Elementary plastic events in amorphous silica.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Computational Chemistry

Background:

• Amorphous materials, like silica glass, exhibit plastic instabilities.
• Current models often use simplified binary mixtures, neglecting real molecular interactions and bonding.
• Understanding atomic-scale events is crucial for accurate plasticity models.

Purpose of the Study:

• To investigate atomic-scale plastic instabilities in a realistic silica glass model.
• To identify and characterize distinct elementary plastic events.
• To correlate these events with mechanical properties and predict structural failure.

Main Methods:

• Utilized a three-dimensional molecular dynamics model of silica glass.
• Applied quasistatic shear to simulate material deformation.
• Analyzed the Hessian matrix and its eigenvalues/eigenvectors to identify critical events.

Main Results:

• Identified two types of plastic events: atomic rearrangement and bond breaking.
• Observed a drop in the lowest nonzero Hessian eigenvalue preceding plastic events.
• Found strong correlation between eigenvectors and nonaffine displacements, predicting failure loci.
• Noted Eshelby-like quadrupolar structures in both failure modes.

Conclusions:

• Clarified the nature of atomic-scale plastic instabilities in silica glasses.
• Demonstrated the predictive power of Hessian analysis for plastic events, including bond breaking.
• Provided insights for developing more accurate mesoscale models of amorphous plasticity.