Experimental study on the material dynamic fracture properties by Instrumented Charpy Impact test with single specimen method

With the determination of load-time curve recorded by Amsler/Roell RKP 450 Instrumented Charpy Impact test and based on the Newton's Second Law, Impact character of a single standard V-notch specimen of X70 pipeline steel under the low temperature -70degreesC was investigated by studying the impact energy distribution. It was revealed that maximum load point (F-m point) was not exact the dynamic crack initiation, which was detected somewhere prior and very close to F-m point by using Compliance Changing Rate method. This fact was also confirmed by Dynamic CTOD method. That is to say, Impact energy related to the F-m point (i.e. E-m) consists not only the crack initiation energy E-i, but a small part of crack extension energy as well. Ratio of E-i/E-m was found to be 0.90 just applicable to the material used here. Dynamic fracture toughness J(1d) was then estimated by modified Rice equation. Crack extension behavior and dynamic crack growth resistance curve (J-Deltaa) during stable crack propagation period was carefully analyzed by Key Curve method. Finally, methods for evaluating tearing module T-max and CTOD curve under the impact test were also briefly introduced in the paper.