J' Y' NAM, J' B' CHOI AND Y' J' KIM

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DEVELOPMENT OF A FIBER-OPTIC AE SENSOR
FOR ON-LINE MONITORING SYSTEM
J. Y. NAM, J. B. CHOI AND Y. J. KIM School of
Mechanical Engineering, Sungkyunkwan Univ.
Presented at the 2004 ASIAN PACIFIC CONFERENCE ON
FRACTURE AND STRNGTH04 JEJU, KOREA OCTOBER 7,
2004
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Background I
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Background II
lt Related research gt

• Kim (1993)
• Detected AE signals using Michelson
  interferometer with a
• compensating circuit of lighting-path
  difference

• Caloran (1997)
• AE sensor using fiber-optic Sagnag
  interferometer for a power plant

• Janzen (1995)
• Acoustic and vibration sensor using Extrinsic
• Fabry-Perot interferometer

- Uses high cost equipment - Difficulties in
remote control
not suitable for industry application
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Objectives

• Development of a fiber-optic AE sensor for
  on-line
• monitoring system

- Suitable for long-distance signal
transmission without external noise - Suitable
for industry application - Applying laser
interferometer type
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AE SENSOR I

• A schematic diagram of AE sensor

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AE SENSOR II

• Principle of the developed AE sensor

Source of AE(S)
Resonance of Cantilever(R)
Laser interferometer(I)
Output of AE signal(A) ASRI
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AE SENSOR III

• Response of AE sensor(A) - mathematically

Where,
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AE SENSOR IV

• Design of AE sensor (II)

• Cantilever length - 9.4mm, natural frequency -
  1.06kHz
• Light source wavelength - 800nm, Pmax 1.5mW

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EXPERIMENTS I

• Experiments

• 1. PLF test
• Pencil lead diameter 0.5mm
• Fiber optic sensor 40dB amplified.
• PZT sensor raw signal

PZT sensor
Fiber-optic sensor
Pencil lead break
200 mm
10 mm
SM45C
200 mm
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EXPERIMENTS II

• 2. Tensile test
• To verify the developed sensor by detecting
  signals
• emitting from plastic deformation
• To verify the detecting ability of AE signals
  due to the Kaiser effect

Specimen
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EXPERIMENTAL RESULTS I

• PLF testing(I) time region

(a) Fiber-optic sensor signals (40dB
amplified) - Low range frequency(about 1kHz )
(b) PZT sensor signals - Vibration signals(low
frequency)
(c) Theoretical solution - Signals of resonant
frequency(1.06kHz)
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EXPERIMENTAL RESULTS II

• PLF testing(II) frequency analysis

(a) Fiber-optic sensing signals - Detected peak
signal of resonant frequency(1.06kHz) -
Peak amplitude at 740Hz(4.9dB)
(b) PZT sensing signals - Peak amplitude at
740Hz(0.56dB)
(c) Theoretical solution - Peak amplitude at
1.06kHz
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EXPERIMENTAL RESULTS III

• Tensile testing

The variation of rms voltage and applied load
for tensile test
The variation of rms voltage showing the Kaiser
effect
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CONCLUSION

• A fiber-optic AE sensor was developed which is
  suitable for on-line
• monitoring system and long-distance signal
  transmission.
• The developed sensor drove signals of a few
  hundreds kHz into those
• of about 1kHz by using the resonance of a
  fiber-optic cantilever, and
• results in improvement of signal processing
  efficiency.
• The developed sensor was more sensitive in
  detecting crack propagation
• than the elastic-plastic deformation of the
  tested material and could
• detect the Kaiser effect effectively.