Electromagnetic Wave Emission in Uniaxial Compression Testing
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.
Key Words: Rock, Uniaxial Compression Testing, Electromagnetic Wave, Crack, Post-Failure Region