Loading rate effect on ductile crack resistance of steels using precracked Charpy specimens

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.