Abstract
The thin polyimide (PI) films have been widely used for the spacecraft polymeric material. However, small defects often initiate at the surface of PI films by the impingement of atomic oxygen present in the space environment such as 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 the fracture toughnesses in the film thickness direction were compared with the results of FEM numerical analyses. From the experimental results, R-curves of PI film were obtained using J-integral. These R-curves had a similar trend of R-curves obtained from the standard specimens. However, the fracture toughness measured by R-curves was about five times higher than the calculated value by the numerical analyses for each initial crack depth. The reason for this discrepancy was discussed based on the following two factors; one is a considerable plastic deformation at the tip of pre-crack introduced by a razor blade, and the other is an underestimation of crack extension Δa.
