Zhe-Feng Zhang

Professor
Former Vice Director
Institute of Metal Research, Chinese Academy of Sciences, China

Biography: Prof. Zhe Feng Zhang is now working at Institute of Metal Research, Chinese Academy of Sciences, Shenyang, China. He received his Ph. D in 1998 and became full professor in 2004. He had visited Industrial Technique Institute, Japan as JSPS fellow (2000-2001), IFW Dresden as AvH fellow (2001-2002) and Max-Planck Institute of Metal, Stuttgart as visiting scientist (2003). He research areas include mechanical behaviors of metallic materials, especially focusing on fatigue and fracture mechanisms. He has proposed Unified tensile fracture criterion, which unified the classical fracture criteria in the textbook of materials mechanics. Recently he had fabricated the AM Ti alloy with the highest specific fatigue strength in the world. He has published more than 600 papers in international SCI journals, including Nature, Science, Nature Mater, Prog. Mater. Sci., Phys. Rev. Lett., Acta Mater. etc. These papers have been cited more than 25000 times by SCI papers. He had been awarded by National Fund for Distinguished Young Scholars, Major National Natural Science Project, National Special Talent Support Program, Special government allowance of the State Council and Liaoning May Day Labor Medal.

Invited Lecture: Unified tensile fracture criterion

Abstract: Owing to the unique amorphous structure, metallic glasses (MGs) exhibit quite distinctive deformation and fracture behaviors from the conventional crystalline materials. This study is based on the research works of the authors on the fracture and strength of MGs in the past two decades, and concentrates on discussing the current knowledge and recent advances on the fracture behavior and strength theory of ductile and brittle MGs. We find that the classical failure criteria, i.e. maximum normal stress criterion, Tresca criterion, Mohr-Coulomb criterion and von Mises criterion, cannot satisfactorily explain the tensile fracture behavior of the bulk metallic glass (BMG) materials. For a better description, we propose an ellipse criterion as a new failure criterion to unify the four classical criteria above and apply it to exemplarily describe the tensile fracture behavior of BMGs as well as a variety of other materials. It is suggested that each of the classical failure criteria can be unified by the present ellipse criterion depending on the difference of the ratio . Then considering the fundamental principles of material fracture, we theoretically derived the unique equation forms for the first three-order fracture criteria. Employing molecular dynamics (MD) simulations on the two typical metallic glasses, Cu₆₅Zr₃₅ and Ni₆₂Nb₃₈, under three-axis loading, the critical normal and shear stresses on the shear band plane were obtained at the point of shear instability. A comparative analysis between the derived fracture criteria and MD simulation results revealed that the two-order (2-O) fracture criterion exhibits the best agreement with the shear instability of metallic glasses. Therefore, this work concludes that the 2-O fracture criterion is the optimal choice within the polynomial range for the unified fracture criterion.