Physics
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.p42b..04m&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #P42B-04
Physics
5422 Ices, 5460 Physical Properties Of Materials, 6221 Europa, 8030 Microstructures, 8160 Rheology: General (1236, 8032)
Scientific paper
The presence of non-ice material (e.g. salt-hydrate) on the surface of icy satellites requires that we consider the influence of a second phase on the mechanical properties of ice. We are investigating experimentally the flow-strength and relaxation response (attenuation) of two-phase aggregates of magnesium sulfate hydrate and ice-I through compression creep tests (T = 240-250K; σ = 0.9-9.0 MPa) in a 1-atm, dead-weight, deformation apparatus modified for cryogenic use. All samples in our study crystallize from a homogeneous liquid solution that produces a classical eutectic microstructure. A misting and hot-pressing technique allows us to control grain size, or more accurately, colony size, in the samples. The steady-state (secondary) creep response of the ice/hydrate aggregate reveals that it has a viscosity that is at least an order of magnitude greater than that of pure polycrystalline ice at the same stress and temperature in what appears to be a dislocation creep regime. Since heterophase boundaries are found to be an effective barrier to dislocation motion, we attribute the increase in strength to the high volume of incoherent interfaces that the eutectic microstructure provides. We are also examining the transient (primary) creep in the strain response; this relaxation is an indication of the dissipative quality of the material from which we may begin to understand how mechanical energy (such as that from tidal loading) could be absorbed (dissipated) in the crust as heat. Information gleaned from these experiments can help constrain models of crustal thickness and surface dynamics on Europa.
Cooper Reid F.
Durham William B.
Goldsby David L.
Kirby Stephen H.
McCarthy Carolyn Cordwell
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