Impact Automated Fibre Placement Induced Defects on the Compression Behaviourof CFRP Structures

Process induced defects during automated fibre placement (AFP) have an impact on the mechanical behaviour of cured fibre composite structures. While recurring defects such as gaps and overlaps have been extensively studied, the impact of tow-twists and fuzzballs is not well known. Hence, this study presents the findings of compression tests carried out on carbon fibre-reinforced polymer test specimens with intentionally placed tow-twists and fuzzballs. The defects are characterised based on geometric data acquired during layup. The cured specimens are further examined by computer tomography, giving an unprecedented understanding of how the defects deform during curing and affect the neighbouring laminae. In addition, 3D meso-scale finite-element simulations of laminates containing the aforementioned defects are conducted using the geometric data from the tomograms. The simulation output is compared to the behaviour observed in the experimental tests. The results from the compression tests indicate an influence of the defects on the compression strength, compression stiffness and buckling behaviour of the laminate. A conclusion is drawn towards being able to accurately predict the mechanical impact of fuzzballs and tow-twists numerically, thus aiding in the decisionmaking of whether to remove such defects during parts production in the AFP process