AE09.pdf

Remote monitoring an acoustic emission waveform and

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Remote Monitoring An acoustic emission waveform and strain monitoring system was developed and installed on a bridge for weeks. 10 The system recorded acoustic emission waveforms from two wide band acoustic emission transducers only during specified portions of truck loadings as determined by strain gage monitoring. Periodically, the system reported remotely to a laboratory system, downloaded stored data files and occasionally uploaded a modified monitoring protocol. No acoustic emission believed to be caused by crack growth was detected and no crack growth was observed during the three-month monitoring period, even though many acoustic emission waveforms were recorded. The Federal Highway Administration sponsored the development of a bridge monitoring system that could collect acoustic emission waveforms and strain gage signals and report the data remotely to a base station. The local area monitoring system developed was battery powered and could report through a cellular telephone modem. A prototype of this system was used to monitor persistent cracking in the Coleman Bridge, Yorktown, Virginia. The problem is described elsewhere in the literature. 11 Acoustic emission monitoring seems ideally suited for detecting crack growth in steel bridge structures. One study included laboratory testing and field monitoring 12,13 A steel bridge hanger with three fatigue cracks was monitored for acoustic emission using combined source location, strain gage monitoring and waveform analysis (Fig. 5). Results from laboratory tests on Unified Numbering System K11430 (ASTM A588) alloy steel, compact tension specimens under variable amplitude tension fatigue loading were used to aid in interpreting acoustic emission data from the hanger (Fig. 6). Crack growth acoustic emission from these tests were detected only on overload cycles mostly above 92 percent of maximum load whereas acoustic emission from crack face 310 Acoustic Emission Testing P ART 2. Acoustic Emission Monitoring of Crack Growth in Steel Bridge Components F IGURE 5. Bridge hanger dimensions and location of cracks. 13 1 2 3 4 5 6 7 8 9 175 mm (7 in.) 225 mm (9 in.) 610 mm (24 in.) 165 mm (6.5 in.) Legend 1. Crack 1. 2. Crack 2. 3. Crack 3. 4. Wideband transducer. 5, 6. Source location transducers. 7, 8, 9. Guard transducers.
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rubbing occurred throughout the load cycle. Acoustic emission activity from all three cracks were clearly identified and were classified as crack growth or noise signals using location, strain magnitude, position on strain cycle and uniqueness of waveforms as the primary criteria (Figs. 7). A vast majority of acoustic emission signals from the cracks were found to be caused by crack face rubbing and the crushing of corrosion products between the crack faces (Figs. 8 to 10) whereas limited crack growth emission was detected.
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  • Fall '19
  • The Land, Nondestructive testing, Acoustic Emission

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