Identification of CTOA and fracture process parameters by drop weight test and finite element simulation

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, governing the process zone of the material under investigation, have to be determined: the process zone dimension (named “Δ distance”) and the critical value of crack tip opening angle (CTOA). CTOAC can be determined through an experimental 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, Δ 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.