The edge of a torn plastic sheet forms
a complex three-dimensional fractal
shape. We have found that the shape
results from a simple elongation of the sheet
in the direction along its edge. Natural
growth processes in some leaves, flowers
and vesicles could lead to a similar elongation and hence to the generation of
characteristic wavy shapes.
We used rectangular plastic sheets pulled
from the sides (in the y-direction) to generate a steadily travelling crack (in the xdirection). The high stresses near the crack
tip produce an irreversible plastic deformation of the sheet and, as they are relieved,
the deformed sheet is free to relax and to
adopt a new shape in space.