1. Department of Mechanical Engineering, University of Michigan, 2271 G. G. Brown Laboratory, 2350 Hayward Street, Ann Arbor, MI 48109 e-mail:
2. Stephen P. Timoshenko Collegiate Professor ASME Fellow Department of Mechanical Engineering, University of Michigan, 2236 G. G. Brown Laboratory, 2350 Hayward Street, Ann Arbor, MI 48109 e-mail: