破壊靭性試験における人造黒鉛電極材の巨視亀裂発生点の判定

抄録

Judgment of macroscopic crack initiation points (MCIP) in artificial graphite electrodes in fracture toughness tests was discussed by crack gage, acoustic emission (AE) and electrical potential (EP) methods. It is concluded that the crack gage method was not suitable for identifying MCIP, because MCIP was located beyond the maximum load point (P_m) in most cases. In the EP method, the initial increase of EP could not be regarded as MCIP, because generation of microcracks under low-level loading raised EP. Although another procedure to determine MCIP by the EP method was tried, it is concluded that the EP method is unsuitable. Usually, an abrupt increase in accumulated AE energy was regarded as MCIP in the AE method. Even though many abrupt increases were observed, the judgment of abrupt increase corresponding to MCIP was possible, by introduction of AE energy, which was a value of multiplied amplitude of AE observed by its duration, and a proper threshold value. As a result, it was concluded that the AE method was useful for the judgment of MCIP in artificial graphite electrodes. These loads of MCIP are about 88% of those of P_m's.