Vibration Modes and Characteristic Length Scales in Amorphous Materials

Abstract

The numerical study of the mechanical responses of amorphous materials at the nanometer scale shows characteristic length scales that are larger than the intrinsic length of the microstructure. In this article, we review the different scales appearing upon athermal elastoplastic mechanical load and we relate it to a detailed study of the vibrational response. We compare different materials with different microstructures and different bond directionality (from Lennard-Jones model materials to amorphous silicon and silicate glasses). This work suggests experimental measurements that could help to understand and, if possible, to predict plastic deformation in glasses.

Propagative and diffusive regimes of acoustic damping in bulk amorphous material

“…2(a)) becomes definitely dominant at higher frequencies. This very small intrinsic length dominates the correlation function in the studied model of amorphous silicon at all frequencies above the Ioffe-Regel criterion, as already discussed in [6].…”

Correlations in the shear flow of athermal amorphous solids: a principal component analysis

“…Typical nonaffine displacements fields are shown in Figure 1 for both regimes. As reported in many previous works [12,9,15,11], localized large displacements with distinct quadrupolar symmetry are associated with the plastic regime, whereas the elastic regime is characterized by extended vortices.…”

“…The displacement field exhibits strong rotational character, and their correlations range over a length scale of 20-30 particle diameters and reflect the scale above which the material can be viewed as a homogeneous elastic medium [10]. The displacements from individual plastic shear transformations, however, are far more localized and can be thought of as forming at the intersection between (large) vortices [11]. When displacements are accumulated over larger strains, the plastic activity focuses particle motion along slip lines or micro shear bands [12,13,14].…”

Detailed analysis of plastic shear in the Raman spectra of SiO2 glass

“…Oxygen motion appears thus very sensitive to the frequency in the intermediate frequency range 700-900 cm −1 . After a strong decay of the Participation Ratio corresponding to localization processes [48], the P.R. increases again between 1000 and 1200 cm −1 .…”