Some Considerations on the Notched Bar Impact Test (1st Report )

Abstract

Series of double blow impact test were performed on V-notched Charpy specimens at temperatures, -50°C to 70°C. The depths of cracks created by first light blows. were detected by dripping etching solution at the notch roots of specimens and then breaking them by the second standard blows, which demonstrated the energy for propagating these cracks. Also, standard single blow Charpy test was carried out at the same testing temperature. Combining these three energy values, the effects of velocity diffeerences were eliminated from the first light blows. Series of tests were made at a settled temperature, with varying amounts of energy by first blow, thus the energy for crack initiation could be determined. The same steps were taken at different test temperatures.
The Fig. 3, 4 and 5 show the experimental results. From those figures, the effects of temperature on the energies for crack initation (Wi) and porpagation (Wp) were determined as in Figs. 6, 7 and 8. Then, the meannings of 15 ft-lbs or 1/2 maximum energy transition temperatures could clearly be understood. Also the percent shear-temperature curves in Fig. 12 were proved to possess close correlations with the Wp-temperature curves. For three kinds of steels investigated, the orders of the locations and the maximum values of Wi-temperature curves coincided well with those of WP-temperature curves. But there was no correlation between the order of location and the maximum values of Wi or Wp-temperature curves in the three steels. Further, the effects of impact velocities on Wi and Wp at various temperatures were discussed making use of the test results in Figs. 3-5.