Relation of Acoustic Emission Signals to Microfailure Events

摘要

The Office of Advanced Research of the Federal Highway Administration issponsoring a research program aimed at enhancing the practical use of acoustic emission (AE) as an option for monitoring highway bridge integrity. SRI International is assisting the effort by attempting to develop a better understanding of the material microfailure events that produce acoustic signals. SRI's approach was to monitor AE in a laboratory fracture test, apply a quantitative fractographic technique, FRASTA, to identify microfailure events and the sequence in which they occur, and then to correlate microfailures with AE signals. Success would provide the ability to determine important characteristics of fracturing from the size and shape of the AE signals. This report describes the procedures and presents results from two initial studies, the first on a structural ceramic and the second on a weldment in bridge steel. Although a one-to-one correlation was not achieved for the ceramic, a route for identifying microfailure origins of acoustic emission was demonstrated. For the steel weldment, the early AE signals correlated with smooth faceted transgranular surfaces within a field of fine dimples, suggesting that acoustic signals are produced by brittle cleavage of certain grains in the steel microstructure. Future work will correlate microfailure in unwelded bridge steels with AE waveforms.