Recent advances in understanding of acoustic emission from fiber composites and metals

Abstract

The time and frequency domains of acoustic emission signals generated during loading of Kevlar 49/epoxy composites have been studied. The effects of composite thickness, transducer type, and load level have been examined. Results indicate that relatively low frequencies predominate. A study of the frequency spectrum of acoustic emission signals generated during fatigue testing of fracture toughness specimens has been completed. In particular, the dependence of frequency on the stress intensity level was studied. Extensive tension and compression testing of unflawed 7075 and 2124 aluminum has been undertaken. Among the results are (i) a correlation between fracture toughness and the acoustic emission generated during a compression test of 2124-T851; (ii) the rate of acoustic emission energy sensed at strains greater than 1.5% is more than two orders of magnitude greater in tension than in compression; and (iii) acoustic emission can easily be used to sort out plates of 7075 aluminum which have undesired 20–60-μm inclusion particles. [This work was performed under the auspices of the U.S. Energy Research and Development Administration, under contract No. W-7405-Eng-48.]