Mechanical performance of carbon-fibre- and glass-fibre-reinforced epoxy I-beams: I. Mechanical behaviour

This paper is the first in a series which detail the mechanical behaviour, finite element predictions and fractographic observations of the failure of composite I-beams. Experimental investigations into the behaviour under static load of both unnotched and web- and flange-notched continuously reinforced carbon-fibre/epoxy and glass-fibre/epoxy I-beams are discussed. A four-point flexural configuration is used. The global static response and ultimate failure are described in terms of strains, compliance, buckling and final fracture. A mode of buckling that is antisymmetric across the width of the compressive flange is observed prior to failure in all cases. Failure of the unnotched I-beams is concentrated around a buckle on the compressive flange whilst failure of the notched I-beams initiates from a shear-loaded circular cutout within the web. Buckling of the unnotched beams occurs at loads that are approximately 50% of the failure loads. Failure of the notched beams occurs at loads that are approximately 75% of the failure loads of the unnotched beams. Buckling and failure of the glass/epoxy beams occur at loads that are approximately 75% of the corresponding loads in the carbon/epoxy beams.