Influence of loading rate on the delamination response of untufted and tufted carbon epoxy non-crimp fabric composites/Mode II

This research investigates dynamic delamination Mode II of carbon Non-Crimp Fabric (NCF) epoxy composites. Tufted and untufted configurations are considered. In order to achieve dynamic Mode II loading a modified end loaded split apparatus (ELS) is mounted on a drop weight impact tower. The high speed events are monitored through load recording and high speed image acquisition. Optical analysis of crack length and displacement combined with specimen geometry information and flexural properties allows the calculation of the delamination force and dynamic strain energy release rate in Mode II (GIIC). The untufted specimens show unstable failure once damage is initiated. Tufts are beneficial on the dynamic Mode II response as they increased energy absorption considerably and reduced the crack speed significantly. GIIC for the tufted composites is slightly positively dependent on the ELS specimen loading velocity. Optical analysis proves to be a reliable means to achieve high speed Mode II characterisation, whereas load signals are not sufficiently accurate to provide enough information for possible rate effects detection.