Study On Fatigur Delamination Of Laminated Composites With Pre-Crack

Delamination growth are common in laminated composites under cyclic loading. It's easy to be damaged below designed force and affect its use as main load-carrying component. So it's important in engineering to study the fatigue delamination performance under cyclic loading.First, optimize the preparation process, get unidirectional and laminated specimen with Teflon thin film between layers as pre-crack.Then interlaminar and static compression properties of unidirectional and laminated specimen are tested in order to make sure of the load displacement of local and global buckling. Compare the static compression properties of unidirectional and laminated specimen, it is found that the local and global buckling force of unidirectional specimen are higher than laminated specimen; while the local and global buckling load displacement of unidirectional specimen are lower than laminated specimen. It's because the axial modulus of unidirectional specimen are higher than laminated plates specimen.Determine the load displacement under cyclic loading based on the local and global buckling load displacement. It is found that a-N curve trend of specimen with same 25mm×25mm size, 1/10 depth Teflon thin film but different 0.5mm, 0.4mm, 0.3mm load displacement are the same. As the load displacement is increasing, the initial delamination is easier to occur, and the delamination length will be longer. And a-N curve trend of specimen with same 25mm×25mm size, 0.4mm load displacement but different 1/10, 2/10, 3/10 depth Teflon thin film are the same. As the depth of Teflon thin film is increasing, the initial delamination is easier to occur, and the delamination length will be longer. While a-N curve trend of specimen with same 1/10 depth, 0.4mm load displacement but different 15mm×25mm, 20mm×25mm, 25mm×25mm size Teflon thin film are the same. As the size of Teflon thin film is decreasing, the initial delamination is easier to occur, and the delamination length of the three sizes will be almost the same.Investigate the surface of delaminated specimen under cyclic loading with scanning electron microscopy. Microcrack, fiber breakage and matrix with compressive fatigue impression are observed.Through studies above, we can conclude use limits of fatigue delamination preliminarily in order to guide the preparation process of structure components and provide theory support in the use of composite plates as aeronautic material.