Thin tow-based discontinuous composites: Notched performance and energy absorption

Tow-Based Discontinuous Composites (TBDCs) are a new class of composite materials that have gained significant popularity.[1]. These materials are manufactured by chopping continuous prepreg tapes and randomly distributing them. The use of thin tapes minimises the scrap and waste material, brings down the price and manufacturing time and increases the overall sustainability of the material. In addition, the random tape distribution generates in-plane isotropy while the use of very low tape thicknesses (below 50 μm) also has beneficial effects. At first, the attainable fibre volume fraction is increased [2] while the damage mechanism is also shifted, effectively eliminating transverse tape fracture and promoting tape pull-out instead [3]. Optimised manufacturing methods have led to outstanding material properties which not only exceed any other value reported in the literature for discontinuous composites but directly compete and in some cases outperform conventional continuous composites. Such results have been reported under tensile [3], compressive [4], and fatigue loads [5]. Ongoing work is related to the characterisation of the material response under more complex loading scenarios such as the performance in the presence of notches and the energy absorption during tearing fracture. Open Hole Tension (OHT) testing was employed to evaluate the notched performance of TBDCs. Different notch sizes were evaluated (6, 9, 12 mm) and Digital Image Correlation (DIC) was used for the full-field strain resolution. The tests aimed to explore the notch sensitivity of thin TBDCs as contradicting studies were found in the literature reporting perfectly brittle or ductile responses. As shown in Figure 1, all specimens failed in the notch due to stress concentrations. The response was neither strictly brittle (notch sensitive) nor ductile (notch insensitive). Instead, the thin TBDCs displayed an intermediate behaviour, following closely the notched performance of QI laminates and contradicting previous studies on discontinuous composites.