Identifying unstable damage growth in CFRP composites under tension

This paper examines acoustic emission signals from composite specimens under tensile load. Specimens with and without prior impact damage were examined. Traditional acoustic emission parameters do not provide reliable indications of impending failure in these specimens. A dense array of sensor with frequency response extending over 2 MHz was used to monitor acoustic emission signals in this study. The onset of unstable damage in composite specimens was found to the be precipitated by the formation of groups of adjacent fiber breaks, termed multiplets, from microscopic and computed tomography examinations by researchers. The appearance of groups of near identical acoustic emission waveforms close to the final failure may be related to the formation of such multiplets. The size of such clusters of waveforms and their numbers when plotted as a function of load, appears to indicate the impending failure in both undamaged specimens as well as those specimens that were subjected to impact damage.