Multiscale investigation of winding tension on porosity, misalignment, and mechanical performance of filament-wound CFRP composites

The quality and performance of filament-wound composite structures are significantly influenced by winding parameters, particularly the applied winding tension. Winding tension affects resin flow, porosity formation, fiber alignment, and ultimately the mechanical performance of the composite product. This study investigates the effects of winding tension on the structural integrity of carbon fiber-reinforced polymer composites and identifies the root causes of performance variations. A multiscale approach combining analytical, numerical, and experimental methods is employed. Analytical models describe the relationships between winding tension, resin flow, void growth, residual stress, and fiber bed compaction. Numerical simulations using representative volume element capture the microstructural effects of tension on fiber misalignment (with even a 7.12° fiber misalignment can reduce tensile strength by up to 20 %) and porosity, as well as their influence on stress distribution and overall mechanical behavior. Experimental investigations, including quasi-static tensile testing, X-ray tomography, optical microscopy, and fractography, are conducted to validate the models and examine damage mechanisms. The results reveal that increasing winding tension up to 25 N improves fiber alignment and reduces porosity, thereby enhancing the strength of composite. However, tensions beyond this level lead to higher residual stresses and lower mechanical performance due to fiber damage and incomplete resin infiltration. The study identifies 25 N as the optimal additional winding tension, achieving a porosity of 5.54 % with improved structural performance. These findings contribute to better understanding of process–structure relationships and provide guidance for optimizing the manufacturing of high-performance filament-wound composite structures, such as composite pressure vessels.