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Origins and Uses of Wrinkles, Creases, Folds

July 17, 2013
Three ruga states and how they form

A phase diagram shows the amount of compressive strain needed to create wrinkles, creases and folds in rubbery materials. The purple area denotes the wrinkle state and the aqua areas are two crease states. The spot marked “R” denotes folding. Credit: Kim lab/Brown University

Engineers from Brown University, including postdoctoral researcher Mazen Diab,  have mapped out the amounts of compression required to cause wrinkles, creases, and folds to form in rubbery materials. The findings could help engineers control the formation of these structures, which can be useful in designing nanostructured materials for flexible electronic devices or surfaces that require variable adhesion.

“When a rubbery material is compressed and reaches a critical load, it experiences instability and forms surface patterns like wrinkles, creases, or folds,” said Mazen Diab, a postdoctoral researcher in Brown’s School of Engineering and the paper’s first author. “We’re studying how each of those states forms.”

While most of us might use the terms wrinkle, crease, and fold almost interchangeably, engineers recognize distinct properties in each of those states. As defined by the Brown researchers, the wrinkle state is when peaks and troughs start to form on the surface, like waves on the ocean. The crease state is when a distinctly sharp groove is formed on the surface. A fold occurs when the areas on either side of the wrinkle trough begin to touch, forming hollow channels beneath the surface plane of the material.

The researchers refer to these states collectively as “ruga” states, a term originating from Latin and often used in anatomy to describe wrinkle formations in the body such as on the stomach or the roof of the mouth.

Read more of Kevin Stacey's story about wrinkles, creases, and folds.