Research Explores Mechanical Properties of Glasses

Research Explores Mechanical Properties of Glasses

Researchers from Osaka University simulated glassy colloidal solids to explore their mechanical and failure properties

Glasses are hard but amorphous solids and this structural disorder individual pieces of glass are technically out of equilibrium and unique. Therefore, properties of glass depend both on its chemical ingredients and the way it was cooled. The amorphous nature makes it challenging to describe glasses with a general model. Now, a team of researchers from Osaka University used simulations to connect the annealing of a glass with its mechanical response to pressure. The study that was published in the journal Science Advances on December 7, 2018 was focused on two main characteristics of solids: elasticity and plasticity.

An elastic solid returns to its original shape after pressure is released. However, plastics permanently retain their new shape.  The team modeled dense assembly of colloids that are a type of amorphous solid. Although the spheres do not represent real molecules, they help to determine whether such dense glasses are elastic. The team simulated the response of spheres to shear and normal strains. Supercomputers were used to map strain phase-diagrams of glass formers in order to analyze their rheology. The team found that each glass showed four basic trends. The glasses were perfectly elastic under small strains and at higher strains they became partially plastic as they fail to recover the original state when the deformation was partly lifted.

The glasses face either total failure by fracturing (yielding) to release stress or complete stop by jamming, when subjected to large strain. The region between yielding and jamming on the phase diagram described where the original glass remained stable. According to lead author Yuliang Jin, it is possible to understand the responses stable, partly stable, and unstable glasses and the size of the solid region and its stable sub-zone relies on how efficiently the glass was annealed. Efficiently annealed glasses have high chances of jamming under shear.