A dynamic small punch (DSP) tester has been developed. DSP specimens are dynamically loaded by hitting an input bar through a striker bar which is accelerated by an air gun. The maximum speed of the striker bar is 13 m/s. Load and deflection are measured with two foil strain gages attached to the input bar and the deflection sensor, respectively. The fracture energy of the DSP test is determined from the total area under the load versus deflection curve up to the maximum load point. The ductile-brittle transition behavior of turbine rotor steels has been investigated by means of the DSP tester. The ductile-brittle transition temperature (DBTT) is determined on he basis of the variation of the DSP energy with testing temperatures. SEM observations of fractured surfaced have shown that the fracture mode transition and the DSP energy transition are consistent. The effect of strain rate on the DBTT is also examined. Based on these results, the relationship between the DBTT obtained from the DSP tests and that from the Charpy V-notch (CVN) impact tests is discussed as a function of strain rate.
