Accessing a broader range of energy states in metallic glasses by variable-amplitude oscillatory shear

Abstract

The influence of variable-amplitude loading on the potential energy and mechanical properties of amorphous materials is investigated using molecular dynamics simulations. We study a binary mixture that is either rapidly or slowly cooled across the glass transition temperature and then subjected to a sequence of shear cycles with strain amplitudes above and below the yielding strain. It was found that well annealed glasses can be rejuvenated by small-amplitude loading if the strain amplitude is occasionally increased above the critical value. By contrast, poorly annealed glasses are relocated to progressively lower energy states when subyield cycles are alternated with large-amplitude cycles that facilitate exploration of the potential energy landscape. The analysis of nonaffine displacements revealed that in both cases, the typical size of plastically rearranged domains varies depending on the strain amplitude and number of cycles, but remains smaller than the system size, thus preserving structural integrity of amorphous samples.

Yielding transition in stable glasses periodically deformed at finite temperature

“…For comparison, rapidly quenched KA glasses under cyclic shear with strain amplitudes below the critical value 0 ≈ 0.067 at = 0.01 ∕ and = 1.2 −3 settle at the lowest level ≈ −8.29 after one or two thousand cycles [39,45]. In addition, it was shown that periodic shear with 0 = 0.06 at 0.01 ∕ and 1.2 −3 does not lead to relaxation below ≈ −8.31 [49].…”

“…In the present study, we introduce a deformation protocol where the strain amplitude is gradually varied across a critical strain amplitude. It was shown previously that the critical strain amplitude for poorly annealed binary glasses is 0 ≈ 0.067 at = 0.01 ∕ and = 1.2 −3 and that better annealed glasses at the same conditions do not yield at 0 = 0.06 [39,45,49]. Therefore, the strain amplitude is set to vary linearly from 0 = 0.06 to 0.12 during 100 cycles, as follows:…”

“…Typically, a plastic event in a deformed disordered solid involves a group of atoms with relatively large nonaffine displacements. More recently, the collective behavior of atoms with large nonaffine displacements was investigated in disordered solids during elastostatic loading [61,62] as well as startup continuous [63][64][65][66][67][68][69] and oscillatory shear [28,34,35,39,42,43,45,47,49] deformation.…”

“…In the presence of thermal fluctuations, atoms do not follow exactly the same trajectories, and disordered solids might continue structural relaxation, or 'mechanical annealing', during thousands of subyield loading cycles [34,36,39]. Interestingly, it was recently shown that oscillatory shear deformation can lead to rejuvenation without formation of a shear band if the strain amplitude is only once in a while increased above a critical value [49]. On the other hand, the yielding transition is accompanied by strain localization, and the number of transient cycles depends on the initial glass state and strain amplitude [31,32,35,38,42,45], among other factors.…”

Mechanical annealing and memories in a disordered solid

“…Experiments and simulations that cyclically shear disordered solids have illuminated this mechanical history-dependence, aspects of which seem to be common to 2D and 3D disordered solids with many kinds of microscopic physics (5,(9)(10)(11)(12)(13)(14)(15)(16). In particular, athermal simulations show that when the material starts in a higher-energy configuration-as if quenched from a high-temperature liquid, without thermal annealing-and the amplitude of shear is below a critical value, this mechanical annealing lowers the overall energy of the structure (5,10,13,(17)(18)(19)(20)(21)(22)(23). Eventually, the material reaches a steady state in which the plastic rearrangements (Fig.…”