Abstract
Polyimide (PI) films have been applied to construction materials for space film structures such as flexible solar arrays and solar sails. In this research, mechanical properties degradation of PI films by atomic oxygen (AO) were experimentally evaluated with tensile tests and predicted with fracture mechanics methods. Then, the experimental values and the predicted ones were compared to confirm effectiveness of the fracture mechanics methods. AO is the main atmospheric components in a low earth orbital (LEO) environment and can erode polymer materials surfaces; polymer materials attached by AO exhibit a rough texture. Tensile strength of PI films irradiated by AO using a ground facility reduced concomitantly with increased AO fluence (FAQ). In the rupture of the PI films, cracks originated from the AO-irradiated surfaces which had rough textures because of AO erosion and grew unstably after a stable growth. The tensile strength of the PI films was calculated with fracture mechanics methods. Mirror regions observed on the fracture surfaces were considered to fracture defects and fracture toughness equations for a strip with a semi-elliptical surface crack were applied in the calculation. The predicted values almost corresponded with the experimental ones. Additionally, in the PI films exposed to the LEO environment, the tensile strength predicted with the fracture mechanics methods was comparable to the experimental data. These results indicated that this method is an effective tool for strength analysis of PI films exposed to a space environment.
