1. Division of Solid Mechanics, Lund Univ., P.O. Box 118, SE-221 00 Lund, Sweden (corresponding author).
2. Dept. of Materials and Manufacturing Technology, Chalmers Univ. of Technology, SE-412 96 Göteborg, Sweden.
3. Division of Solid Mechanics, Lund Univ., P.O. Box 118, SE-221 00 Lund, Sweden.