Other
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmmr54a..03m&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #MR54A-03
Other
3909 Elasticity And Anelasticity, 5422 Ices, 5460 Physical Properties Of Materials, 6221 Europa, 8030 Microstructures
Scientific paper
The dissipation of tidal energy is considered a significant source of heating within many of the icy moons of Jupiter and Saturn. Our experimental study is designed to measure directly the dynamic responses of ice and other cryominerals in periodic loading and so identify and characterize microstructural parameters that influence the magnitude and mechanism(s) of anelastic dissipation. Laboratory-prepared polycrystalline ice and eutectic aggregates of ice/magnesium sulfate hydrate have been tested through a series of low- temperature/ambient-pressure, compression-compression cyclic loading experiments. Temperatures and frequencies were chosen to approach planetary conditions: T = 200 - 260K and f = 0.1 - 0.001 Hz, respectively. In addition to an applied mean stress ~1 MPa, the tests employed a sinusoidally varying stress sufficient to create elastic strains of magnitude ~5x10-6 to 3x10-5. Sample synthesis allowed control of grain-size. Fine-grained ice samples demonstrate a power law relationship between attenuation (QE-1) and frequency, i.e. QE-1 ∝ fm, with m approximately 0.3. Amplitude-dependent attenuation was observed in these samples, such that a 1x10-5 increase in strain amplitude resulted in an increase of QE-1 by 0.25. Measurements of the ice/magnesium sulfate hydrate samples show that the aggregates are more attenuating than pure ice at all frequencies: heterophase boundaries are so identified as significant sites for mechanical dissipation. Additionally, plastic extrusion was used to endow some samples with bulk fabric prior to dynamic testing, allowing exploration of the effect of strain history on attenuation. We will report the dependence of internal friction and dynamic Young's modulus on temperature, composition, strain amplitude, accumulated strain, and grain-size.
Berglund S. R.
Cooper Reid F.
Goldsby David L.
McCarthy Carolyn Cordwell
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