多能衝撃試験機の開発と衝撃強度の新表示法

抄録

In order to express impact strength of materials in stress unit over a wide range of impact velocity, a new testing method is proposed. The experimental apparatus used in this study was composed of a gas gun and a loading apparatus for impact tension or impact bending test. Fracture strength was evaluated based on the strain history measured by the strain gage cemented on a specimen. Commercial JIS. SS41 carbon steel specimens were used to show the usefulness of this new testing apparatus. In order to carry out impact tension or impact bending test, a plate or conventional Charpy specimen conforming to JIS. 5 was used, respectively. A strain gage was cemented on the central portion or notch root of each type specimen. Then, impact bending strength was expressed by the nominal stress taking the stress concentration by the notch into account. Thus, the experimental results were expressed in stress unit instead of energy unit. By using this apparatus, low temperature tests can be carried out under more strictly controlled temperature conditions in comparison with a pendulam type tester such as Charpy impact tester.
The impact tensile strength I_{m, t} and the impact bending strength I_{m, b} evaluated by this method increased with an increase in impact velocity. At low temperature, I_{m, t} was higher than that of room temperature. These impact strengths, I_{m, t} and I_{m, b}, took the values of about 2 GPa at the impact velocity of 80m/s. For the lower impact velocity range, the impact bending strength was slightly lower than the impact tensile strength at 77K.