Fuzz ball defects in unidirectional carbon fibre-reinforced pultruded profiles: Numerical compressive strength predictions

Manufacturing-induced defects in fibre-reinforced polymers are an inherent challenge in manufacturing large structures, making it essential to understand their impact on structural performance and to define acceptable defect tolerances. This work addresses the issue by developing a finite element framework to characterise the compressive behaviour of composites with fibre misalignment defects. The method is demonstrated using a unidirectional carbon fibre-reinforced pultruded profile containing an embedded fuzz ball defect. Simulation results are validated against experimental four-point bending tests of sandwich beams. A compressive strength prediction model, closely resembling the experimental setup, was developed using realistic fibre distributions from micrographs and implementing them in a non-linear finite element model. All tested sandwich beams with fuzz ball defects exhibited compressive failure in the gauge section. Post-mortem microscopy revealed localised through-thickness kink band failure, which was used to identify a representative modelling plane for a 2D plane strain model. Predictions showed kink band failure in regions of severe fibre misalignments, consistent with experimental observations. The predicted compressive strain to failure was within 3% of the measured average. This 2D modelling approach demonstrates high accuracy in capturing the effects of manufacturing-induced defects and provides an efficient tool for assessing structural risks associated with fibre misalignment defects.