Initiation of failure at notches in unidirectional fiber composites

Abstract

A four point bend setup is used in observing compressive damage initiation in a unidirectional carbon/epoxy single edge notch beam. Damage initiation is observed in 8 specimens with a camera during testing and the test is stopped when damage occurs. Post observation of the polished specimens showed a micro buckling instability at the notch tip in 5 specimens and splitting in 3. The damage initiation is modeled as an individually discretized fiber and matrix 2D plane strain finite element model. To reduce calculation time, the superelement approach is used to model the whole beam except a small local area at the notch tip. A good agreement of the critical force is found between the analysis and the experiments with a deviation of 4%. A comparison is made with the compressive crack approach with a deviation of 9% on the critical energy release rate.