Materials Science

Bursting the Balloon

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Science  11 Jan 2002:
Vol. 295, Issue 5553, pp. 235
DOI: 10.1126/science.295.5553.235f

When a crack propagates through a solid, it typically takes a straight-line path, as this requires the least amount of work from the system. However, when a balloon is popped, it shatters into fragments that have wavy patterned edges. Deegan et al. have constructed an apparatus to study crack propagation in a controlled manner. A series of notches are cut into a rectangular sheet of rubber, and these are annealed to prevent fracture at these points. The projecting tabs are clamped, and the sample is then stretched in both directions, with the greater tension in the short direction of the sheet. Piercing the rubber with a pin generates a crack that propagates along the long direction. At low strains there is an initial kink in the crack, but usually it straightens, following the centerline of the sample. Above a critical strain, the crack oscillates around the centerline with a wavelength that depends on the strain values in both directions. The authors rule out stress-induced crystallization of the rubber and out-of-plane motions as the cause of the instability, and instead show that it can be characterized as a Hopf bifurcation. — MSL

Phys. Rev. Lett.88, 014304 (2002).

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