Schedule Aug 17, 2003
Columnar Crack Patterns in Corn Starch
Stephen Morris (University of Toronto)

Co-authors: Lucas Goehring, Stephen W. Morris The well-known geophysical phenomenon of columnar jointing, occurring most spectacularly in the Giant's Causeway in N. Ireland, has inspired several theories describing the origin and evolution of quasihexagonal crack patterns. Observations of similar columns in diverse media such as glass, starch, sandstone, and ice suggest that this pattern-forming process is very general in nature, but most studies of columnar jointing have been confined to geological field work. To better understand hexagonal columnar jointing, we have desiccated corn starch under controlled laboratory conditions. Using a combination of X-ray tomography and destructive sampling, we are able, for the first time, to visualize the full 3D evolution of the pattern. We have studied the growth of the quasihexagonal pattern from a superficially disordered crack network, and how the pattern coarsens in response to changes in the crack front speed. We characterized the pattern with several statistical indices which describe its structure and relative disorder. These experiments can help discriminate between the various theoretical models of this interesting pattern forming process.

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