Thickening effect of shear thickening fluid under normal loading to improve stab resistance of shear thickening fluid-fabric composite

Shear thickening fluid (STF) for personal stab-resistant clothing has been consistently discussed. However, it is not clear whether STF in STF-fabric composite materials undergoes thickening under normal loads, and to what extent. In this study, the yarn pullout test and the knife-stab test in the quasistatic mode were used to establish the enhancement effect of STF, owing to the dominant thickening mechanism. The results of pullout-in tests for STF show that the thickening effort of STF becomes stronger with increasing speed. There is an observable increase for the pullout-in force. The addition of STF can slightly improve the yarn pullout force and peak stab force for STF-treated fabric at low velocities, owing to friction enhancement. More importantly, at higher speeds, the peak pullout force of yarn was increased to 28.9N, which increased by about 140% compared with low velocities. The peak stab forces increased by about 80% compared with low stab speeds. It is affirmed that the thickening effect of STF under normal loads plays a dominant role in enhancing STF-fabric composite materials.