Pressure and strain dependence of the strength of sintered polycrystalline Mg sub(2)SiO sub(4) ringwoodite

Differential stresses in a cylindrical rock of polycrystalline Mg sub(2)SiO sub(4) ringwoodite were measured at room temperature with pressures up to 10 GPa, axial strains in excess of 20%, and strain rates between 5 10 super(-5) and 4 10 super(-6) s super(-1), using the deformation-DIA coupled with monochromatic X-rays. The sample exhibited ductile behavior in axial shortening-lengthening cycles with reproducible hysteresis loops, yielding multiple well-defined stress-strain curves. Significant strain hardening was observed beyond the yield point, which occurs at axial strains around 1.5%. Large discrepancies in strength data on ringwoodite reported in previous studies, where no strain information could be obtained, can be reconciled by the strain hardening behavior. Above 8% axial strain, sample stresses reach saturation and the deformation reaches steady state, during which process the ultimate strength increases with hydrostatic pressure but are insensitive to strain rate, suggesting that the sample deforms in low-temperature plasticity regime.