Residual flexural properties of surface scratched CFRP laminates with diverse span lengths and thickness profiles

Surface scratches represent a common defect encountered in the operation of carbon fiber reinforced polymer (CFRP) composite structures. However, predicting the residual flexural properties of scratched CFRP structures remains an engineering challenge, as shallow scratches (20–100 μm) can induce varied effects on CFRP structures contingent upon their sizes and geometries. To investigate the issue, comprehensive flexural tests using 150 notched CFRP laminate specimens with diverse span lengths and thicknesses were performed in this study. For experimental analysis, a closed-form model for determining the bulk tensile strength and fracture toughness of heterogeneous composites has been adopted and modified. It highlights that the ply thickness of CFRP plays a pivotal role in governing its (brittle or quasi-brittle) failure behavior and thereby should be considered as a microstructural parameter in the modeling. Based on that, the strength results from different test groups exhibit good consistency, shedding light on the key interactions between crack growth and specimen thickness, as well as between crack growth and specimen deformation (influenced by span-to-thickness ratio). These findings hold promises for aiding engineers in evaluating non-standard CFRP structures and in calculating the residual capacity of damaged CFRP structures.