Synchrotron micro-CT in kink-band formation of UD-CFRP laminates with microdefects

This paper presents the first synchrotron micro-Computed Tomography (micro-CT) study on in-situ pure compressive kink-band failure in Uni-Directional Carbon Fibre-Reinforced Polymer composites (UD-CFRPs) with a notch. The study compares the failure behaviour of baseline samples under standard conditions with defect-rich samples containing micro-defects such as voids and fibre misalignment. Quantitative image-based analysis using the structure tensor technique and Digital Volume Correlation (DVC) reveals changes in fibre orientation and localised strain, respectively, at each increment load. A large 400 μm kink-band inclined at 30° with a half-cosine wave fibre orientation is observed in the baseline samples, while the defect-rich samples form narrower conjugate kink bands (ranging from 77 μm 25 μm) inclined at 45°. Development of kink-band formations/failure of both samples is discussed and compared with literature, providing key implications for the design and safe use of this type of composite layup.