![]() ![]() This means that the magnitude of the stress cannot exceed the yield strength of a material, and the time scale of the stress cannot approach the relaxation time of the material. Materials only behave elastically when the relative arrangement along the axis being considered of material components (e.g. Elastic Įlastic deformation is always reversible, which means that if the stress field associated with elastic deformation is removed, the material will return to its previous state. In the Earth, the compression of rocks with depth is significant, and an equation of state is needed to calculate changes in density of rock even when it is of uniform composition. In a body like the Moon, the density is almost constant, so a pressure profile is readily calculated. The pressure on rock depends only on the weight of the rock above, and this depends on gravity and the density of the rock. Since, over long periods, rocks readily deform under pressure, the Earth is in hydrostatic equilibrium to a good approximation. If there is no shear, the fluid is in hydrostatic equilibrium. Pressure is the part of stress that changes the volume of a solid shear stress changes the shape. Stress is defined as the average force per unit area exerted on each part of the rock. Rocks and other geological materials experience strain according to three distinct modes, elastic, plastic, and brittle depending on the properties of the material and the magnitude of the stress field. For a more rigorous treatment, see Deformation (mechanics). This article is about deformation in geology. Finding and understanding the driving mechanisms behind plate tectonics.Observing surface deformation and relaxation due to ice sheets and post-glacial rebound, and making related conjectures about the viscosity of the mantle.Predicting patterns of continental accretion and breakup of continents and supercontinents.Modeling brittle and ductile deformation of geologic materials.Work performed by geodynamicists may include: Įxperts in geodynamics commonly use data from geodetic GPS, InSAR, and seismology, along with numerical models, to study the evolution of the Earth's lithosphere, mantle and core. When working with geological timescales and lengths, it is convenient to use the continuous medium approximation and equilibrium stress fields to consider the average response to average stress. Rocks are structurally and compositionally heterogeneous and are subjected to variable stresses, so it is common to see different types of deformation in close spatial and temporal proximity. This deformation may be brittle, elastic, or plastic, depending on the magnitude of the stress and the material's physical properties, especially the stress relaxation time scale. In the Earth's interior, movement happens when rocks melt or deform and flow in response to a stress field. 2, Gauthier-Villars, Paris (Reproduction Bibliothe ́que Nationale de France, 1995).Geodynamics is generally concerned with processes that move materials throughout the Earth. (1903), The ́orie analytique de la chaleur, Vol. May (2007), Incompressible viscous formulations for deformation and yielding of the lithosphere, Geological Society London Special Publications, 282(1), 457–472, doi:10.1144/SP282.19. Doin (1997), A comparison of methods for the modeling of thermochemical convection, J. Muhlhaus (2003), A Lagrangian integration point finite element method for large deformation modeling of viscoelastic geomaterials, Journal of Computational Physics, 184(2), 476–497, doi:10.1016/S0021-9991(02)00031-1. Muhlhaus (2002), Mantle convection modeling with viscoelastic/brittle lithosphere: Numerical methodology and plate tectonic modeling, Pure And Applied Geophysics, 159(10), 2335–2356, doi:10.1007/s0002-3. The orientation tensor and the yield stress are usually modelled to include a simple damage evolution that relates to the work expended in deforming the material at yield. Typically, \(\eta\) varies by several tens of orders of magnitude over the typical temperature ranges expected between the Earth’s surface and interior. \(\Lambda\) is a structural tensor that represents the orientation of the plastic deformation relative to the applied stress and \(\lambda\) is a scalar multiplier that is computed to satisfy the stress conditions at yield. Where \(\mu\) is the elastic shear modulus and \(\eta\) is the shear viscosity (both of which may vary with temperature and composition). ![]()
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