1. Department of Engineering Science and Mechanics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
2. Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87845, USA
3. Department of Mechanical Engineering, University of New Hampshire, Durham, New Hampshire 03824, USA
4. Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio 45433-7817, USA