Fractographic study of static and fatigue failures in polymer composites

A fractographic study of delamination failures in a range of carbon fibre and glass fibre reinforced plastics has been performed. Mode I (peel), mode II (shear), and mixed mode (I + II) interlaminar fracture surfaces, generated both statically and in fatigue, were examined. Intralaminar shear failures generated using a notched tension specimen were also studied. Fractographic features, including striations and matrix rollers, unique to fatigue failure, were identified on many of the mode II dominated specimens. As the mode I component of fracture was increased both the matrix rollers and striations were seen to diminish. While the features identified on the fatigue fracture surfaces enabled static fractures to be differentiated from fatigue failures, studies have shown that the use of these features for the determination of crack propagation directions and crack growth rates may be more limited. It appears that local variations in the stress state over the fracure surface tend to produce significant variations in their spacing and appearance. PRC/1581. (C) 1999 British Crown Copyright.