1. Department of Aerospace Engineering, Advanced Composites Centre for Innovation and Science, University of Bristol, Bristol BS8 1TR, UK e-mail:
2. Joyce and Kent Kresa Professor of Aeronautics and Professor of Civil Engineering, Graduate Aerospace Laboratories, California Institute of Technology, Pasadena, CA 91125 e-mail:
3. Professor in Lightweight Structures, Department of Aerospace Engineering, Advanced Composites Centre for Innovation and Science, University of Bristol, Bristol BS8 1TR, UK e-mail: