FATIGUE DELAMINATION OF A CARBON FABRIC-REINFORCED EPOXY COMPOSITE WITH CARBON NANOTUBES

Carbon fibre-reinforced epoxy composites are used in aerospace applications as primary aircraft structures where material fatigue can be an issue. Carbon nanotubes (CNTs) appear to enhance the fatigue resistance according to literature. This work presents the results of precise crack growth rate measurement on double cantilever beam (DCB) specimens made from a carbon fibre fabric-reinforced epoxy composite. Two plates were evaluated where the resin was enhanced using 0.5 % CNTs and a flame retardant for one of the plates. Loading in mode I was displacement controlled with R = 0.1, f = 4 Hz and a constant maximum strain energy release rate (G(I))(max) during the cycle. The value of (G(I))(max) was defined to be 20 % up to 60 % of the mode I interlaminar fracture toughness. The crack length was determined from the modified compliance calibration (MCC) method by video-recording the specimen edges. The specimens enhanced by CNTs had a significantly decreased fatigue crack growth rate by approximately 80 %. The crack growth rate was also observed to be related to the interface of the weft and warp tows of the plain weave. Interlaminar fracture features and agglomerated CNTs were observed using a scanning electron microscope. Delamination extension during fatigue was analytically modelled using the relation of the delamination growth rate to the maximum value of the strain energy release rate. The understanding of crack growth rate in carbon fabric reinforced composites is crucial, especially when adopting the damage tolerance philosophy for use in an aircraft structure.