Compressive allowables of composite laminates subjected to low-velocity impact

In order to evaluate the compressive allowables of composite laminates made from two types of carbon fiber/epoxy composite laminates with the fiber of T300 and T800, which are commonly used in aeronautical structures, low-velocity impact and compressive after impact tests were carried out for composite laminates made from the two composite systems with different thicknesses and stacking sequences. The relationships between impact energy, dent depth, damage area and residual compression strength etc were discussed, and the effects of thickness, stacking sequence, surface protection etc were also investigated. The condition for the barely visible impact damage (BVID) formation and the residual strengths of the composite laminates containing BVID were specially concerned. The results show that the laminate thickness and stacking sequence can affect the dent depth-impact energy relationship greatly, while their influences on the compressive strength after impact-dent depth and compressive failure after impact strain-dent depth relationships are much smaller. In the condition of the same layup proportion, impact energy for the BVID formation increases linearly with the laminate thickness. The performances of laminates with different materials vary that the X850 laminates have a better impact damage resistance than the CCF300/5228 laminates, but their damage tolerance performances are similar. Surface treatment such as adding the bronze and painting, can enhance the impact damage resistance of the laminates greatly, while it has little influence on the damage tolerance performances. The compressive failure strain of all the CCF300/5228 samples are more than 4 000 με, while they are more than 3 000 με for X850 samples, when the damage is not more than BVID.