Paper number 778


C. M. L. Wu1, S. L. Bai2, R. K. Y. Li1, and Y. W. Mai3

1Department of Physics and Materials Science, City University of Hong Kong
83 Tat Chee Avenue, Hong Kong SAR, P.R. China.
2Department of Mechanics and Engineering Science, Peking University
Beijing 100871, P.R. China
3Center for Advanced Materials Technology, University of Sydney,
Sydney, NSW2006, Australia

Summary In the present study, an epoxy beam embedded with two single carbon fibers was made to study the fiber fragmentation behaviour in composites. The bending of the beam provides tensile or compressive loads of the same magnitude to each fiber. The transparent epoxy matrix allowed "on-line" inspection of the fibre during the bend test using a microscope. Birefringent patterns were obtained to reflect the stress state at different regions along the fibre, in particular, at or near fibre breakage regions. It was found that under a given bending stress, the fiber fragment under compression is shorter than that under tension, due to the fact that the compressive strength is lower than the tensile strength of carbon fibers. Interfacial shear strength was calculated with Kelly-Tyson's model for the fiber under compression and was found to be smaller than that under tension. The inversion of Poisson's ration effect was suggested to be the main reason for the difference, with the support from the different birefringent patterns obtained.
Keywords twin-fibre, single fibre, fragmentation, residual stress, tension and compression, birefringent patterns.

Theme : Interface and Interphase ; Mechanical Properties

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