"Butterfly Effect" in Shear-Banding Mediated Plasticity of Metallic Glasses

TL;DR

This paper reveals that shear banding in metallic glasses exhibits chaotic dynamics, which explains large plasticity fluctuations and sensitivity to initial conditions, akin to the butterfly effect in complex systems.

Contribution

It combines experimental and theoretical analysis to demonstrate chaotic shear-band dynamics and its impact on plasticity in metallic glasses, a novel insight into their deformation mechanisms.

Findings

Chaotic shear-band dynamics characterized by positive Lyapunov exponents.

Large plasticity fluctuations linked to chaotic shear-band behavior.

Tuning deformation parameters can reduce chaos and plasticity fluctuations.

Abstract

Metallic glasses response to the mechanical stress in a complex and inhomogeneous manner with plastic strain highly localized into nanoscale shear bands. Contrary to the well-defined deformation mechanism in crystalline solids, understanding the mechanical response mechanism and its intrinsic correlation with the macroscopical plasticity in metallic glasses remains long-standing issues. Through a combination of experimental and theoretical analysis, we showed that the shear banding process in metallic glasses exhibits complex chaotic dynamics, which manifests as the existence of a torus destroyed phase diagram, a positive Lyapunov exponent and a fractional Lyapunov dimension. We also demonstrated that the experimentally observed large plasticity fluctuation of metallic glasses tested at the same conditions can be interpreted from the chaotic shear-band dynamics, which could leads to an uncertainty on the appearance of the critical condition for runaway shear banding. Physically, the chaotic shear-band dynamics arises from the interplay between structural disordering and temperature rise within the shear band. By tuning the deformation parameters, the chaotic dynamics can be transformed to a periodic orbit state corresponding to a smaller plasticity fluctuation in metallic glasses. Our results suggest that the plastic flow of metallic glasses is a complex dynamic process, which is highly sensitive to initial conditions and reminiscent of the "butterfly effect" as observed in many complex dynamic systems.