1. Vallourec Competence Center Rio 485 Paulo Emídio Barbosa St. Rio de Janeiro RJ 21941‐615 Brazil
2. Laboratory of Fracture MechanicsCOPPE/Federal University of Rio de Janeiro PO Box 68505 Rio de Janeiro RJ 21941‐972 Brazil
3. Fracture Mechanics GroupNational University of Comahue/CONICET 1400 Buenos Aires St Neuquén Q8300IBX Argentina
4. Department of Mechanical EngineeringPolitecnico di Milano Via La Masa 34 20156 Milan MI Italy