1. Institute of Hybrid Materials, National Center of International Joint Research for Hybrid Materials Technology, National Base of International Sci. & Tech. Cooperation on Hybrid Materials, College of Materials Science and Engineeeing, Qingdao University, 308 Ningxia Road, Qingdao 266071, China
2. Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC 27695, USA