Rheological and energy absorption characteristics of a concentrated shear thickening fluid at various temperatures

Shear thickening fluid (STF) material is a suspension with a certain amount of nano- or micro-particles dispersed into a liquid medium whose viscosity increases with the rate of shear strain. Due to its exceptional rate-dependent property, STF has been regarded as a promising energy absorption material with potential application in soft body-armour. This study examines the rheological, impact resistance and energy absorption characteristics of an STF with concentrated polymer submicron particles under various temperatures. The rheological testing was conducted using a rotational rheometer with a temperature-control hood at shear rates measured from 0.01 s(-1). The studies reveal that the shear thickening behaviour of the STF is temperature-dependent and the critical shear rate for the onset of shear thickening decreases with the reduction of temperature. In particular, shear thickening behaviour of the STF at 0 degrees C was observed with the formation of shear bands evolving into cracks on the free surface of the STF. Low-velocity impact tests were conducted using a drop-weight tower with a temperature-control chamber. The study shows that the impact resistance of the STF increases with the decrease in temperature. In particular, the impact resistance shows an early response time when the impact resistance slowly picks up, corresponding to mechanisms of jamming-associated "solidification" and propagation of front of the "solidified" region. A simple one-dimensional model is also adopted to comprehend the response time for effective energy absorption of the STF addressing the mechanisms, and the general agreement of the predicted response time with that from the experiments demonstrates the effectiveness of the model.