Acoustic emission signal analysis

Abstract

An extension of acoustic emission technology was made which permits identification of probable source mechanisms for signals emitted during the failure of metals. This was achieved through the construction of a unique instrument and the development of special computer programs. The instrument permitted wideband digital waveform recordings to be made of both acoustic emission signals generated during the failure of a specimen, as well as calibration signals derived from a helium gas jet. These recordings were then processed by the computer programs to yield power spectra insensitive to specimen geometry, thus allowing the direct comparison of acoustic emissions from different specimens. A series of experiments conducted to test the instrument and the programs resulted in the conclusion that, at the 95% confidence level, acoustic emission caused by brittle particle fracture in 7039 aluminum could be differentiated from acoustic emission caused by the discontinuous movement of a crack in 4340 steel. Detailed descriptions of acoustic emission source modeling, transducer operating principles, calibration techniques and digital signal processing provide the necessary theoretical background for the reported technology extension, while a comprehensive review of the literature of acoustic emission places the experimental work into the proper context.