A study of 3D crack patterns and columnar jointing in corn starch
A study of 3D crack patterns and columnar jointing in corn starch
M.Sc. thesis, Unpublished, 2003.
Lucas Goehring
Department of Physics,
University of Toronto, 60 St. George St., Toronto, Ontario, Canada M5S 1A7.
The nature of columnar jointing has remained an enticing mystery
since the basaltic columns of the Giant's Causeway in N. Ireland
were first reported to science, over three hundred years ago. More
recently, this phenomena, which causes shrinkage cracks to form
into a quasi-hexagonal arrangement, has been shown to produce
columns in a wide variety of situations and media. This report
will focus on experiments investigating the nature of columnar
jointing in corn starch, which has been dried using an overhead
heat lamp. A study of the 3D nature of this pattern produces the
first qualitative description of the ordering process, whereby a
disorganized superficial crack pattern arranges itself into a
quasihexagonal crack pattern at depth. Experiments probing the
nature of the pattern in deep samples show that two distinct types
of coarsening can increase the pattern scale. The difference
between a slow, gradual shift in scale, and a sudden catastrophic
jump in scale is explained by assuming that a resistance to scale
change is inherent to this pattern. Such a hysteretic pattern may
answer a fundamental question of columnar jointing -- why the
columns are so regular in the direction of their growth. This
theory may be tested in other media, notably in a number of
suggested measurements on basaltic colonnades. Computer control
over the evaporation rate in a growing sample continues to be
worked on, as do experiments revealing the dynamics of this
pattern in an actively drying starch sample.
The Experimental Nonlinear Physics Group / Dept. of Physics / University of Toronto / 60 St. George St. Toronto, Ontario, Canada, M5S 1A7. Phone (416) 978 - 6810