Creases on the interface between two soft materials

Theory and experiment are presented to show that an interface between two soft materials under compression can form creases, a type of bifurcation distinct from wrinkles. While creases bifurcate from a state of flat interface by a deformation localized in space and large in amplitude, wrinkles bifurcate from a state of flat interface by a deformation nonlocal in space and infinitesimal in amplitude. The interfacial creases set in at a lower critical compression than interfacial wrinkles, but higher than surface creases. The condition for the onset of interfacial creases is scale-free, and is calculated in terms of elastic moduli, pre-strains and applied strains.

http://pubs.rsc.org/en/content/articlelanding/2013/sm/c3sm51512e#!divAbstract 

Lihua Jin, Dayong Chen, Ryan C. Hayward, Zhigang Suo. Creases on the interface between two soft materials. Soft Matter 10, 303-311 (2014).