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Figures 5-8 show density and Si/Al coordination change during the compression-decompression cycle with and without a shear stress component using the two sets of parameters. In the original paper, the short-range interaction parameters for the Si-Li pair in the SHIK potential[1] were used by mistake for the Si-Na pair in the sodium aluminosilicate (NAS) glass. Si and Al coordination changes during the compression-decompression cycle in NAS without [(a) and (b)] and with shear [(c) and (d)] using the two sets of short-range interaction parameters. [Extracted from the article]

Experimental studies have shown that glass systems with high boron content exhibit superior crack resistance under sharp contact loading. However, the underlying mechanism is still not fully understood. In this context, we carried out classical molecular dynamics simulations on sodium aluminosilicate and sodium aluminoborate systems to investigate the effect of boron on the response of glass to nanoindentation. A rigid V-shaped indenter is used to indent the glass sample with a fixed loading rate, during which the indenter interacts with the glass via a repulsive force field. The indenter angle and tip radius are varied to study the effect of indenter sharpness, as what has been done in experiments. These simulated nanoindentation tests reveal how the stress/strain field and the glass structure evolve with deformation underneath the indenter. It was found that a large number of boron atoms in the plastic zone change from three- to fourfold coordination during the loading process, and most of them revert back to the threefold coordination state during the unloading process. Our study shows that this "reversible" boron coordination change plays a critical role in increasing the damage resistance of glass. [ABSTRACT FROM AUTHOR]

Under sharp contact loading, glass deforms elastically and then plastically via densification as well as shear flow. Stress build-up during loading, residual stress build-up after unloading, and possible ultimate cracking all depend sensitively on the competition and interplay between densification and shear flow. The crack resistance was shown in experimental studies to generally improve with the increasing contribution of densification in glasses where shear deformation plays a dominant role under indentation. In this work, the role of densification in deformation behaviors of model metallic glasses under sharp contact loading was studied by 3-D nanoindentation tests using indenters with different sharpness in classical molecular dynamics simulations. Starting from a model metallic glass that favors shear deformation, a Lennard-Jones potential was modified to describe model metallic glasses with different abilities of instantaneous densification under compression and permanent densification after decompression. Our studies show that model metallic glass with a higher densification ability under indentation has less stress build-up and less localized shear deformation during loading, as well as smaller residual stress build-up after unloading. However, our study indicates that both instantaneous and permanent densification need to be tuned for designing damage resistant glasses. [ABSTRACT FROM AUTHOR]

Temperature‐dependent viscosity is critical to decipher two profound questions in condensed matter physics, namely the glass transition and the relaxation of amorphous solids. However, direct measurement of viscosity over a large temperature range is extremely difficult. Here, using classical molecular dynamics (MD) simulations, we report a novel method to calculate the equilibrium viscosity of supercooled liquid both above and below the glass transition temperature (Tg) and to estimate the nonequilibrium viscosity of glass down to room temperature. Based on the shoving model, we derived an analytical formula showing that the shear viscosity in logarithmic scale changes linearly with the shear‐induced variation in shear modulus or potential energy of the glass‐forming system. The shear viscosity as a function of steady‐state potential energy of liquid under different shear strain rates can be directly calculated in MD simulations; together with its equilibrium potential energy, one can extrapolate the zero‐strain‐rate equilibrium viscosity. We verified the proposed model by reliably calculating equilibrium viscosity near Tg of four glass‐forming systems (Kob–Andersen system, silica, Cu45.5Zr45.5Al9, and silicon) with different fragilities. Furthermore, our model can estimate the nonequilibrium viscosity of glass below Tg; the upper‐bound nonequilibrium viscosity of amorphous silica and silicon at room temperature are calculated to be ~1032 and 1025 Pa·s, respectively. [ABSTRACT FROM AUTHOR]

Atomic level computer simulation has become indispensable in understanding the mechanical properties of glasses, among other properties. However, the majority of model glasses are more ductile than their intended experimental counterparts, partially reflected by the overestimation of the Poisson's ratio. We have previously introduced an effective force field tuning method of imposing an additional energy penalty term to embrittle a binary Lennard-Jones glass. Here, we improved this method by varying the applied range of the energy penalty. The new method stabilizes the model glass even for high energy penalty values. Furthermore, unlike the old method, there is no unintended reduction in density for brittle glasses. Uniaxial tension tests were conducted to show the ductile-to-brittle transition as the energy penalty increases in strength. Crack propagation simulation was also conducted to demonstrate the efficacy of studying brittle fracture using the model glass. [ABSTRACT FROM AUTHOR]