Delamination Fracture Toughness of Graphite and Aramid Epoxy Composites

The delamination fracture toughness of graphite and aramid-epoxy composite laminates was determined as a function of loading rate for unidirectional and woven reinforcements. In addition, the in-situ fracture toughness of the epoxy matrix was obtained by determining the crack energy release rate during the delamination fracture of thin epoxy films. The fracture surfaces were investigated using scanning electron microscopy. The results show that increasing the loading rate and the use of woven reinforcements increase the fracture toughness. A model was used to estimate the relative contributions from the fiber-matrix interface and the matrix to the overall delamination crack energy release rate.