Influence of the crack plane asymmetry over GII results in carbon epoxy ENF specimens

In this paper unidirectional carbon epoxy End Notch Flexure samples (ENF) with different crack plane positions have been analyzed in order to study the influence of the degree of asymmetry over the load state at the crack tip. This study has been performed from different points of view: experimental, numerical approaches (Finite Element Models) and fractographic observations. From these studies it has been concluded that the deviation of the crack plane from the specimen midplane has no influence or little influence over the corresponding critical value of the energy release rate in mode II (GII). In other words, the asymmetry of the crack plane does not induce mode I load state at the crack tip while the energy release rate related to the mode II load remains almost constant as the crack plane moves from the midplane. Fractographic observations have shown “hackle markings” structures typical from mode II fracture. Finally, a good agreement was found between experimental and numerical procedures as errors were always lower than 7%.