石炭の疲労破壊に伴うガス透過性の不可逆変化 ＡＥ法による石炭のガス透過性に関する研究 （第４報）

Abstract

In the fatigue tests of coals the changes in gas permeability and acoustic emission activity have been monitored in order to obtain an index of the occurrence of unclosing cracks. Actually at the final stage of fatigue fractures the acoustic emission activity occurred in the unloading process in the same manner as that in the loading process and the amplitude-frequency distribution of acoustic emissions changed from a simple straight line to three straight lines broken at two points. These facts proved that opening cracks in which some fragments were caught turned out to unclosing cracks. From the above monitored results, it became clear that the gas permeability of the unclosing cracks did not depend on the external stresses. Moreover, it was confirmed that the characteristic of the amplitude-frequency distribution of acoustic emissions was useful for judging the occurrence of unclosing cracks.