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arXiv · 1702.00620

Atomic-scale origin of dynamic viscoelastic response and creep in disordered solids

Rico Milkus·Alessio Zaccone
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Abstract

Viscoelasticity has been described since the time of Maxwell as an interpolation of purely viscous and purely elastic response, but its microscopic atomic-level mechanism in solids has remained elusive. We studied three model disordered solids: a random lattice, the bond-depleted fcc lattice, and the fcc lattice with vacancies. Within the harmonic approximation for central-force lattices, we applied sum-rules for viscoelastic response derived on the basis of non-affine atomic motions. The latter motions are a direct result of local structural disorder, and in particular, of the lack of inversion-symmetry in disordered lattices. By defining a suitable quantitative and general atomic-level measure of nonaffinity and inversion-symmetry, we show that the viscoelastic responses of all three systems collapse onto a master curve upon normalizing by the overall strength of inversion-symmetry breaking in each system. Close to the isostatic point for central-force lattices, power-law creep $G(t)\sim t^{-1/2}$ emerges as a consequence of the interplay between soft vibrational modes and non-affine dynamics, and various analytical scalings, supported by numerical calculations, are predicted by the theory.

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Rico Milkus, Alessio Zaccone. 2017-02-02. Atomic-scale origin of dynamic viscoelastic response and creep in disordered solids. https://doi.org/10.1103/physreve.95.023001

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