The environmental effects of water and jet fuel absorption on AS4/3501-6 graphite/epoxy were measured in terms of the changes in the interlaminar fracture toughness. Saturated double cantilever beam (DCB) and end notched flexure (ENF) specimens were tested to determine the environmental effects of moisture sorptions on critical strain energy release rates, GIc and GIIc, respectively. These data are compared with baseline data obtained for specimens tested in the room temperature dry (RTD) condition. This phase of the study revealed that moisture absorption of either water or jet fuel tends to toughen this material and that this change is more significant for Mode I than for Mode II.
This paper also presents the results of a fractographic analysis of the fracture surfaces developed in these unidirectional specimens. These results document the changes in the surface morphology due to the environmental conditions studied. Significant differences were observed for Mode I fracture surfaces. SEM fractographs of delamination surfaces for DCB specimens reveal that the moisture absorption condition results in fracture surfaces where the fibers are covered with resin. This corresponds to the Mode I toughening, which is quantified in terms of an increase in GIc. The differences in the fractographs of saturated and room temperature dry ENF specimens are less profound, with the hackle formation in the former case being more deformed than the latter.