Abstract
The fracture toughness of graphite fibre reinforced unidirectional composite in mode II has been determined using a thin tubular specimen, by the method developed by Giare and Campbell, accepted for publication in Engng Fracture Mech. The crack growth resistance at instability and the corresponding initial strain energy release rates were independent of the initial crack in the range of the crack length investigated. G IIC obtained by thin tubular torsion specimen is 42% greater as compared to end-cracked beam method. The end-cracked beam method underestimated the G IIC as reported by J. W. Gillespie Jr, L. A. Carlson and R. B. Pipes [ Compos. Sci. Technol. 27, 177–197 (1986)]. They presented a finite element analysis of the End-Notched Flexure test specimen for mode II interlaminar fracture testing of composite materials. They predicted, using finite elements, that data reduction schemes based upon beam theory underestimate G IIC by approximately 20–40% for typical graphite fibre composite test specimen. It is very encouraging that our results follow very close to their prediction. It is concluded that the thin tubular torsion specimen method is accurate as compared to the end cracked beam method. G IIC of graphite fibre reinforced epoxy composite is found to be half of the glass fibre reinforced/epoxy composites, for practically the same V t of fibres.
Published Version
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