Strain localization of non-crystalline solids.

摘要

Strain localization is an important deformation mode for many disordered materials, particularly for metallic glasses. However, the exact nature of the shear band instability in metallic glasses is not well understood. Using molecular dynamics, this dissertation detailed simulated mechanical tests, including uniaxial tension/compression, nanoindentation and simple shear, on four types of model metallic glasses. The degree of localization depends on the testing geometry, sample constraints, strain rates and, more significantly, on the extent of structural relaxation prior to mechanical testing. Shear bands form only in slowly quenched samples. In the most rapidly quenched samples higher strain rates lead to increased localization, while the more gradually quenched samples exhibit the opposite strain rate dependence. This observation suggests a deformation transition from homogeneous deformation to inhomogeneous deformation in the quasistatic limit. In three of the four model systems, we successfully elucidated the structural difference between samples with distinct thermal histories in terms of short range order (SRO). It was also found that the SRO is depleted in the shear band region which indicates an instability arising from structural softening. Moreover, the homogeneous to inhomogeneous transition in the mechanical properties coincides with the emergence of certain percolation of atoms with SRO.