Experimental study on the low-velocity impact and compression after impact performances of composite laminates with a surface protection layer

The low-velocity impact and compression after impact performances of composite laminates with a surface protection layer was experimentally investigated. Through drop-weight low-velocity impact tests, impact force histories, indentation depths and delamination areas inside the laminates were obtained. The damage tolerance performances for the groups of laminates can be evaluated through compression after impact tests. The test results show that the delamination initiation loads for the laminates with a surface protection layer are nearly the same with the bare laminates, while the impact energies required to generate an indentation with a depth of 1.0 mm are 24%-46% larger. Under the same impact energy, the C-scan delamination areas of the laminates with a surface protection layer are around 20%-50% smaller than the bare laminates. However, at the same indentation depth, the C-scan delamination areas do not change much when adding the surface protection layer to the laminates. The compression after impact (CAI) performances are in close relation to the delamination inside the laminates. Under the same impact energy, the CAI strength and failure strain are 15%-50% greater for the laminates with a surface protection layer which have smaller delamination areas compared with the bare laminates. At the same indentation depth, the CAI strength and failure strain do not appear to be much different for both the bare laminates and those with a surface protection layer.