Acoustic Emission Behavior of Flawed Unidirectional Carbon Fiber-Epoxy Composites

Abstract

This paper reports an experimental investigation on mechanical and acoustic emission behavior of specially designed and manufactured carbon fiber epoxy composites. Uni directional composite laminates with various flaw configurations were tested in tension and their mechanical and acoustic emission responses were determined. Fiber fracture, delamination, splitting (or cracking along fibers) and friction of delaminated faces contrib uted to characteristic acoustic emission behavior. These can be discrimination on the basis of peak amplitude and event duration of observed acoustic emission signals.

The short duration ( < 100 μs), lower amplitude signals ( < 50 dB) signify carbon fiber fracture, while the medium amplitude signals (50 ∼ 70 dB) with an average event dura tion of —120 μs indicate the initiation and slow growth of delamination. High amplitude events ( > 70 dB) have long ( > 200 μs) event durations and are caused by rapid advances of delamination. Splitting or cracking along the fibers produces low to medium amplitude events with a long event duration ( > 100 μs). This type of acoustic emission signals has overlapping characteristics with those of delamination and needs further delineation of distinguishing parameters. Delaminated samples also emit acoustic emission signals with amplitudes in the range of 40 ∼ 50 dB and event duration of < 150 μs. These appear to arise from the friction of delaminated faces.

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