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CATEGORIES:BPI Seminar Series
SUMMARY:The viscosities of partially molten materials unde
rgoing diffusion creep - John Rudge (University of
Cambridge)
DTSTART;TZID=Europe/London:20190214T113000
DTEND;TZID=Europe/London:20190214T123000
UID:TALK117328AThttp://talks.cam.ac.uk
URL:http://talks.cam.ac.uk/talk/index/117328
DESCRIPTION:Partially molten materials resist shearing and com
paction. This resistance \nis described by a fourt
h-rank effective viscosity tensor. When the tensor
\nis isotropic\, two scalars determine the resist
ance: an effective shear and \nan effective bulk v
iscosity. In this seminar\, calculations are prese
nted of \nthe effective viscosity tensor during di
ffusion creep for a 3D tessellation of \ntetrakaid
ecahedrons (truncated octahedrons). The geometry o
f the melt is \ndetermined by assuming textural eq
uilibrium. Two parameters \ncontrol the effect of
melt on the viscosity tensor: the porosity and th
e \ndihedral angle. Calculations for both Nabarro-
Herring (volume diffusion) \nand Coble (surface di
ffusion) creep are presented. For Nabarro-Herring
\ncreep the bulk viscosity becomes singular as the
porosity vanishes. This \nsingularity is logarith
mic\, a weaker singularity than typically assumed
in \ngeodynamic models. The presence of a small am
ount of melt (0.1% porosity) \ncauses the effectiv
e shear viscosity to approximately halve. For Cobl
e creep\, \nprevious modelling work has argued tha
t a very small amount of melt may \nlead to a subs
tantial\, factor of 5\, drop in the shear viscosit
y. Here\, a \nmuch smaller\, factor of 1.4\, drop
is obtained.\n
LOCATION:Open Plan Area\, BP Institute\, Madingley Rise CB3
0EZ
CONTACT:Catherine Pearson
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