to viscoelastic materials, unlike elastic or elastomeric materials, are poorly understood, primarily because of the hysteretic effects caused by the time dependent mechanical properties. We present a quantitative analysis of contacts to viscoelastic materials, specifically crosslinked styrene-butadiene and uncrosslinked styrene-acrylate copolymers. Contacts were made with ultra-low load indentation using diamond probes of various axisymmetric shapes. Both creep and loading-unloading (bonding-debonding) measurements were made for penetration depths ranging from a few nanometers up to a few micrometers. This data was analyzed using the cohesive zone model recently developed by Hui and coworkers.@footnote 1@ This model demonstrates that the most information that can be extracted from a contact experiment is the Mode I Stress Intensity Functional K@sub I@. We show that no knowledge of the interfacial bonding mechanism is required to determine K@sub I@ from the displacement versus load data. In effect, K@sub I@ is analogous to the rate constant of a chemical reaction. Its measurement does not require knowledge of the bonding mechanism, but once measured, it can be used to test models of the mechanism. We illustrate this by testing the widely used bonding-debonding theory of Schapery@footnote 2@ for propagation of cracks at viscoelastic interfaces. We show that this model is inadequate to explain our results and attribute this failure to the assumption of a rate-independent interaction potential. @FootnoteText@ @footnote 1@Y.Y. Lin, C.K. Hui, J.M. Baney, J. Phys. D: Appl. Phys. 32 (1999) 2250. @footnote 2@R.A. Schapery, Intl. J. Fracture 39 (1989) 163.