Deciphering the α relaxation and the anelastic-to-plastic transition in the deep glassy state

In contrast to their conventional crystalline counterparts, amorphous solids exhibit diverse dynamic relaxation mechanisms under external stimuli. The challenge to understanding their behavior lies in unifying microscopic dynamics, relaxation, and macroscopic deformation. This study establishes a potential link by quantifying the characteristic time of the anelastic-to-plastic transition through dynamic mechanical relaxation and stress relaxation tests across a wide temperature range in both the supercooled liquid and the glassy state. It is found that the stress relaxation time in the glassy solids follows an Arrhenius relationship, aligning with the main α relaxation time, and unveils a finding: α relaxation continues to govern deformation even below the glass transition, challenging previous assumptions of the role of secondary β relaxation. A hierarchically constrained atomic dynamics model rationalizes the temperature dependence of α relaxation and the transition from β to α relaxation, also providing evidence that the stretched exponent in the Kohlrausch-Williams-Watts equation can serve as an order parameter. This work highlights the role of α relaxation in the glassy state and contributes to elucidating the potential correlation between relaxation and deformation in amorphous materials.