1. Departments of Civil and Environmental Engineeringand Mechanical Engineering; Center for Engineering and Healthand Skin Disease Research Center, Northwestern University; Evanston IL 60208 USA
2. Center for Mechanics and Materials; Tsinghua University; Beijing 100084 China
3. Department of Materials Science and Engineering, Frederick Seitz Materials Research Laboratory; University of Illinois at Urbana-Champaign; Urbana IL 61801 USA
4. School of Aerospace Engineering and Applied Mechanics; Tongji University; Shanghai 200092 China
5. Institute of Solid Mechanics; Beihang University; Beijing 100191 China
6. Department of Materials Science and Engineering Chemistry, Mechanical Science and Engineering, Electrical and Computer Engineering; Beckman Institute for Advanced Science and Technology and Frederick Seitz Materials Research Laboratory; University of Illinois at Urbana-Champaign; Urbana IL 61801 USA