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Spiraling Cracks in Thin Sheets

Abstract : Opening a package made of a thin film is not always a satisfying experience. The crack is not easily controlled even though we try to guide it with our hands. This “freedom” for the crack propagation is connected with the many possibilities of thin sheets to deform. Indeed, deformation and fracture are highly related because deformation is the source of the energy required to propagate a crack. In this way, finding and explaining regular crack paths in thin sheets improve our understanding of the fracture of these objects. In previous scientific works, regular crack paths in brittle thin sheets have been reported. We can mention convergent tears obtained by peeling or tearing a flap of a thin sheet; also it is possible to find oscillatory cracks when a thin sheet is cut through by a moving blunt object. In this work we present two very robust, reproducible, divergent families of cracks paths in a brittle material (bi-oriented polypropylene, BOPP, usually used in packaging). These two final crack paths are characterized as similar logarithmic spirals although they are the outcomes of two very different set-ups. A first logarithmic spiral is the result of propagate only one crack by pushing an edge of a thin sheet, in this case the crack propagates because the material is been stretched and therefore the energy associated with the fracture propagation is “stretching energy”. In the second spiral experiment, we propagate only one crack on the same material, but now we are tearing up in such a way that the energy, feeding the crack, comes from out of plane deformation. This last procedure not only results in a spiraling regular crack, but also in a beautiful and very complex out-of-plane structure of the tear.
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Submitted on : Wednesday, January 5, 2011 - 11:37:56 AM
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  • HAL Id : pastel-00552045, version 1


Victor Romero. Spiraling Cracks in Thin Sheets. Mechanics of materials [physics.class-ph]. Université Pierre et Marie Curie - Paris VI, 2010. English. ⟨pastel-00552045⟩



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