The Physical Nature of Materials Strengths

The strength of a material is assessed most often by means of a tensile test. For a given material the fracture strength can be calculated by σF = Fmax/A0. For a bulk metallic glassy specimen, it often fails in a shear mode, and the shear fracture surface makes an angle of θT=56° with respect to the tension axis. Such shear fracture behavior has been widely observed in many metallic glasses. Consequently, this gives rise to some interesting and significant questions. Which is the real tensile strength of a metallic glass? Why do metallic glasses often fail neither along the maximum normal stress plane (θT =90°) nor along the maximum shear stress plane (θT = 45°) under tensile loading? What is the physical nature of the materials strength?