Rheology of Hard Glassy Materials

Abstract

Glassy solids may undergo a fluidization (yielding) transition upon deformation whereby the material starts to flow plastically. It has been a matter of debate whether this process is controlled by a specific time scale, from among different competing relaxation/kinetic processes. Here, two constitutive models of cage relaxation are examined within the microscopic model of nonaffine elasto-plasticity. One (widely used) constitutive model implies that the overall relaxation rate is dominated by the fastest between the structural ($\alpha$) relaxation rate and the shear-induced relaxation rate. A different model is formulated here which, instead, assumes that the slowest (global) relaxation process controls the overall relaxation. We show that the first model is not compatible with the existence of finite elastic shear modulus for quasistatic (low-frequency) deformation, while the second model is able to describe all key features of deformation of `hard' glassy solids, including the yielding transition, the nonaffine-to-affine plateau crossover, and the rate-stiffening of the modulus. The proposed framework provides an operational way to distinguish between `soft' glasses and `hard' glasses based on the shear-rate dependence of the structural relaxation time.

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Cited by in corpus (3)

• The Role of Collective Elasticity on Activated Structural Relaxation, Yielding and Steady State Flow in Hard Sphere Fluids and Colloidal Suspensions Under Strong Deformation
• Microscopic Activated Dynamics Theory of the Shear Rheology and Stress Overshoot in Ultra-Dense Glass-Forming Fluids and Colloidal Suspensions
• Nonequilibrium dynamical structure of a dilute suspension of active particles in a viscoelastic fluid