Fatigue performance and damage characterisation of ultra-thin tow-based discontinuous tape composites

Tow-cased discontinuous composites are an attractive alternative material to conventional continuous composites as they offer in-plane isotropy, enhanced manufacturability allowing to achieve complex 3D shapes with high curvatures and local reinforcement in critical areas, while also maintaining high strength and stiffness, therefore expanding the design space significantly. In addition, the use of ultra-thin tapes and optimised manufacturing methods can increase the mechanical properties even further and change the damage mechanisms. Fatigue, however, could be a limiting design factor, as the fatigue behaviour of these materials has not been fully characterised. This work presents a complete study on the fatigue response of ultra-thin tow-based discontinuous composites: fatigue S-N curves are measured, and the damage and failure mechanisms are characterised utilising optical and scanning electron microscopy. Finally, a critical interpretation of the results is also presented by comparing the performance of ultra-thin tow-based discontinuous composites against other similar fibre reinforced composites and metals. It is shown that the optimised manufacturing methods combined with low tape thickness leads to enhanced quasi-isotropic fatigue performance. In addition, the fatigue limit was raised significantly compared to other discontinuous composites, and the tow-based discontinuous composites outperformed their metal counterparts when the results were normalised with density.