Evaluation of the Fracture Toughness of Ductile Iron Using Fatigue Precracked Charpy, Dynamic Tear, and Compact Tension Specimens

The fracture toughness of ductile iron has been studied using dynamic tear, fatigue precracked (FPC) Charpy, and compact tension (CT) specimens. Specimens were fractured both quasi-statically and dynamically. Initial crack extension was found to occur at maximum load for both the compact tension specimens and the FPC Charpy specimens. However, initial crack extension occurred prior to maximum load for the dynamic tear specimens. Upper-shelf KJIc values determined from the compact tension specimens and the FPC Charpy specimens were similar (83 and 76 MPa √m) while the J-value at maximum load for the dynamic tear specimens was found to fit nicely on the J-R curve from the CT specimens. The shift in ductile-to-brittle transition temperature with strain rate (comparing quasi-static with impact loading) was similar to what has been observed for structural steel with a similar yield strength.