Interlaminar Mode I crack growth energy release rate of carbon/carbon composites

The interlaminar Mode I crack propagation in a twill weave carbon/carbon composite was investigated using the double cantilever beam test. Interlaminar fracture occurred at the fibre–matrix interface between the plies and multiple small delaminations apart from the main crack were observed. Critical energy release rates were calculated using six different methods in order to evaluate their suitability to encounter the particular interlaminar properties of C/C composites. One method covered the integration of the load–displacement curve while the other methods considered the compliance of the cantilever arms also being subjected to deviations from the elementary beam theory. The modified compliance calibration method gives the most conservative estimation of the critical energy release rate, while the area integration method is also applicable to specimens with secondary cracks.