Vibrational disorder and densification-induced homogenization of local elasticity in silicate glasses

We report the effect of structural compaction on the statistics of elastic disorder in a silicate glass, using heterogeneous elasticity theory with the coherent potential approximation (HET-CPA) and a log-normal distribution of the spatial fluctuations of the shear modulus. The object of our study, a soda lime magnesia silicate glass, is compacted by hot-compression up to 2 GPa (corresponding to a permanent densification of ~ 5%). Using THz vibrational spectroscopic data and bulk mechanical properties as inputs, HET-CPA evaluates the degree of disorder in terms of the length-scale of elastic fluctuations and the non-affine part of the shear modulus. Permanent densification decreases the extent of non-affine elasticity, resulting in a more homogeneous distribution of strain energy, while also decreasing the correlation length of elastic heterogeneity. Complementary 29Si magic angle spinning NMR spectroscopic data provide a short-range rationale for the effect of compression on glass structure in terms of a narrowing of the Si–O–Si bond-angle and the Si–Si distance.

Simulating Hypervelocity Impact and Material Failure in Glass

Simulating hypervelocity impact introduces a host of complexities due to inherent strain, pressure and strain rate sensitivities. Brittle materials, and glasses in particular, exhibit significant deviations from their respective quasi-static responses, displaying permanent densification, gradual softening, and significant variation in response depending on the degree of material damage. This work seeks to examine the evolution of material failure due to hypervelocity impact of a spherical steel projectile in to a soda-lime target plate over a range of impact velocities via the utilization of a scalable, explicit finite element code, Velodyne, and a high strain rate, brittle material model. It is shown that, by analyzing both the evolutionary instantaneous and accumulated failure behaviors, the resulting performance is profoundly effected by target/projectile geometries, as well as the complex behaviors observed with respect to shock propagation, reflection and interference.