The local stress state of a running shear band in amorphous solids
- PDF / 609,213 Bytes
- 9 Pages / 584.957 x 782.986 pts Page_size
- 68 Downloads / 175 Views
In molecular dynamics simulations, the local stress state in the shear band is examined in six different model metallic glasses and one amorphous Si system (also has been perceived as a metallic glass analog) under different loading conditions. For all but the FeP and the amorphous Si systems, the running shear band (RSB) exhibits a liquid-like hydrostatic plus shear stress state. Our results suggest that the liquid feature of a RSB is not due to temperature rise or plastic confinement but due to the disorder driven by flow, which can be offset by strong directionality in bonding, phase segregation, or aging. The knowledge of the liquid-like stress state can be conveniently utilized in experiments to infer the local stress state of the RSB from the global tensile stress for metallic glasses. I. INTRODUCTION
Similar to dislocations in crystalline materials, shear bands are the major plasticity carriers in metallic glasses which control the yielding, even fracture.1,2 Despite the vital importance, the nature of shear banding in metallic glasses has not been completely understood. The shear banding process can be separated into the initiation stage (the formation of across-the-sample shear band) and the subsequent gliding stage (the shear slip along the shear band).3,4 The initiation of a shear band has long been ascribed to work softening or shear thinning.5 Structural disorder inside the shear band was predicted to be the origin of the work softening, instead of thermal softening.5 This notion was supported by experiments6–9 and atomic simulations.10,11 Specifically, the structural disorder has been characterized as the break down of the local stable clusters or the short-range order3,10,12,13 in atomic simulations. During the subsequent gliding stage, the shear band endures high local shear strain under extremely high rate, which can lead to temperature rise,4,8 void formation,14–18 and final fracture.2,19 The transient dynamics shear band experiences also depend on the material properties and the machine stiffness.4,20,21 Multiple remarkable scaling behaviors discovered in the flow state22–24 indicate that the shear banding can be considered as a mechanically driven glass-to-liquid transition. It should be also noted that this liquid-like state of the shear band appears to be weakly dependent on the quenching history of the glass.11,25 Despite the above recent advances in understanding the shear band, the local stress state in the running shear
Contributing Editor: Franz Faupel a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2015.141 J. Mater. Res., Vol. 30, No. 12, Jun 28, 2015
band (RSB), a shear band that is in the flow state, has not been clearly understood.2 Experimentally, it is generally difficult to examine the local stress state in the RSB in experiments due to the limited spatio-temporal resolution.2,26 Among the existing theoretical or simulation studies,4,27 it is commonly assumed that the hydrostatic stress and shear stress in the RSB are different from the rest of the
Data Loading...
