Loading rate effect on ductile crack resistance of steels using precracked Charpy specimens R. Chaouadi a, b, * , J.L. Puzzolante a a SCKCEN, Boeretang 200, 2400 Mol, Belgium b Forschungszentrum Ju ¨lich, Euratom Association, IEF-2, D-52425 Ju ¨lich, Germany article info Article history: Received 27 November 2007 Received in revised form 6 August 2008 Accepted 7 August 2008 Keywords: Loading rate Quasi-static Dynamic Ductile fracture Crack resistance Fracture toughness Charpy impact Precracked Charpy Crack growth correction J R -curve Loss of constraint abstract While loading rate effects were extensively investigated in the transition regime where fracture occurs in a brittle manner, they are comparatively much less studied in the ductile regime. The main objective of this paper is to provide experimental data on the effect of loading rate on the ductile fracture behavior and examine the relation that might exist between the various material properties. In particular, the crack resistance behavior of two ferritic steels, A533B plate and 20MnMoNi55 forging, at quasi-static and dynamic (impact) loading rates was examined. As expected, the results clearly show that the ductile crack resistance at dynamic loading rate is systematically and significantly higher than at quasi-static loading rate. Moreover, at the upper shelf plateau, while dynamic crack resistance is nearly constant, ductile resistance decreases with temperature at static loading rates. This can be associated with the strain rate sensitivity of the material and the inertial effects inducing a significant loss of constraint (loss of triaxiality). By taking these effects into account, the experimental results were rationalized. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction There has always been a large interest by the structural mate- rials scientists to derive fracture toughness from other more simple tests, such as tensile and Charpy impact tests, than from the more complicated fracture toughness tests. As a result, a number of correlations were proposed in the literature [1–4] with more or less success. Actually, most of these empirical or semi-empirical rela- tions provide reasonable agreement with experimental data in a very limited range of application. In this work, the main objective is not to provide such empirical relations. Instead, the aim is to investigate the property-to-property correlation. Indeed, we believe that most of the mechanical properties can be correlated with one another if the underlying mechanisms are well under- stood. As a result, such correlations offer a ‘‘quality control tool’’ to experimental data. This is very important in the nuclear materials field where very often limited tests are available, mainly few Charpy impact, tensile and more rarely fracture toughness data. The basic idea is that all these properties should indicate a consistent and unique behavior. The consistency between the various prop- erties is extremely important to better understand the material behavior. If inconsistent, the conclusions that might be drawn will be definitely questionable. Loading rate effects were extensively investigated in the tran- sition regime where fracture occurs in a brittle manner. It is well known that at high loading rates, the fracture toughness transition curve shifts to higher temperatures. As a result, the required energy for crack initiation decreases with increasing loading rate. However, the ductile regime was comparatively much less inves- tigated from this aspect. Of course, from a structural integrity point of view, this is not so critical in comparison to the transition regime where fracture occurs in a brittle manner. However, most of the structural components operate over their lifetime in a temperature range of ductile regime. It is therefore important to well charac- terize these materials also in the ductile regime. Among the empirical correlations previously mentioned, one of the most known is the one estimating fracture toughness from the Charpy impact energy [2,4–7]. The upper shelf energy and the static yield strength are generally used to predict static fracture tough- ness. As it can be seen, this is one of the inconsistencies of such a correlation in the sense that static fracture toughness is derived * Corresponding author. SCKCEN, Boeretang 200, 2400 Mol, Belgium. Tel.: þ32 14 333 465; fax: þ32 14 321 529. E-mail address: rachid.chaouadi@sckcen.be (R. Chaouadi). Contents lists available at ScienceDirect International Journal of Pressure Vessels and Piping journal homepage: www.elsevier.com/locate/ijpvp 0308-0161/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijpvp.2008.08.004 International Journal of Pressure Vessels and Piping 85 (2008) 752–761