Edge Effect on Unidirectional Composite Observed During Acoustic Emission Monitoring

• Published in: Journal of materials science letters 1992-01, Vol.11 (2), p.63-66
• Main Authors: Petitpas, E, Valentin, D
• Format: Article
• Language: English
• ISSN: 0261-8028

The acoustic emission (AE) activity (number of ring down counts) was compared with the number of fiber breakages on a unidirectional carbon fiber reinforced polymer composite uniaxially loaded. The number of fiber breakages were counted on the edge of the sample after careful polishing and using a replica technique at several levels. The same samples were also examined using micrographic observation after the test had been stopped. Damage accumulation was monitored with an AE system using a piezoelectric transducer with a resonance frequency of 200 kHz. Clear evidence was found for random single fiber failure in most of the samples. Multiple fracture groups consisting of two or three adjacent broken fibers appeared at the end of the tests in regions where the fiber density is important. The fiber threshold was found to coincide well with the AE threshold and the two phenomena progressed in the same way. The damage threshold was approx 42% and the mean strength was reproducible. It was deduced that the AE comes from the fiber rupture. The results indicated that the edge effect can exist at a microscopic level on carefully prepared unidirectional C fiber reinforced composites. The results could also be analyzed using the Rosen model, giving information of both the intrinsic ineffective length of the fiber and the Weibull statistic describing the distribution in strength of the fiber inside the specimen.