Thin-ply composites, owing to their excellent damage resistance and mechanical strength, can significantly contribute to structural weight reduction. Additionally, they have the advantage of improving the design freedom in composite structures. In this study, the effects of the ply thickness and laminate layup on properties such as the damage resistance and mechanical strength in CFRP laminates with toughening interlayers were experimentally evaluated. Non-hole tensile (NHT), open-hole tensile (OHT), and filled-hole tensile (FHT) tests were conducted on CFRP laminates with various ply thicknesses and 0° layer ratios. The damage characteristics of laminates with toughening interlayers were investigated via damage observation using an optical microscope and soft X-ray inspection. The obtained damage resistance and mechanical strength were compared to those reported in previous studies conducted on specimens without a toughening interlayer. The correlation between the damage resistance obtained from NHT tests and mechanical strength obtained from OHT and FHT tests was discussed. The results showed that the toughening interlayer increased the OHT and FHT strengths, although the structure was more susceptible to cracks.
