Isometric immersions, energy minimization and self-similar buckling in   non-Euclidean elastic sheets
  The edges of torn plastic sheets and growing leaves often display hierarchical buckling patterns. We show that this complex morphology (i) emerges even in zero strain configurations, and (ii) is driven by a competition between the two principal curvatures, rather than between bending and stretching. We identify the key role of branch-point (or "monkey-saddle") singularities in generating complex wrinkling patterns in isometric immersions, and show how they arise naturally from minimizing the elastic energy. 
John Gemmer, Eran Sharon, Toby Shearman and Shankar C. Venkataramani
cond-mat.soft math.DG nlin.PS