02.06.21 RU Seminar - Jan Griesser "Vibrational lifetimes and viscoelastic dissipation in ultrastable glasses"

Elastic materials respond with a deformation to external load and return to their original shape when the load vanishes. In ideal elastic solids, the energy stored in the deformation is fully recovered as the material returns to its original shape. Real solids always dissipate energy proportional to the rate of change of the deformation. Such viscoelastic effects are strong for soft polymeric (rubbery) materials, but they are also present in hard materials such as glasses or even crystals [1,2]. In glasses, energy dissipation during elastic deformation can be traced back to non-affine displacements [3].

 

Here we use molecular dynamics simulations to study the dissipated power during cyclic deformation in glasses of varying stability. On a fundamental level, energy dissipation results from the excitation and decay of the vibrational modes of the solid. We model these vibrational modes as damped harmonic oscillators driven by the non-affine displacements field. Dissipation of individual modes emerges through mode-mode coupling and is characterized by the modes' lifetimes, which we obtain from the decay of energy autocorrelation functions [4]. Given non-affine displacements, lifetimes, and the vibrational density of states, we can solve the corresponding equations of motion to yield a parameter-free expression of viscoelastic dissipation as a function of external driving frequency in glasses. This expression allows us to predict the dissipated power as a function of glass morphology and temperature.

 

[1] J. D. Ferry, John Wiley \& Sons 1980

[2] Y. Hai-Bin and K. Samwer,  Phys. Rev. B 90.14 (2014)

[3] A.  Lemaitre  and  C.  Maloney, J. Stat. Phys. 415 (2006)

[4] A. JH. McGaughey and M. Kaviany, Phys. Rev. B 69.9 (2004)