Electromagnetic and Acoustic Emission Fine Spectra

článek v časopise - ostatní, Jost

angličtina

The new measuring method for detection of small cracks fine spectra of electromagnetic and acoustic emission (EME and AE) signals is described. It requires wide band ultra-low noise amplifiers, analogy filters, optimization of signal to noise ratio of sensors and application of noise elimination methods. The analyses of noise sources in sensors and preamplifiers are given. They are thermal noise, polarization noise and low frequency 1/f noise. Measuring set-up background noise suppression including electromagnetic shielding allows us to detect signals in the range of 100 nV. This measuring set-up was used to observe crack creation in granite samples. AE and EME signals show different behaviour in the first interval of about 10 s just after crack creation. In frequency domain EME spectra show that in the first stage of crack creation the spectrum is given by crack walls eigen vibration, internal friction and sample electrical conductivity. We observed that crack opening and crack wall vibration create high frequency signal in the frequency band up to 10 MHz. These signals were observed in time period of 10 s. In the second period for time interval 10 to 300 s the frequency spectrum is given by sample eigenvibration or sample boundary conditions and we observed spectra in the frequency range 100 kHz to 2 MHz. In this second period EME signal amplitude depends on sample electrical conductivity and with increasing conductivity decreases.

Acoustic emission, electromagnetic emission, crack

Josef Sikula, Jiri Majzner, Petr Sedlak and Yasuhiko Mori

2006

18. 9. 2006

1022-6680

Advanced Materials Research

2

13-14

Švýcarská konfederace

169

174

6

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