Elastic sheets: Cracks by design

Abstract

Different methods exist to control fracture in thin media in order to produce some desired shape or curved edge. Commonly, inhomogeneities are placed along a specific path to guide a fracture, such as scoring a material's surface or introducing a sequence of perforations. In some circumstances, the ability to guide fractures without altering the material is advantageous or even necessary, and could provide a key design tool in areas such as flexible electronics, thin films and monolayer materials. Writing in Nature Materials, Mitchell, Irvine and colleagues explore the possibility of guiding crack paths in thin, elastic sheets by draping them on surfaces with non-zero Gaussian curvature1. The out-of-plane elastic deformation imposed by the surface curvature causes an inhomogeneous stress distribution within the sheet. If a small crack is introduced, the pre-load in the membrane can cause the fracture to grow spontaneously. Depending on how the substrate geometry is chosen, the crack growth can be made to conform to a curved path and possibly arrest after a desired crack length has been reached. This opens up the possibility of a new methodology for incising two-dimensional shapes from sheets by fracturing them over a tailored bumpy substrate surface.