Adhesion Map for Thin Films
Guangxu Li (Texas Instruments), Kai-Tak Wan (Northeastern University)
Mechanics of Thin Films and Multilayered Structures
Tue 9:00 - 10:30
Salomon 203
Theoretical models are available for two elastic spheres in adhesion contact. The DMT-limit refers to small and hard spheres with an ideal intersurface force (or disjioining pressure) of infinite range but small magnitude, while the JKR-limit corresponds to large and soft spheres with intersurface forces of zero-range but infinite magnitude. Adhesion trajectories are distinctly different at the two extremes. The Tabor’s parameter, Ta, is defined to gauge the JKR-DMT transition for spheres of intermediate size and stiffness with surface forces of intermediate and finite range and magnitude. These models, though meeting much success in a wide spectrum of materials in the past decades, are not applicable to thin films. A thin film conforms to the surface geometry when adheres to a rigid substrate, leaving negligible compression within the contact, contrasting the large Hertz compressive stress in case of adhering spheres. In this paper, we consider a circular freestanding film clamped at its periphery that adheres to the planar surface of a cylindrical punch. External tension, F, applied to the punch raises it by a vertical displacement of w, and detaches the membrane by shrinking the contact circle of radius, c. The relations between (F,w,c) as a function of range and magnitude of the intersurface force are derived for the JKR-limit, DMT-limit and the JKR-DMT transition. A new Tabor’s parameter is defined for adhesion-delamination of thin films under mixed bending-stretching deformation. “Pull-off” or spontaneous detachment at critical (F*,w*,c*) are also found. New adhesion map for thin films, similar to the classical map for solid spheres, is constructed to distinguish different regimes of JKR, DMT, JKR-DMT transition, for mixed bending-stretching and fixed-load / fixed grips loading.