J/sub 1c/ fracture toughness transition behavior of HT-9

Small compact tension specimens of two heats of HT-9 were tested at temperatures ranging from room temperature to -1920C. The ductile-brittle transition toughness of HT-9 was evaluated using the J-integral approach. There were two loading rates of 2.1 x 10-5 m/s and 3.2 x 10-2 m/s. The ductile-brittle transition temperatures of HT-9 (number 1 heat) tested at 2.1 x 10-5 m/s and HT-9 (number 2 heat) tested at 3.2 x 10-2 m/s were found to be -60 and -100C, respectively. Results showed the fracture toughness of the former was not sensitive to loading rate and the lower shelf toughness decreased with temperature to a J/sub 1c/ value of 5 kJ/m2 at -1900C. Furthermore, the values of J/sub 1c/ were valid since the thickness of the test specimens was well above the thickness criterion