SynopsisA series of high-molecular weight condensation polyimides was evaluated to determine the effect of polymer molecular structure on the transmission rate of oxygen, carbon dioxide, and water vapor. The polyimide films were prepared from either 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) or pyromellitic dianhydride (PMDA) with various diamines. The study shows that molecular structure had a strong influence on gas transmission rates with results for some films varying three orders of magnitude from that of other polyimide films. In general, the BTDA series of polyimides had overall lower gas transmission rates than the PMDA-derived series. Polymers prepared with metu-oriented diamines characteristically displayed lower gas transmission than those prepared with para-oriented diamines.
This investigation of composite material properties utilized T300/934 graphite-epoxy that was subjected to 1.0 MeV electron radiation for a total dose of 1.0 x 1010 rads at a rate of 5.0 x 107 rads/hour, simulating a worst-case exposure equivalent to 30 years in space. Mechanical testing was performed on 4-ply unidirectional laminates over the temperature range of -250°F (116 K) to +250°F (394 K). In-plane elastic tensile and shear properties as well as strength were obtained ( E1, E2, v 12, G12, XT, YT, S). The results show that electron radiation degrades the epoxy matrix and produces products that volatilize at the temperatures considered. These degradation products plasticize the epoxy at elevated temperatures and embrittle it at low temperatures, thereby altering the mechanical properties of the composite.
Electron microscopy was used to analyze the fracture surfaces of T300/934 graphite/epoxy, unidirectional, off-axis tensile coupons which were subjected to 1.0 MeV electron radiation at a rate of 5.0 × 107 rad/h for a total dose of 1.0 × 1010 rad. Fracture surfaces from irradiated and nonirradiated specimens tested at 116 K (−250°F), room temperature, and 394 K (+250°F) were analyzed to assess the influence of radiation and temperature on the mode of failure and variations in constituent material as a function of environmental exposure. Micrographs of fracture surfaces indicate that irradiated specimens are more brittle than nonirradiated specimens at low temperatures. However, at elevated temperatures the irradiated specimens exhibit significantly more plasticity than nonirradiated specimens. The increased plasticity in irradiated specimens tested at elevated temperature is much more evident in 10° offaxis specimens. This is the result of the high shear stresses in these specimens. The same high degree of plasticity is not observed in the 90° specimens which fail at a much lower ultimate strain. Little difference in fracture surfaces and material behavior for irradiated and nonirradiated specimens is noted for room temperature specimens. The analysis of the photomicrographs is shown to correspond well with mechanical behavior of the specimen.
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