1. Institute for Soldier Nanotechnologies, Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, Institute for Soldier Nanotechnologies, Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, and Multi Scale Mechanics, TS, CTW, Universiteit Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands