On the Olivine-Spinel Transformation as a Rheometer

Tuesday, March 19, 2002 - 9:10am - 10:10am
Keller 3-180
Stephen Morris (University of California, Berkeley)
Kubo et al (Science, 281, 85-87, 1998) show experimentally that during the growth of a rim of new spinel phase on a grain of olivine, the rheology of the spinel can control the transformation rate. In work in press (Morris, J. Mech. Phys. Solids, 2002), I show that those data can be fitted by a model coupling interface kinetics to the viscoelastic creep required to accomodate the transformation--induced volume change. Because those data cover a limited range of strain rate, they can be fitted by a model in which the creep rate is taken as proportional to deviatoric stress. My theory allows the effective viscosiy of the spinel to be inferred for certain of Kubo's experiments. The viscosity so inferred is, of course, valid only for a limited range of strain rate.

In this talk, I will review the study in press, and then describe analysis in progress which incorporates creep by the actual mechanism of low temperature plasticity occurring in the experiments. The purpose of the new work is to determine the zero temperature yield stress for spinel, and also to predict the variation of transformation-rate with excess pressure.