Alternating Shear Orientation During Cyclic Loading Facilitates Yielding in Amorphous Materials
- PDF / 5,837,902 Bytes
- 8 Pages / 593.972 x 792 pts Page_size
- 73 Downloads / 138 Views
JMEPEG https://doi.org/10.1007/s11665-020-05138-5
Alternating Shear Orientation During Cyclic Loading Facilitates Yielding in Amorphous Materials Nikolai V. Priezjev (Submitted April 8, 2020; in revised form July 12, 2020; Accepted September 5, 2020) The influence of alternating shear orientation and strain amplitude of cyclic loading on yielding in amorphous solids is investigated using molecular dynamics simulations. The model glass is represented via a binary mixture that was rapidly cooled well below the glass transition temperature and then subjected to oscillatory shear deformation. It was shown that periodic loading at strain amplitudes above the critical value first induces structural relaxation via irreversible displacements of clusters of atoms during a number of transient cycles, followed by an increase in potential energy due to the formation of a system-spanning shear band. Upon approaching the critical strain amplitude from above, the number of transient cycles required to reach the yielding transition increases. Interestingly, it was found that when the shear orientation is periodically alternated in two or three dimensions, the number of transient cycles is reduced but the critical strain amplitude remains the same as in the case of periodic shear along a single plane. After the yielding transition, the material outside the shear band continues strain-induced relaxation, except when the shear orientation is alternated in three dimensions and the glass is deformed along the shear band with the imposed strain amplitude every third cycle. Keywords
metallic glasses, molecular dynamics simulations, oscillatory deformation, yielding transition
1. Introduction Understanding the relationship between the local atomic structure of amorphous alloys and their mechanical and physical properties is important for various structural, biomedical and environmental applications (Ref 1-3). It is well accepted that in contrast to crystalline materials, where plastic deformation is governed by motion of topological line defects, or dislocations, the elementary plastic event in amorphous materials involves a collective rearrangement of small group of atoms, or a shear transformation (Ref 4, 5). The lack of crystalline order in metallic glasses results in relatively highyield strength, and, at the same time, if brought to a relaxed state, glasses can fail via sudden formation of shear bands where strain becomes localized along narrow layers (Ref 6, 7). On the other hand, metallic glasses can be made more ductile if they are mechanically or thermally rejuvenated or, alternatively, formed by rapid cooling from the liquid state. In the past, a number of thermomechanical processing methods, such as cold rolling, high-pressure torsion, thermal cycling, elastostatic loading and irradiation, were developed to rejuvenate glasses and improve plasticity (Ref 8). Despite recent advances, however, the structural relaxation and critical behavior in metallic glasses during time-periodic mechanical deformation are yet to be fully underst
Data Loading...
