# Origin of the Bauschinger Effect in Amorphous Solids

## TL;DR

This paper investigates the structural origins of the Bauschinger effect in amorphous solids by analyzing local plastic thresholds and demonstrating how unloading induces reverse plasticity, leading to the effect's characteristic material polarization.

## Contribution

It introduces a numerical method to analyze local residual strengths and models the plastic response, revealing the structural basis of the Bauschinger effect in amorphous materials.

## Key findings

- Plastic deformation induces material polarization with forward-backward asymmetry.
- Unloading causes reverse plasticity and softening, reversing the polarization.
- The proposed scenario explains the ubiquity of the Bauschinger effect in amorphous solids.

## Abstract

We study the structural origin of the Bauschinger effect by accessing numerically the local plastic thresholds in the steady state flow of a two-dimensional model glass under athermal quasistatic deformation. More specifically, we compute the local residual strength, $\Delta\tau^{c}$, for arbitrary loading orientations and find that plastic deformation generically induces material polarization, i.e., a forward-backward asymmetry in the $\Delta\tau^{c}$ distribution. In steady plastic flow, local packings are on average closer to forward (rather than backward) instabilities, due to the stress-induced bias of barriers. However, presumably due to mechanical noise, a significant fraction of zones lie close to reverse (backward) yielding, as the distribution of $\Delta\tau^{c}$ for reverse shearing extends quasilinearly down to zero local residual strength. By constructing an elementary model of the early plastic response, we then show that unloading causes reverse plasticity of a growing amplitude, i.e., reverse softening, while it shifts away forward-yielding barriers. This result in an inversion of polarization in the low-$\Delta\tau^{c}$ region and, consequently, in the Bauschinger effect. This scenario is quite generic, which explains the pervasiveness of the effect.