[Paper Review] Yielding behavior of glasses under asymmetric cyclic deformation

Monoj Adhikari, Muhittin Mungan+1 more|arXiv (Cornell University)|Jan 17, 2022

Material Dynamics and Properties4 citations

TL;DR

This study investigates the yielding behavior of model glasses under asymmetric cyclic shear deformation, revealing a unique intermediate strain regime with high plasticity but no yielding in well-annealed glasses—contrasting sharply with symmetric shear. System size analysis shows this regime narrows with increasing size, leading to a reversal where well-annealed glasses yield at lower strain amplitudes than poorly annealed ones, a counterintuitive result explained by a mesostate model that captures the dynamics robustly.

ABSTRACT

We consider the yielding behaviour of a model glass subjected to asymmetric cyclic shear deformation, wherein the applied strain varies between 0 and a maximum value $γ_{ m max}$, and study its dependence on the degree of annealing of the glass and system size. The yielding behaviour of well annealed glasses (unlike poorly annealed glasses) display striking differences from the symmetric case, with the emergence of an intermediate strain regime with substantial plasticity but no yielding. The observed behaviour is satisfactorily captured by a recently proposed model. For larger system sizes, the intermediate strain regime narrows, leading to a remarkable reversal of yield strain with annealing.

Motivation & Objective

• To understand how asymmetric cyclic shear deformation affects yielding and plasticity in model glasses.
• To investigate the role of annealing degree and system size on yielding behavior under asymmetric deformation protocols.
• To identify whether the intermediate strain regime with high plasticity but no yielding is a generic feature of well-annealed glasses.
• To test the predictive power of a mesostate model in capturing the observed non-equilibrium dynamics.
• To determine the implications of finite-size effects on yield strain reversal in asymmetric shear.

Proposed method

• Simulating athermal quasistatic (AQS) shear on model glass systems with varying degrees of annealing and system sizes.
• Applying asymmetric cyclic shear protocols: 0 → γ₁_max → 0 → γ₁_max → ..., avoiding symmetric return to zero.
• Measuring minimum energy (E_min), plastic strain (γ_E_min), and maximum stress (σ_max) at steady state across strain amplitudes.
• Using a mesostate model with dynamic variables for energy and plastic strain, constrained within small ranges (δε = 0.05, δγ = 0.1) to match simulation data.
• Performing system size variation (N) to probe finite-size effects on the intermediate regime and yield transition.
• Comparing simulation results with model predictions to validate the model's ability to reproduce key features.

Experimental results

Research questions

• RQ1 How does asymmetric cyclic shear deformation alter the yielding behavior of well-annealed glasses compared to symmetric shear?
• RQ2 What is the nature and stability of the intermediate strain regime with high plasticity but no yielding in well-annealed glasses?
• RQ3 How does system size influence the emergence and width of the intermediate plastic regime?
• RQ4 Does the mesostate model accurately reproduce the non-monotonic stress and energy evolution observed in simulations?
• RQ5 What is the dependence of yield strain on annealing degree under asymmetric shear, and does it reverse compared to symmetric shear?

Key findings

• Well-annealed glasses under asymmetric cyclic shear exhibit a distinct intermediate strain regime (γ_peak < γ₁_max < γ_diff) with substantial plastic strain but no yielding, absent in symmetric shear.
• The intermediate regime narrows with increasing system size, suggesting it is a finite-size effect that vanishes in the thermodynamic limit.
• For large system sizes (N > 4000), the stress maximum occurs at γ_peak ≈ 0.1, and the stress drop becomes sharper with size.
• The yield strain γ_diff for well-annealed glasses is predicted to be smaller than for poorly annealed glasses under asymmetric shear, reversing the trend seen in symmetric shear.
• The mesostate model successfully reproduces the key features of the simulation data, including the evolution of energy and plastic strain, when constrained within small parameter ranges (δε = 0.05, δγ = 0.1).
• The model’s qualitative agreement with simulations indicates that plastic strain evolution is a critical, non-trivial factor in determining yielding behavior under asymmetric deformation.