1. AML, Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China;
2. Center for Mechanics and Materials, Tsinghua University, Beijing 100084, China
3. Center for Mechanics and Materials, Tsinghua University, Beijing 100084, China e-mail:
4. State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China