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FROM:
Moon M.W. (1,4), Jensen H.M. (2), Hutchinson J.W. (3), Oh K.H. (1), Evans A.G. (4)
(1) School of Material Science and Engineering, Seoul National University, San-56-1, Sillim-Dong, Kwanak-Gu, Seoul 151-744, South Korea
(2) Department of Solid Mechanics, Technical University of Denmark, Lyngby, DK-2800, Denmark
(3) Division of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA
(4) Princeton Materials Institute, Princeton University, NJ 08540, USA
“The characterization of telephone cord buckling of compressed thin films on substrates”, Journal of the Mechanics and Physics of Solids, Vol. 50, pp 2355-2377, 2002
ABSTRACT: The topology of the telephone cord buckling of compressed diamond-like carbon films (DLC) on glass substrates has been characterized with atomic force microscopy (AFM) and with the focused ion beam (FIB) imaging system. The profiles of the several buckles have been measured by AFM to establish the symmetry of each repeat unit, revealing similarity with a circular buckle pinned at its center. By making parallel cuts through the buckle in small, defined locations, straight-sided buckles have been created on the identical films, enabling the residual stress in the film to be determined from the profile. It has been shown that the telephone cord topology can be effectively modeled as a series of pinned circular buckles along its length, with an unpinned circular buckle at its front. The unit segment comprises a section of a full circular buckle, pinned to the substrate at its center. The model is validated by comparing radial profiles measured for the telephone cord with those calculated for the pinned buckle, upon using the residual stress in the film, determined as above. Once validated, the model has been used to determine the energy release rate and mode mixity, G(psi). The results for G(psi) indicate that the telephone cord configuration is preferred when the residual stress in the DLC is large, consistent with observations that straight-sided buckles are rarely observed, and, when they occur, are generally narrower than telephone cords. Telephone cords are observed in many systems, and can be regarded as the generic morphology. Nevertheless, they exist subject to a limited set of conditions, residing within the margin between complete adherence and complete delamination, provided that the interface has a mode II toughness low enough to ensure that the buckle crack does not kink into the substrate.
INTRODUCTION: Residually compressed thin films on thick substrates may buckle. The buckles propagate beneath the film if the induced energy release rate exceeds the interface fracture toughness. The associated mechanics has been documented (Evans and Hutchinson, 1984; Hutchinson et al., 1992, etc. etc.
The conditions at the stationary side and the circular front have been modeled and rationalized in terms of mode mixity and energy release rate (Hutchinson and Suo, 1992; Hutchinson, 2001; Jensen and Sheinman, 2001). The corresponding mechanics for telephone cord The purpose of this study is to gain some insight by performing measurements on thin films of diamond-like carbon (DLC) deposited onto nominally flat glass substrates and conducting a corresponding mechanics assessment. Such systems are The purpose of this study is to gain some insight by performing measurements on thin films of diamond-like carbon (DLC) deposited onto nominally flat glass substrates and conducting a corresponding mechanics assessment. Such systems are typically subject to high residual compression are less well developed. . . .
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