13:45 〜 15:15
[SCG46-P06] Acoustic emission monitoring at high pressures using a broadband piezoelectric transducer combined with a D-DIA apparatus
キーワード：アコースティックエミッション、広帯域型センサ、D-DIA型変形装置
It is well known that acoustic emissions (AEs), which are the elastic waves generated from the propagating crack tips, satisfy the same scaling relationship as natural earthquakes from the viewpoint of seismic moment and corner frequency (Yoshimitsu et al., 2014), namely, AE is a good simulation of actual earthquake events. Frequencies of AE waveforms range from 100 kHz to 5 MHz, and thus broadband-type AE sensors are required for seismological frequency analyses. On the other hand, use of prevalent resonant-type AE sensors, which record a narrow frequency band, is limited to determination of the 1st arrival time and wave amplitudes. Because both number and size of AE sensors are strongly restricted in AE monitoring combined with a multianvil apparatus, AE monitoring using a broadband AE sensor has not been performed at high pressures. Here, we have devised an AE monitoring system designed for a deformation-DIA apparatus, which consists of five resonant-type AE sensors and a broadband-type AE sensor. The former ones were used for determination of AE hypocenter location and the latter one was used for analysis of waveform frequencies.
We conducted cold-compression runs on quartz-beads samples using a deformation-DIA apparatus installed at Geodynamics Research Center, Ehime Univ. Quartz beads were packed into a nickel capsule (0.8-3 mm in diameter; 1-4 mm in length). The quartz-beads samples were compressed up to about 3 GPa at room temperature. AEs radiated from the sample propagates in the cell assembly and anvils surrounding the sample and then detected by six AE sensors.
Our experimental results showed that AE hypocenter locations were determined with an uncertainty of about ±1 mm in the case of larger samples (1.5-3 mm in diameter; 2-4 mm in length). However, determination of hypocenter locations of AEs from smaller samples was not successful, due to not enough number of resonant-type AE sensors (i.e., 5). We found that frequencies of AE waveforms concentrate to the range from 0.2 to 0.8 MHz. The range of frequency is much lower than the resonant frequency (~4 MHz) of the resonant-type AE sensors. We also performed annealing experiments on the quartz-beads samples at 600 °C. Unfortunately, an ultra-small preamplifier in the broadband-type AE sensor was damaged under high-temperature conditions (~100 °C around the 2nd-stage anvil) and thus frequencies of AE waveforms were not determined. Our AE monitoring system requires further efforts to optimize the combination of broadband-type AE sensor and preamplifier under high-temperature conditions.
We conducted cold-compression runs on quartz-beads samples using a deformation-DIA apparatus installed at Geodynamics Research Center, Ehime Univ. Quartz beads were packed into a nickel capsule (0.8-3 mm in diameter; 1-4 mm in length). The quartz-beads samples were compressed up to about 3 GPa at room temperature. AEs radiated from the sample propagates in the cell assembly and anvils surrounding the sample and then detected by six AE sensors.
Our experimental results showed that AE hypocenter locations were determined with an uncertainty of about ±1 mm in the case of larger samples (1.5-3 mm in diameter; 2-4 mm in length). However, determination of hypocenter locations of AEs from smaller samples was not successful, due to not enough number of resonant-type AE sensors (i.e., 5). We found that frequencies of AE waveforms concentrate to the range from 0.2 to 0.8 MHz. The range of frequency is much lower than the resonant frequency (~4 MHz) of the resonant-type AE sensors. We also performed annealing experiments on the quartz-beads samples at 600 °C. Unfortunately, an ultra-small preamplifier in the broadband-type AE sensor was damaged under high-temperature conditions (~100 °C around the 2nd-stage anvil) and thus frequencies of AE waveforms were not determined. Our AE monitoring system requires further efforts to optimize the combination of broadband-type AE sensor and preamplifier under high-temperature conditions.