切欠を付したフェライト基地球状黒鉛鋳鉄の靭性特性に及ぼす負荷速度の影響

抄録

  This study aims to clarify the influence of loading speed on toughness in ferritic spheroidal graphite cast iron with various notches. The toughness was measured by means of the Charpy impact test and static bending test. The specimens used were impact and bending test specimens with various notches; un-notch (stress concentration factor:α= 1.0), U-notch with 2 mm depth and 0.5 mm root-radius (α= 3.0), U-notch with 2 mm depth and 0.15 mm root-radius (α=4.8), and fatigue-crack with 2 mm depth. The tests were performed at various loading speeds from 1.67×10^-5 m/s to 5.2 m/s in the temperature range from 123 K to 298 K. The results obtained are as follows:
  In the ductile region, the fracture energy at a higher loading speed is larger than that at a slower loading speed. The transition temperature region of the bending test is lower than that of impact test at any loading speed. Therefore, at the temperature of 223 K, every notched specimen shows that the fracture energy by the bending test is larger than that by the impact test, which is because every specimen of the im-pact test plunges into its transition temperature region at this temperature. Only a small difference is observed in the load-displacement curves of the specimen with a notch of α=4.8 and the specimen wi th fatigue-crack. The transition temperature of the specimen with fatigue-crack is very similar to those of the specimen with notch of α=4.8. The influence of external notches on toughness increases with increasing loading speed.