Emission Behavior of Flawed Unidirectional Carbon Fiber - Epoxy Composites

摘要

This paper reports an experimental investigation on mechanical and acoustic emission behavior of specially designed and manufactured carbon fiber epoxy composites. Unidirectional 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 contributed to characteristic acoustic emission behavior. These can be discriminated on the basis of peak amplitude and event duration of observed acoustic emission signals. The short duration (<100 microseconds), lower amplitude signals (<50 dB) signify carbon fiber fracture, while the medium amplitude signals (50 - 70 dB) with an average event duration of approx. 120 microseconds indicate the initiation and slow growth of delamination. High amplitude vents (>70 dB) have long (>200 microseconds) 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 microseconds). 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 amplitude in the range of 40 approx. 50 dB and event duration of <150 microseconds. These appear to arise from the friction of delaminated faces.