Electromagnetic Wave Emission in Uniaxial Compression Testing.

Abstract

A number of studies on electromagnetic wave emission from fractured rocks have been heretofore carried out. By many authors it was pointed out that rock fracturing or acoustic emission could be concerned with electromagnetic wave emission. However, the origin of electromagnetic wave emission is still not well understood.In this study electromagnetic wave from rocks was measured with a radio interference measuring apparatus during uniaxial compression testing under several kinds of loading conditions. Firstly, the uniaxial compression testing under constant strain rate of 10 -4 s -1 was conducted for seven rocks. It was found that Inada granite, Honkomatsu andesite and Kuzuu dolomite emit electromagnetic wave. However electromagnetic wave cannot be detected for Sanjome andesite, Akiyoshi marble, Kimachi sandstone and mortar.Secondly, electromagnetic wave emission was investigated under several experimental conditions. It was found that Inada granite emits electromagnetic wave during uniaxial compression testing under a constant strain rate of 10 -5 s -1 and under a constant rate of (stress -strain / Young's modulus). In most cases, electromagnetic wave emission was accompanied with sudden decrease of stress. By analysis on results of the uniaxial compression testing under constant strain rate, it was found that electromagnetic wave emission is closely related to cracking or crack extension.The main results in this study can be summarized as follows; 1) Amplitude of electromagnetic wave is relatively large for strong rock.2) For Inada granite, the larger the stress drop occurred in uniaxial compression test is, the larger the amplitude of electromagnetic wave. 703〈 7 〉

Fracture Behavior Accompanying Electromagnetic Waves of Granite in Dynamic Three Point Bending

“…From this figure, it can be found that the slope, P/δ, during the increase of load and the maximum load observed in dynamic test are greater than those obtained from static test. Similar results were obtained in the range of quasi-static tests (8) . This means that the mechanical properties of granite greatly depend on the loading rate.…”

“…To remove the noise of high and low frequencies, we used a band pass filter with a frequency band of 284 ~1000 kHz, after amplifying the output from the antenna to 100~1000 times by a differential amplifier. The reasons for the choice of 284 ~1000 kHz are that the frequency band was used for the measurement in the past work (8) , and that relatively less noise around 500 kHz was obtained in our laboratory.…”

Impact compressive and bending behaviour of rocks accompanied by electromagnetic phenomena

“…These figures show that the theory of a piezoelectric effect in quartz may be more reasonable and predominant than the frictional electrification theory. In addition, because it was previously demonstrated that electromagnetic emission could not be observed in the fracture of marble [12,23] and the intensity of electromagnetic emission depends on the content of quartz, as shown in figures 11-14, we can say that the theory of the piezoelectric effect of quartz is one of the most reasonable mechanisms for the electromagnetic emission generated in the fracture of granite and gabbro. Of course, several other mechanisms can still be considered in various different situations.…”

“…The reason for the choice of the frequency band, i.e. 284-1000 kHz, was that the band contained relatively less noise in our laboratory and has already been used for similar measurements in previous work [12].…”

“…Electromagnetic wave emission has various potential geophysical applications, such as research into the electromagnetic phenomena associated with earthquakes [2][3][4][5][6][7][8][9], investigation of the Earth's crust, monitoring cracks in rock deformation experiments [10,11] and so on. In order to elucidate the electromagnetic phenomena during fracture of several rocks, including granite and andesite, quasi-static compression tests were carried out and acoustic emission was also measured [12][13][14][15][16]. The majority of previous works concerning electromagnetic phenomena during the deformation and fracture of rocks have been performed under 'static' and 'compressive' loading.…”