Fracture Surface Characterization of Commercial Graphite/Epoxy Systems

The fracture surface morphologies of graphite/epoxy composite materials have been studied to determine the influences of load history, material configuration, temperature, moisture and matrix system type. Three commercially available systems with unidirectional tapes loaded in tension and fabrics tested in shear were chosen for analysis. Elevated temperature, moisture exposure, or both increase the amount of fiber pullout in the unidirectional tapes. Only in one case was the pullout fracture mode changed from a cohesive to an adhesive type of fracture process. The shear-loaded fabrics displayed either a tensile flexure fracture or an apparent shear fracture mode. The latter mode was believed to be actually a tensile rupture mode due to a resolution of shear stresses into tensile stresses. A transition temperature was defined to denote the temperature at which the fracture mode changed from tensile flexure to apparent shear. Significant differences in fracture surface morphology were observed among the three commercial graphite/epoxy systems.