The effect of surface cracks on tensile strength in polyimide films exposed to low earth orbit in MPAC&SEED experiment

Abstract

The surface textures of polyimide (PI) films exposed to a low Earth orbit environment in the “SM and JEM/MPAC&SEED experiments” and PI films irradiated by atomic oxygen (AO) using a ground facility were quantitatively evaluated. Additionally, the degradation in tensile strength of these PI films was assessed in terms of the surface texture changes. The exposed surfaces of the flight PI films were contaminated by silicon oxide layers and included some local valleys, or extremely deep depressions compared with the surrounding areas. The depth of the deepest local valleys on the exposed surfaces (a0max), which were predicted by extreme statistics, exceeded those of the local valleys of the AO-irradiated PI films. When the tensile strength of these PI films was plotted against AO fluence, the tensile strength reduction trends clearly differed for each PI film. However, the reduction trends were shown to closely correlate when the tensile strengths were plotted against a0max. These results mean that the tensile strength of the PI films attacked by AO can be evaluated based on the depth of surface cracks and that fracture mechanics is considered an effective tool to predict tensile strength reduction.