Time-dependent Microcracking Detected in a Rubber-toughened Carbon-epoxy Composite by the Modal Acoustic Emission Method

Abstract

A method of modal acoustic emission monitoring and waveform analysis is developed as a means for tracking two of the primary damage mechanisms in unidirectional composite lamina, matrix-cracking and fiber–matrix debonding. Unidirectional 30, 45 and 90° coupons of a rubber-toughened carbon-epoxy are monitored in this way for various loading histories. A method of comparing waveforms from different samples is proposed in order to establish the similarity of microcracking regardless of fiber direction. Histograms of waveform energy are used as a measure of average arrested crack length versus stress level. Larger faster cracks will emit more energy. Finally, an interpretation of the AE data is given based on an initial population of existing flaws where a cumulative distribution function (CDF) of microcracking is defined and used to study effects of stress history.

Keywords

microcracking composite material modal acoustic emission damage viscoelasticity rubber-toughened

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