A polycrystalline iron sample (

PHYSICS · Multi-part · Fermi University Physics · Fluids & Continuum Physics · Solid continuum mechanics and complex fluids · Solid continuum mechanics and complex fluids

Bending, Ringing, Breaking and Flowing, Ch Dislocations and the onset of plastic flow

Problem

A polycrystalline iron sample (G=81 GPaG = 81\,\mathrm{GPa}, density ρ=7870 kg m−3\rho = 7870\,\mathrm{kg\,m^{-3}}, Burgers vector b=0.25 nmb = 0.25\,\mathrm{nm}) is being deformed plastically at a shear strain rate γ˙p=1×10−4 s−1\dot\gamma_p = 1\times10^{-4}\,\mathrm{s^{-1}}. The mobile dislocation density is ρm=5×1011 m−2\rho_m = 5\times10^{11}\,\mathrm{m^{-2}}. ((a)) Use the Orowan relation to find the average glide speed vv of the mobile dislocations. ((b)) Compare vv with the transverse (shear) wave speed cT=G/ρc_T = \sqrt{G/\rho}, and comment on what this comparison means for how fast a dislocation can in principle be driven.

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