Dynamic fracture toughness measurements of ferritic ductile cast iron

Fracture toughness testing of ductile cast iron (DCI) at elevated loading rates has been performed at Sandia. The intent of the test program was to generate rigorously measured dynamic fracture toughness data in order to enhance the DCI material property data base and to evaluate the effect of rate on the upper-shelf fracture toughness. The test requirements outlined in the ASTM Standard Test Method for J/sub Ic/, A Measure of Fracture Toughness (E 813-87) were adapted to elevated loading rates in a manner which allowed the inherent rigor of this test method to be maintained. The actual measurements were performed on compact tension specimens using a closed-loop servo-hydraulic test frame with special fixturing to enhance test control. The DCI alloy examined was a high quality casting of the type used in European-produced casks (i.e., it had a fully ferritic matrix, with only Type I and II graphite nodules). The test results show that there is essentially no effect of loading rate on the upper-shelf fracture toughness over the range tested. The current results are in contrast to other reports which suggest that there is a decrease in the upper-shelf toughness as the loading rate is raised above a certain level. 11 refs., 4 figs