The effect of resin toughness on the delamination fracture behavior of graphite/epoxy composites

Abstract

The objective of this dissertation research was to develop improved understanding of the deformation and fracture physics of delamination in resin toughened graphite/epoxy composites. Experiments were conducted in pure mode I, mixed mode I/mode II and pure mode II conditions. A damage dependent J-integral analysis developed by Schapery was shown to have merit in analyzing results from off-axis laminates. Using this analysis there appears to be an intrinsic delamination fracture toughness for mode I, independent of the fiber orientation or macroscopic modulus of the material. Rubber particle additions to the resin increase the mode I delamination fracture toughness more than they do the mode II delamination toughness. There appears to be a direct correlation between the size of the microcracked crack tip damage zone and the mode I delamination fracture toughness. Analysis of the fractured surface in an S.E.M. can be used to indicate the state of stress but not the crack growth direction.