HR: 14:00h
AN: T33F-02 INVITED [Abstracts]
TI: Deformation-Induced Grain Boundary Wetting and its Effects on the Acoustic and Rheological Properties
of Partially Molten Rock Analogue
AU: * Takei, Y
EM: ytakei@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, Univ. of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032
Japan
AB:
An experimental study
was performed to investigate the
effects of deviatoric stress on the
microstructure of partially molten
polycrystalline aggregates.
Borneol (organic crystal) + melt system
having an eutectic temperature of 43°C
and a moderate dihedral angle
was used as a partially molten rock analogue.
Large samples (70mm cube) having melt fractions of 0.089-0.22
were deformed ductilely under a uniform pure shear stress
(shear strain rate = ~ 0.8-7× 10-7 s-1),
while monitoring the sample microstructure in situ
using ultrasonic shear waves.
Each sample was deformed repeatedly by changing
the principal stress direction,
resulting in the microstructural changes well detectable
under the microscope.
The most remarkable features of
the stress- and/or deformation-induced microstructural changes
are enhanced grain-boundary wetting,
enhanced grain coarsening, and
formation of large (~ sample scale)
melt sheet parallel to the shear plane,
which is an assembly of completely wetted two-grain boundaries
at the microscopic scale.
Significant changes in the elastic, anelastic, and viscous properties
associated with these microstructural changes
were observed.
Grain-boundary contiguity,
which is defined by the ratio of grain-to-grain contact area
relative to the total surface area of each grain,
is the essential geometric
factor determining the macroscopic mechanical properties
of solid-liquid composites.
Anisotropy of grain contact is
described by contiguity tensor.
Contiguity can be used as an internal state variable
to describe the microstructural processes in the grain scale
and relate them to the macroscopic dynamics of the composites.
The present experimental results
on the equilibrium and dynamic microstructures
were analyzed quantitatively
through measurements of contiguity.
Based on the obtained microstructural and mechanical data,
the relative roles of melt fraction and contiguity
in elasticity, anelasticity, and viscosity
were assessed quantitatively.
Interaction between microstructural processes
and macroscopic dynamics can be treated
by using a constitutive mechanical relation
including contiguity as a state variable
and also using evolution law of contiguity.
A detailed picture of growth and healing
of grain boundary melt films
in response to loading cycles,
which was obtained through the velocity monitoring,
plays an important role for establishing the evolution
law of contiguity.
DE: 3902 Creep and deformation
DE: 3947 Surfaces and interfaces
DE: 5102 Acoustic properties
DE: 5112 Microstructure
DE: 8162 Rheology: mantle (8033)
SC: Tectonophysics [T]
MN: Fall Meeting 2005