Experimental studies were conducted on the dynamic fracture behavior of
AISI 5140 steel over a wide range of loading rates. True stress-strain
relations of the steel were measured under different strain rates, and a
dynamic constitutive model was then expressed with the strain-hardening
term and the strain-rate hardening term. Fracture tests were
investigated under quasi-static condition, instrumented Charpy impact
condition and Hopkinson pressure bar impact condition. Fracture
toughnesses corresponding to each test condition were also determined.
Fracture characteristics were analyzed with observations of the fracture
appearances. It was found that the fracture toughness decreased
significantly with the increasing loading rate, and the fracture
mechanisms of the steel at various loading rates were brittle fractures
characterized by river markings and secondary cracks. Based on the
fracture assessment method of the CEGB R6 procedure, the effects of the
strain rate and the loading rate on the assessment curve were discussed.