Influence of interface waviness on delamination characteristics and correlation of through-thickness tensile failure with mode I energy release rates in carbon fibre textile composites

The delamination initiation and propagation behaviour of layer-wise 3D-textile reinforced carbon fibre/epoxy composites is investigated by through-thickness (TT) tension tests as well as Double Cantilever Beam (DCB) and End-Notch Flexure (ENF) experiments. Different standardised approaches to determine modes I and II strain energy release rates are applied and compared. The results clearly indicate a dependency of the delamination propagation characteristics on the propagation direction, induced by the textile architecture and the according interface waviness. In situ and ex situ computed tomography (CT) is used to investigate TT tensile failure characteristics. The statistical distribution has been investigated considering Gauss and Weibull approaches. A correlation is drawn between the mode I energy release rate derived from the TT testing and traditionally determined values based on DCB testing.