Spiral fracture in metallic glasses and its correlation with failure criterion

We report the observation of spiral fracture of the metallic glass Zr41Ti14Cu12.5Ni10Be22.5 (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. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.