6.4 summaries the fracture angle in various BMGs [21−29]. It is observable that the fracture angle is generally in the range of 39−44° for compression and 50−60° for tension. However, according to the classical von Mises or Tresca criterion, this angle would be expected to lie at 45° to the compression axis. Thus both criterions cannot satisfactorily explain the fracture behaviour of metallic glasses, which consider only the shear stresses in polycrystalline metals. Donvan [30] recently demonstrated that yielding/fracture follows the Mohr-Coulomb criterion by investigating a Pd40Ni40P20 metallic under different loading modes. He suggested that shear fracture of BMGs depends not only on the shear stress but also on the stress normal to the shear plane. The general form of the criterion can be described as with the effective shear fracture stress, and the shear and normal stresses on the shear τy τ0 σ0 plane, respectively, and a empirical constant. Using the mechanical date of =1552 MPa α σf and =44°, and can be calculated by following expression: θ τ0 σ0 The fracture angles and were to be closely related to the constant by [31] θc θt α Thus the constant is determined to be 0.035. By substituting and into Eq. α τ0, σ0 α (6.5), the effective shear fracture stress for the current Zr-based BMG can be obtained τy
6.4 summaries the fracture angle in various BMGs [21−29]. It is observable that the fracture angle is generally in the range of 39−44° for compression and 50−60° for tension. However, according to the classical von Mises or Tresca criterion, this angle would be expected to lie at 45° to the compression axis. Thus both criterions cannot satisfactorily explain the fracture behaviour of metallic glasses, which consider only the shear stresses in polycrystalline metals. Donvan [30] recently demonstrated that yielding/fracture follows the Mohr-Coulomb criterion by investigating a Pd40Ni40P20 metallic under different loading modes. He suggested that shear fracture of BMGs depends not only on the shear stress but also on the stress normal to the shear plane. The general form of the criterion can be described as with τy the effective shear fracture stress, τ0 and σ0 the shear and normal stresses on the shear plane, respectively, and α a empirical constant. Using the mechanical date of σf =1552 MPa and θ =44°, τ0 and σ0 can be calculated by following expression: The fracture angles θc and θt were to be closely related to the constant α by [31] Thus the constant α is determined to be 0.035. By substituting τ0, σ0 and α into Eq. (6.5), the effective shear fracture stress τy for the current Zr-based BMG can be obtained
Shuang%20thesis.docx