Numerical Modeling of Cyclic Deformation in Bulk Metallic Glasses

Abstract

Abstract:In this paper, a systematic numerical simulation was performed to elucidate the damage mechanisms in bulk metallic glasses (BMGs) subjected to the tension-compression cyclic loading, and then the relation between fatigue life, applied strain, and cycling frequency was therefore presented. The free volume was selected as an internal state variable to depict the shear-band nucleation, growth, and coalescence with the help of free volume theory, which was incorporated into the ABAQUS code via a user material subroutine UMAT. Under cyclic loading, the shear banding initiation mainly stems from the microstructure inhomogeneity in BMGs and, further, the effect of applied strain amplitude and cycling frequency was discussed. The present simulations will shed some light on the fatigue damage mechanisms and fatigue life evaluation of BMG structures.

Collective nonaffine displacements in amorphous materials during large-amplitude oscillatory shear

“…On the other hand, it was shown that large strain cycles cause irreversible relaxations in the material and relocate the system to shallower energy minima, thus, leading to rejuvenation [40]. In the present study, the potential energy per particle in one representative sample is plotted where it was shown that after a certain number of cycles, the stress amplitude is reduced concomitantly with the initiation of a shear band across the sample [33,34]. We also comment that the transition from reversible dynamics at γ 0 = 0.07 to the plastic regime at γ 0 = 0.08 occurs at higher strain amplitudes than the critical value γ 0 = 0.06 reported in the previous MD study [10], where simulations were performed at the higher oscillation frequency ωτ = 0.02 and higher temperature T LJ = 0.1 ε/k B .…”

“…It was found that the amplitude of stress oscillations is reduced after the first several cycles, which is associated with the formation of a dominant shear band across the whole system [33,34]. In this process, the initiation of a shear band is preceded by an accumulation of shear transformation zones at the surface of the material.…”

“…Moreover, it was shown that higher cycling frequency leads to a larger number of cycles to failure [33,34]. Nevertheless, the microscopic details of the relaxation process in amorphous materials under various types of loading conditions remain not fully understood.…”

“…More recently, the fatigue mechanism in bulk metallic glasses subjected to tensioncompression cyclic loading was investigated using molecular dynamics (MD) simulations [33] and finite element modeling [34]. It was found that the amplitude of stress oscillations is reduced after the first several cycles, which is associated with the formation of a dominant shear band across the whole system [33,34].…”

Numerical Study on the Fatigue Limit of Metallic Glasses under Cyclic Tension-Compression Loading

“…Another work by MD simulation found that the localization of shear transformation zone obeys a power law with rate under tension-compression fatigue simulation [12]. By finite element method (FEM), Jiang [13] carried out a systematical simulation by classic free-volume theory to elucidate the damage mechanism in bulk metallic glasses. It was concluded that the fatigue endurance limit relied on different applied strain amplitude and cycling frequency.…”