Compression after impact behavior of flat and tapered Single-Double carbon composite specimens

Abstract

This research investigates the damage tolerance with compression after impact (CAI) testing procedure of five sets of specimens, that were manufactured using the card-sliding technique with non-crimp fabrics (NCFs) and adopting a Single-Double (SD) stacking sequence. Before undergoing CAI tests, initial damage was generated in the specimens with low-velocity impacts. Two sets of specimens are flat with a constant cross-section and they are manufactured with $\pm 45°$ and $\pm 30°$ NCFs, respectively. Two sets feature a tapered cross-section and the same NCFs as the flat ones, and the fifth set consists of tapered specimens with the same fiber orientation as one of the tapered sets but feature NCFs with different areal density. The CAI tests were performed according to the ASTM standard, using an infra-red camera and a digital image correlation system to record the thermal transient and the displacement of the specimens. Finite Element Analyses are validated and compared with the experimental results. The failure modes are discussed focusing on the various damage mechanisms, highlighting the effect of the tapered cross-section, the different NCFs, and the stacking sequence. This research provided insights on NCFs composite damage tolerance after low-velocity impact damage, highlighting the effect of adopting the novel SD stacking sequence and card-sliding method to taper the laminate. The analysis underscores the possibility to develop composites mitigating delamination risks and promoting intra-laminar damage.