In the mid-1970's a program of fundamental research was initiated at NBS to improve the scientific understanding of acoustic emission. Many individual results of this research have been reported in the literature and are beginning to be incorporated in a new generation of acoustic emission instrumentation, in improved test methodologies, and in the analysis of data. Here, we summarize the problems faced by acoustic emission <{llidway through the last decade, review the accomplishments of the NBS program and related research programs, and outline the research that will be required in future years.

Acoustic emission waveforms for the epicentre location of an elastic half-space have been calculated for force dipoles and combinations of force dipoles representing the formation of point microcracks, the motion of dislocations and dilatation sources. The effects of source orientation, depth and time dependence are shown graphically. These results are used to emphasise the features of acoustic emission signals and their frequency spectra that must be accurately measured if dynamic information or the source type are to be deduced.

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