The influence of novel 3D shear thickening fluid reinforcements in the mechanical behavior of hybrid composites under impact loading

Abstract Cork composites and shear thickening fluids (STFs) have been investigated for applications from ballistic protection to personal protective equipment. Cork-STF structures have also been developed, mainly based on cork-layered structures interfacially reinforced with STF. The STF interface improves impact mitigation, but usually marginally. This work explores the effect of 3D STF reinforcements in cork-based hybrid composites for enhanced impact mitigation. The composite structures consist of adhesively bound cork composite layers containing an STF reinforcement. The variables were the STF reinforcement’s depth, area, and shape (circular and hexagonal). The samples were subjected to 10 J impacts. The impact force reduction obtained with the 3D STF structures was significant. This was verified even for 2 mm-thick STF reinforcements, achieving an average reduction of 20.3% compared to neat cork. The 30 mm cylindrical reinforcement with a 5 mm depth achieved the highest impact force reduction of 59.7%. The hexagonal-shaped reinforcement with a 16.5 mm side length achieved a 57.5% impact force reduction for the same area. Another finding was the 25% optimum ratio between reinforcement depth and sample thickness. Although higher ratios imply higher STF volume, the optimum threshold was 25%. Overall, 3D STF reinforcement in composite structures demonstrates excellent potential for protective structures. Graphical abstract