Evolution of wrinkles in hard films on soft substrates.

A compressively strained film on a substrate can wrinkle into intricate patterns. This Rapid Communication studies the evolution of the wrinkle patterns. The film is modeled as an elastic nonlinear plate and the substrate a viscoelastic foundation. A spectral method is developed to evolve the nonlinear system. When the initial film strains are isotropic, the wrinkles evolve into a pattern with a motif of zigzag segments, in random orientations. When the initial film strains are anisotropic, the wrinkles evolve to an array of herringbones or stripes. The zigzag segments select a width, a length, and an elbow angle that minimize the total elastic energy.