1. The George W. Woodruff School of Mechanical Engineering Georgia Institute of Technology Atlanta GA 30332 USA
2. Renewable Bioproduct Institute Georgia Institute of Technology Atlanta GA 30332 USA
3. College of Engineering Peking University Beijing 100871 P. R. China
4. Applied Mechanics and Structure Safety Key Laboratory of Sichuan Province School of Mechanics and Engineering Southwest Jiaotong University Chengdu Sichuan 610031 P. R. China