RheoMan: a five-year, ERC-funded (Advanced Grant), project to model the rheology of the Earth's mantle

Jul 23, 2015 Modeling creep Results

A new publication by F. Boioli et al. provides the first description beyond the Weertman model of the mechanisms underlying creep in olivine

Climb-assisted plastic deformation of olivine

 

At high temperatures dislocation climb, i.e. dislocation motion driven by absorption or emission of point defects, is an important recovery mechanism that can strongly influence the plastic behaviour. In this paper, we model creep resulting from the motion of dislocations involving thermally activated glide and climb.

 

 

By employing 2.5-dimensional dislocation dynamics simulations (for more detais on this technique, please see here) we show that the interplay between glide and climb leads to steady state deformation conditions. The climb mechanism, in fact, allows dislocations to bypass obstacles and to move from a “quasi-equilibrium configuration” to another one, providing continually new mobile dislocations. At the steady-state the plastic strain ε increases linearly with time and the dislocation density ρ oscillates around a constant value as it is shown in the Figure above. Both the strain rate and the equilibrium dislocation density depend on the creep stress.

The resulting strain rates are shown in the figure below. In the investigated temperature and stress range (T=1400-1700 K, σ=10-120 MPa), a power law characterized by a constant stress exponent close to 3 and an activation enthalpy barrier of 5.1 eV (490 KJ/mol) is found.

In this paper, we also propose a semi-analytical model based on our dislocation dynamics simulations to describe the rheology of olivine at high temperatures. 

 

 

 

For more details, see the paper just published on-line:

F. Boioli, P. Carrez, and P. Cordier, B. Devincre, and M. Marquille,  Modeling the creep properties of olivine by 2.5-dimensional dislocation dynamics simulations,  Phys. Rev. B (2015), doi: 10.1103/PhysRevB.92.014115