Shear Band Formation in Amorphous Materials under Oscillatory Shear Deformation

Dynamic screening by plasticity in amorphous solids

In recent work it was shown that elasticity theory can break down in amorphous solids subjected to nonuniform static loads. The elastic fields are screened by geometric dipoles; these stem from gradients of the quadrupole field associated with plastic responses. Here we study the dynamical responses induced by oscillatory loads. The required modification to classical elasticity is described. Exact solutions for the displacement field in circular geometry are presented, demonstrating that dipole screening results in essential departures from the expected predictions of classical elasticity theory. Numerical simulations are conducted to validate the theoretical predictions and to delineate their range of validity.

Effects of Si/Al ratio on structure, modulus of elasticity, and density in N-A-S-H geopolymer: a molecular dynamics simulation based on novel macromolecular model

The Si/Al ratio is of special importance in the structure of geopolymers and its change in structure causes geopolymers to show different properties. This study is based on the proposed macromolecular model taken from recent laboratory studies of the N-A-S-H geopolymer structure and is balanced in terms of electric charge with Na⁺ ions and aluminum atoms outside the structure. Macromolecular models were made with different ratios of Si/Al equal to 1, 2.16, and 3. Using classical molecular dynamics simulations, the results of Young's modulus, density, and radial distribution function of different Si/Al ratios were compared and the results were in good agreement with the available experimental data. This data is mandatory, please provide.

Bulk Metallic Glasses' Response to Oscillatory Stress Is Governed by the Topography of the Energy Landscape

When subjected to cyclic loading, bulk metallic glasses tend to exhibit fatigue-induced damage. Although fatigue is a key limitation of metallic glasses, its atomic origin remains elusive. Here, based on molecular dynamics simulations, we investigate the response of metallic glasses prepared with varying cooling rates to oscillatory stress. We find that fatigue manifests itself as an accumulation of residual strain, which results from some nonaffine displacement of the atoms. Such local reorganizations are promoted under a high cooling rate. Importantly, we demonstrate that the fatigue-induced dynamics of the atoms is encoded in the topography of the static energy landscape, i.e., before any load is applied.

Glass Stability Changes the Nature of Yielding under Oscillatory Shear

We perform molecular dynamics simulations to investigate the effect of a glass preparation on its yielding transition under oscillatory shear. We use swap Monte Carlo to investigate a broad range of glass stabilities from poorly annealed to highly stable systems. We observe a qualitative change in the nature of yielding, which evolves from ductile to brittle as glass stability increases. Our results disentangle the relative role of mechanical and thermal annealing on the mechanical properties of amorphous solids, which is relevant for various experimental situations from the rheology of soft materials to fatigue failure in metallic glasses.