Abstract In this paper, barium ferrites (BFs) with an average particle size of 100 nanometers as filler are used to explore the improvement of the mechanical properties of casting polyurethane (CPU). The nano‐BFs‐filled CPU is prepared in situ by adding the suspension of nano‐BFs in DMF to polyurethane precursor. The dynamic mechanical analysis is carried out to investigate the viscoelastic properties of nano‐BFs‐filled polyurethane. It is found that the strain energy density (SED) and the hysteresis energy density (HED) of polyurethane composite increase significantly after adding nano‐BFs filler. For the filler content of 0.5 wt%, the SED and HED increase by 587% and 486% respectively, but the hysteresis loss for all of composites remains almost unchanged. The results of Payne effect study show that the storage modulus and the loss modulus of all nano‐BFs‐filled polyurethane composites are significantly higher than that of pure polymer. The storage modulus of 0.5 wt% nano‐BFs‐filled polyurethane is the highest. At 25°C, 1 Hz and strain of 10%, compared with pure polyurethane, the storage modulus of 0.5 wt% nano‐BFs‐filled polyurethane increases by 310%, while the loss modulus increases by only 116%. A small amount of nano‐BFs is sufficient to reduce the loss factor to 0.60 times that of pure polyurethane, which indicates that the material becomes more elastic after adding nano‐BFs. Our method can effectively coordinate the contradiction between strength and fatigue resistance of composites, significantly improving the energy storage modulus and reducing the loss factor while remaining the H index of hysteresis loss almost unchanged.
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