The physical rules of tearing a packaging or a piece of paper are not completely elucidated despite this is a common phenomenon in daily life. When opening a package, fracture seems to propagate following unpredictable directions even if we use a similar form of pulling. To overcome this issue, packaging industry developed a variety of strategies aimed at weakening locally the packaging, thus favoring the tearing trajectory along a desired path. In our lab we are investigating how the presence of a rigid and straight object, a ruler, guides the fracture of a thin sheet within a wide range of pulling directions. In the case of thin isotropic brittle sheets, a simple geometrical analysis shows that fracture follows the direction of a tearing vector, which differs significantly from the pulling direction. In addition to geometry, fold energy or material anisotropy has to be implemented in the case of thick or anisotropic sheets, to predict the direction of propagation. A generalization of the Wuff’s type construction accounts successfully for the experimental results. This work is on progress.
A. Ibarra, J.F. Fuentealba, J. Bico, B. Roman and F. Melo, Guided Tearing: the ruler cases, in progress.