Spiral fracture in metallic glasses and its correlation with failure criterion

Abstract

a b s t r a c tWe report the observation of spiral fracture of the metallic glass Zr 41 Ti 14 Cu 12.5 Ni 10 Be 22.5 (at.%) subjected to both shear and normal stresses. The spiral angle (that between the spiral line and the loading axis) increases as we gradually change the normal stress from tensile (positive) to compressive (negative). The spiral nature of the fractured surface leads to a left-handed helix fractography pattern in tension, and a right-handed helix in compression. The Mohr-Coulomb type of failure is essential for the unique spiral fracture. The use of spiral angles resulted from torsion-tension experiments provide another novel experimental strategy to examine the failure criterion as well as stress state dependence of deformation mechanisms which lead to failure in metallic glasses.

Unusually thick shear-softening surface of micrometer-size metallic glasses

“…Since the loading mode is pure shear, the fracture along~45 inclined to the axial direction in the torsion in fact corresponds to the fracture vertical to the loading axis in tension, suggesting a brittle fracture behavior dominated by the Mode I crack, similar to what occurs in ceramics. 41 The fracture angles of the MGWs, in contrast, are much smaller than that of the bulk MG rod and decrease with decreasing diameters, as shown in Figures 5B-5D. The fracture plane for the 52-mm-diameter MGW is nearly flat (Figure 5D), which corresponds to the Mode III crack and is the same as the torsion fracture of ductile alloys.…”

Deformation map of metallic glass: Normal stress effect

“…Given the new discovery, more detailed deformation maps of MGs have been developed individually by Lu et al [4], Schuh et al [1] and Sun et al [15]. Nevertheless, the previous researchers usually investigated the deformation maps using one testing method (e.g., compression, tension or nanoindentation) [1,4,[11][12][13][14][15], and few studies [16][17][18] focused on the comparison of deformation mode features under different loading modes, as well as the normal stress effect on deformation map of MG, especially at high temperatures.…”

Macroscopic tensile plasticity of Zr-based bulk metallic glass with surface screw thread shaped structure

“…This STS structure induced twisted stress field is analogous to the stress field under torsion loading and the torsion stress is actually the restricted stress field. Under the twisted stress field, multiple SBs formation could be easily promoted, the main SB propagation could be stabilized, and then contributes to the occurrence of macroscopic plastic deformation [25,26].…”