Soft spots of net negative topological charge directly cause the plasticity of 3D glasses
arxiv(2024)
摘要
The deformation mechanism in amorphous solids subjected to external shear
remains poorly understood because of the absence of well-defined topological
defects mediating the plastic deformation. The notion of soft spots has emerged
as a useful tool to characterize the onset of irreversible rearrangements and
plastic flow, but these entities are not well-defined in terms of geometry and
topology. In this study, we unveil the phenomenology of recently discovered,
well-defined topological defects governing the microscopic mechanical and
yielding behavior of a model 3D glass under shear deformation. We identify the
existence of vortex-like and anti-vortex-like topological defects within the 3D
non-affine displacement field. The number density of these defects exhibits a
significant (inverse) correlation with the plastic events, with defect
proliferation-annihilation cycles matching the alternation of elastic-like
segments and catastrophic plastic drops, respectively. Furthermore, we observe
collective annihilation of these point-like defects via plastic events, with
large local topological charge fluctuations in the vicinity of regions that
feature strong non-affine displacements. We unveil that plastic yielding is
driven by very few, but very large, clusters of net negative topological
charge, the massive annihilation of which triggers the onset of plastic flow.
These findings suggest a geometric and topological characterization of soft
spots and pave the way for the mechanistic understanding of topological defects
as mediators of plastic deformation in glassy materials.
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