7. NDE for Advanced Materials
The purpose of this study is to try to determine the current mechanical state of a composite specimen (or structure) and predict its remaining lifetime from the characteristics of the acoustic emission (AE) signals it emits under load. In previous studies of the characteristics of AE generated in graphite-epoxy composites, empirical observations were made relating the frequency content and the amplitude distributions of the AE signals to singular points on the loading curve of a specimen and to the composite's, moisture content. Up to now, these relationships have been difficult to study systematically because of limitations in efficiently handling the large amount of data contained in the emission signals. With the Acoustic Emission Multi-Parameter Analyzer (AEMPA) (developed under a Science Center IR&D program), pertinent information is abstracted from each emission signal as it occurs during a test and is stored in compact digital form for subsequent data processing. Multi-parameter correlation and pattern recognition techniques among the 23 abstracted parameters are then used to identify distinct types of AE events, and various observations used ,to 'identify the microscopic mechanisms of flaw growth in the material which generate these different'types. For those geometries and load conditions which product failure by a well defined series of mechanistic steps (e.g., matrix crazing, fiber-matrix interface debonding, fiber fracture, interlaminar fracture), it may be possible to predict specimen·failure by determining the relative amounts of the various mechanisms occurring at a given time in the life of the specimen from the AE signals. Progress along these lines using MPA is described.
Graham, Lloyd J., "Acoustic Emission in Composites Using MPA" (1979). Proceedings of the ARPA/AFML Review of Progress in Quantitative NDE, July 1977–June 1978. 50.