24 October 2003Research Away Day David Healy

1
An investigation into grain-scale interaction of
brittle cracking and grain-boundary diffusion

• 1. Scientific Problem
• crack propagation through grains perturbs the
  stress field grain boundary diffusion (GBD)
  requires a heterogeneous stress field for
  chemical potential gradients
• GBD can lead to increased normal stresses cracks
  propagate when yield strength exceeded
• physical and chemical interaction between
  brittle and plastic mechanisms how does this
  work ?
• 2. Importance/Relevance
• earthquake rupture involves cataclasis which may
• promote GBD i.e. so-called reaction softening
• upper crustal earthquakes may be controlled by
  alternating
• cycles of brittle cracking and GBD
• metamorphic reactions via coupled cracking GBD
  promoting
• fluid movement
• 3. Methods
• Theoretical analysis leading to 2-D and 3-D
  numerical models
• monomineralic aggregates then polymineralic
• Experiments on simple analogue materials (e.g.
  K-Alum, NaClO3, gypsum)
• ? stress measurements at grain-scale
  measure elastic strains via neutron diffraction
  or X-rays
• Observations of microstructures in rocks
  collected from natural fault zones

horsetail structure
grt
100?m
hbl spl
Straume Austrheim
24 October 2003 Research Away Day
David Healy