Abstract
Thin polyimide (PI) films have been widely used for spacecraft polymeric materials. However, small defects often initiate at the surface of PI films by the erosion of atomic oxygen present in space environment, especially in low earth orbit. Mechanical strengths of polyimide films are significantly reduced by these defects. To evaluate the material strength of PI films for space use, therefore, it is important to consider the crack propagation from the defect in the direction of film thickness. In this paper, tensile tests were carried out using PI films with a surface short crack and fracture processes from this short crack were observed by a color 3D laser scanning microscope. Based on the results, fracture toughnesses in the film thickness direction were estimated. The fracture toughness tests were carried out with two types of specimens having different pre-crack lengths, 20μm and 40μm. Fracture toughnesses of 20μm and 40μm pre-cracked specimens were about 12kJ/m^2 and 1.8kJ/m^2, respectively. These fracture toughnesses were compared with the data obtained by other researchers and the effectiveness of our data was discussed qualitatively.
