岩石の衝撃圧縮および曲げ変形における強度と電磁的現象

概要

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In order to investigate the relationship between the mechanical properties of rocks and the electromagnetic phenomena during their fracture, uni-axial compression and three-point bending tests for two kinds of rocks, granite and gabbro, with different content of quartz were carried out at quasi-static and dynamic rates. Not only the stress-strain or load-deflection curve but also the output of ferrite-core antenna located close to specimens in a shielding box made of Permalloy plates, which indicates the magnitude of electromagnetic wave, were measured through a band-pass filter. The dynamic compressive and bending strengths were larger than those in static tests and there is strain-rate dependence in their strength of both rocks. It was also found that the intensity of electromagnetic waves measured in dynamic compression tests for granite was much greater than that observed in static tests, i.e. the electromagnetic phenomenon strongly depends on loading rates, too. Even in dynamic bending tests for granite, relatively large electromagnetic waves were observed as well as in compression tests. This fact cannot be explained by the frictional electrification theory, because the bending fracture usually occurs under mode I, i. e. without rubbing of crack surfaces.