Influence of silica nanoparticle size and loading in shear thickening fluids on yarn pullout and inter-yarn friction of Kevlar fabrics

Aramid woven fabrics are widely used in flexible protective systems because of their high strength-to-weight ratio. Inter-yarn friction plays a critical role in controlling yarn mobility and energy redistribution under quasi-static and low-velocity loading conditions. In this study, shear thickening fluids containing silica nanoparticles with diameters ranging from 100 to 600 nm and mass loadings of 62–70 wt% were synthesized and applied to Kevlar ® 802F fabrics. Rheological analysis showed that decreasing particle size and increasing concentration reduced the critical shear rate while increasing peak viscosity. Yarn pullout experiments demonstrated that STF treatment significantly enhanced pullout resistance, with the maximum extraction force increasing from 20 N for neat fabric to 63.15 N for the 250 nm particle-treated fabric, corresponding to an improvement of about 215 %. Finite element simulations using ABAQUS were employed to inversely determine effective inter-yarn friction coefficients, which increased from 0.26 for neat fabric to 0.59 for optimized STF-treated specimens. Regression analysis revealed strong positive correlations between peak viscosity and pullout force (R 2 ≈ 0.89 for particle size variation and R 2 ≈ 0.92 for concentration variation). The estimated operative shear-rate range during yarn pullout (30–80 s −1 ) corresponds closely with the onset of shear thickening in optimized STF formulations.