The object of this study is to investigate the interlaminar fracture characteristics of a Gr/Ep composite material (HFG Gr/Ep) under the opening, shearing and mixed mode conditions and the effects on the interlaminar fracture toughness according to the fiber orientations on the crack surface [0/0], [0/30], [0/45] and [0/60].
The interlaminar fracture toughness was tested using antisymmetric test fixture proposed by M. Arcan, which is modified to accomodate the composite specimen containing an embedded interlaminar crack.
Both critical stress intensity factors and critical energy release rates were determined and 3 mixed mode fracture criteria were compared to experimental data.
Finally, the fracture surfaces of the test specimens were investigated by means of scanning-electron microscope (SEM), which could be observed the phenomena of the hackles, microcracks of matrix, fiber breakages and branching of the microcracks, etc.
The fracture toughness for the [0/0] case was found to be 0.657 $MPa\sqrt{m}$(36.5 J/$m^2$) and 3.851 $MPa\sqrt{m}$ (328.8 J/$m^2$) for the opening and shearing modes, respectively. Therefore the energy required for crack growth in mode II ($G_{I_c}$) was found to be 9 times that required in mode I ($G_{II_c}$).
For the other fiber orientations on the crack surface [0/30], [0/45] and [0/60], the fracture toughnesses were shown to be virtually independent of the fiber orientations on the crack surface and for the [0/0] case, it was slightly higher than the other cases, due primarily to fiber bridging effects.
The mixed mode test results showed fair agreements with the mixed mode fracture criteria.
