On characterization and location of acoustic emission sources in real size composite structures: a waveform study

A series of pairs of acoustic emission (AE) waveforms taken from either a closely spaced pair (64 mm) or a widely spaced pair (410 mm) of AE sensors mounted on a spherical graphite/epoxy pressure vessel of 260 mm outside diameter were examined. The waveforms from the small (6.3 mm dia.) aperture non-resonant sensors bandpassed from 85 to 325 kHz were recorded simultaneously on a 12-bit waveform recorder. Changes due to wave propagation in the typical AE hit characteristics (peak amplitude, duration, energy, spectrum, etc.) were correlated with distances from source to sensors and physical principles of wave propagation. Based upon the results, implications for AE monitoring and future AE studies of large fiber/polymer composite structures are presented. Also, AE source location in conjunction with a model for localized failure of a large aerospace type fiber/ polymer composite structure was considered. Large changes in typical AE hit parameters were observed, particularly in the first 60 mm of propagation. These results bring into question typical approaches that have been developed for source identification and assessment of source significance in small test specimens. Large changes in arrival times of the same event at separate sensors were observed as a function of the system threshold setting. Possible approaches to overcome arrival time deficiencies as well as suggestions for future studies are presented.