Nanoindentation-induced evolution of atomic-level properties in silicate glass: Insights from molecular dynamics simulations

Indentation has been widely used for investigating the mechanical behavior of glasses. However, how the various microscopic properties (such as atomic structure and mechanics) of glass evolve from the immediate contact with the indenter to the far-field regions, and how these observables are correlated to each other remain largely unknown. Here, using large-scale molecular dynamics simulations, we investigate the response of a prototypical sodium silicate glass under shape contact load up to an indentation depth of 25 nm. Both the short- and intermediate-range structures are found to exhibit notable changes below the indent, indicating that indentation deformation induces a more disordered and heterogeneous network structure. In addition, we find that the indentation-induced changes of local properties all exhibit an exponential decaying behavior with increasing distance from the indent. Comparison of the characteristic decay lengths of these local properties indicates that the structural origins of shear flow and densification are the changes of the network modifier's coordination environment and the inter-tetrahedral connection, respectively. The decay of densification is considerably slower than that of shear strain, implying that the former might contribute more to the deformation at the far-field regions. Our findings not only contribute to an atomistic understanding of the indentation response of silicate glasses but also pave the way towards rational design of damage-resistant glassy materials.