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FROM:
Takei, A. (1), Jin, L. (2), Hutchinson, J. W. (2) and Fujita, H. (1)
(1) Institute of Industrial Science, The University of Tokyo, Japan
(2) School of Engineering and Applied Sciences, Kavil Institute, Harvard University, Cambridge, Massachusetts, USA
“Ridge localizations and networks in thin films compressed by the incremental release of a large equi-biaxial pre-stretch in the substrate”, Advanced Materials, Vol. 26, pp 4061–4067, 2014
PARTIAL INTRODUCTION: The intriguing buckling patterns exhibited by bilayer systems composed of a thin stiff film bonded to a thick elastomeric sub- strate have been studied extensively in recent years both experi- mentally and theoretically. Under compression, the film is constrained by the substrate and buckles with a wavelength that is usually large compared to the film thickness, yet small com- pared to the substrate thickness. The most common patterns observed are the sinusoidal wrinkle mode when compression in one direction is dominant,[1] and the herringbone[2,3] and lab- yrinth[2–4] modes when compression is equi-biaxial. The present paper is part of the ongoing research effort in the soft-materials community to produce and manipulate specific buckling pat- terns.[5,6] Most of the previous work has focused on buckling patterns of bilayer systems under small compression. Recent work, however, has demonstrated that large compression of a bilayer system can engender other surface patterns such as period-doubling[7] and folding,[8,9] opening the way for the crea- tion of a wider array of surface patterns. These post-wrinkling modes involve the large strain behavior of the substrate and geometrical non-linearity of the films in an essential way. The focus of the present paper is on the most recent of the post-wrinkling modes to be discovered, the ridge localization mode. While folds and creases protrude into the substrate, the ridge is a large amplitude localization that pushes out from the substrate. This mode should be characterized as a localization because the large amplitude of the ridge is fed by flattening the nearby wrinkle undulations resulting in ridges that are sepa- rated from each other by expanses of relatively flat film. Thus, a distinct feature of the transition from wrinkles to ridges is the abrupt increase of spacing from crest to crest. The ridge localization was predicted to occur,[10] and has been observed experimentally,[5,6,11] only when a relatively large pre-stretch was imposed on the elastomeric substrate prior to film attachment. Controlled incremental release of the pre-stretch of the thick substrate then imposes compression on the film, which drives buckling. . . .
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