1. Laboratory of Fatigue and Fracture for Materials Institute of Metal Research Chinese Academy of Sciences Shenyang 110016 China
2. School of Materials Science and Engineering University of Science and Technology of China Hefei 230026 China
3. Key Laboratory of Bionic Engineering (Ministry of Education) College of Biological and Agricultural Engineering Jilin University Changchun 130022 China
4. Department of Materials Science and Engineering University of California Berkeley Berkeley CA 94720 USA