Influence of loading rate on the delamination response of untufted and tufted carbon epoxy non crimp fabric composites: Mode I

This research aims at the high speed Mode I delamination characterisation of carbon Non Crimp Fabric composites (NCF) with and without through the thickness reinforcement. The dynamic delamination response under Mode I is investigated using visual and force measurements as well as numerical analysis to minimize errors due to the dynamics of this test. For loading speed larger than 3 m/s the double cantilever beam (DCB) is subjected to mixed Mode loading (Mode I/II). This result is inherent to the nature of the test and the impactor that introduced the load in the lower DCB arm. Numerical simulations show that this effect would also occur for UD laminates. Consequently the validity of the tests is limited to loading speeds below 3 m/s until which pure Mode I loading is achieved. For those loading rates optical analysis shows rate effects only at the crack initiation state which are stronger for the tufted interface. To avoid mixed mode effects at higher loading rates (>3 m/s), the DCB specimen must be loaded at both arms simultaneously. Load cell recordings are not necessary as optical analysis is confirmed as a reliable technique for rate effect investigations.