Book contents
- Frontmatter
- Contents
- Preface
- Part I General background
- Part II Materials science of deformation
- 4 Elasticity
- 5 Crystalline defects
- 6 Experimental techniques for study of plastic deformation
- 7 Brittle deformation, brittle–plastic and brittle–ductile transition
- 8 Diffusion and diffusional creep
- 9 Dislocation creep
- 10 Effects of pressure and water
- 11 Physical mechanisms of seismic wave attenuation
- 12 Deformation of multi-phase materials
- 13 Grain size
- 14 Lattice-preferred orientation
- 15 Effects of phase transformations
- 16 Stability and localization of deformation
- Part III Geological and geophysical applications
- References
- Materials index
- Subject index
- Plate section
10 - Effects of pressure and water
Published online by Cambridge University Press: 05 June 2012
- Frontmatter
- Contents
- Preface
- Part I General background
- Part II Materials science of deformation
- 4 Elasticity
- 5 Crystalline defects
- 6 Experimental techniques for study of plastic deformation
- 7 Brittle deformation, brittle–plastic and brittle–ductile transition
- 8 Diffusion and diffusional creep
- 9 Dislocation creep
- 10 Effects of pressure and water
- 11 Physical mechanisms of seismic wave attenuation
- 12 Deformation of multi-phase materials
- 13 Grain size
- 14 Lattice-preferred orientation
- 15 Effects of phase transformations
- 16 Stability and localization of deformation
- Part III Geological and geophysical applications
- References
- Materials index
- Subject index
- Plate section
Summary
Pressure has important effects on plastic flow. Pressure affects the rate of plastic flow through two distinct mechanisms. First, the height of the potential barrier for atomic motion changes with pressure, which usually makes plastic flow more difficult at higher pressures. This effect is mainly characterized by a parameter called activation volume. Experimental observations and theoretical models of activation volume are summarized including the pressure dependence of activation volume. For a constant stress, the rate of deformation changes with pressure by as much as ten orders of magnitude in Earth's interior. Second, pressure modifies the chemical environment particularly the fugacity of water that controls the concentration of point defects and changes the rate of plastic deformation. The fugacity of water becomes higher at higher pressures, which enhances the rate of plastic deformation by several orders of magnitude. Experimental observations and theoretical models of effects of pressure and water on plastic deformation are reviewed including empirical correlations such as the homologous temperature scaling and some atomistic models of defects.
Key words activation volume, homologous temperature, Keyes model, water fugacity, hydrogen-related defects, FT–IR spectroscopy.
Introduction
It is often argued that the strength of a rock in a brittle regime increases strongly with pressure, but the strength in the ductile (plastic flow) regime is relatively insensitive to pressure. This is misleading, however, and in fact, the effects of pressure on plastic deformation can be large and complicated under the conditions of Earth's deep interior.
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- Deformation of Earth MaterialsAn Introduction to the Rheology of Solid Earth, pp. 168 - 198Publisher: Cambridge University PressPrint publication year: 2008
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