Identification of CTOA and fracture process parameters by drop weight test and finite element simulation P. Salvini a,1 , A. Fonzo a, * , G. Mannucci b,2 a Department of Mechanical Engineering, University of Rome ‘‘Tor Vergata’’, Via del Politecnico n. 1, 00133 Rome, Italy b Centra Sviluppo Materiali S.p.A. Via di Castel Romano n. 100/102, 00128 Rome, Italy Received 30 July 2001; received in revised form 13 February 2002; accepted 6 March 2002 Abstract This paper presents a new technique that is able to predict ductile fracture propagation occurrences in large metallic structures, by means of an appropriate application of the finite element modelling. This technique takes account of a cohesive zone in the vicinity of the crack tip, where a nodal release technique is implemented. Two parameters, gov- erning the process zone of the material under investigation, have to be determined: the process zone dimension (named ‘‘D distance’’) and the critical value of crack tip opening angle (CTOA). CTOA C can be determined through an ex- perimental laboratory procedure two specimen CTOA test (TSCT) that is already known and used by researchers who study fracture propagation on pipelines [Demofonti G, et al. Step-by-step procedure for the two specimen CTOA test. In: Proceedings of the Second International Conference on Pipeline Technology, Ostend, vol. II. 1995]. The second parameter required, D distance, is determined minimizing the differences of Finite Element results towards experimental data of an instrumented impact test (drop weight tear test). Some interesting improvements, concerning distinction between the initiation energy and the propagation energy accounted in TSCT procedure, are also discussed, in order to successfully extend its use to both high strength and high toughness steels. Ó 2002 Elsevier Science Ltd. All rights reserved. Keywords: Ductile fracture; Cohesive zone model; Drop weight tear test; Crack tip opening angle; Essential work of fracture 1. Introduction Ductile crack propagation in metals is accompanied with an extended plastic zone ahead the crack tip, particularly when thickness is small compared to other dimensions. If the driving force does not decrease during crack propagation, the fracture can widely extend, as it can effectively happen in pressurized pipelines suffering longitudinal cracks. Such events are characterised by a high dynamics, so that the central difference scheme for finite element solution is well suited. In the field of the engineering structures here Engineering Fracture Mechanics 70 (2003) 553–566 www.elsevier.com/locate/engfracmech * Corresponding author. Fax: +39-6-2021351. E-mail addresses: salvini@uniroma2.it (P. Salvini), fonzo@ing.uniroma2.it (A. Fonzo), g.mannucci@c-s-m.it (G. Mannucci). 1 Fax: +39-6-2021351. 2 Fax: +39-6-5055452. 0013-7944/03/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. PII:S0013-7944(02)00137-6