Effect of fatigue loading on impact damage and buckling/post-buckling behaviors of stiffened composite panels under axial compression

Effect of fatigue loading on impact damage and buckling/post-buckling behaviors of stiffened composite panels under axial compression were studied in this paper. Barely visible impact damage (BVID) was introduced to stiffened composite panels. Damage areas and crater depths data were analyzed and their distributions were determined, whose upper limits were also calculated under different reliability. Then fatigue experiments were conducted on impact specimens. Damage areas, damage site shapes and crater depths were measured at every certain fatigue cycles. Compression after impact (CAI) as well as compression after impact and fatigue (CAIF) were also studied, with a comparison of virgin specimens. The results exhibited impact damage and the following fatigue loading had no obvious influence on the bucking load and buckling modes. Additionally, failure modes of all types of specimens were similar, which included debonding and fracture of stiffeners together with splitting and cracking of skin bays. However, the average failure load of impact specimens decreased 9.9% compared to that of virgin specimens. Fatigue loading would lead a further decrease about 6.1% in failure load compared to impact specimens, although the impact damage had no obvious changes during and after fatigue loading.