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 28.9 N, 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.