Investigation of the rheological characteristics of shear thickening fluids for potential applications in body armour

Abstract

The flow behaviour of shear thickening fluids (STFs) has recently been found to have significant practical use. STFs are now being utilised in the development of vehicle suspension and more importantly body armour. Conventional body armour typically only protects the 'high risk' areas of the body such as the head and chest. However, impregnating Kevlar with STF provides equivalent protection in a lighter and more versatile armour that could be used to protect the bodies extremities .Thus, the influence of shear stress, volume fraction of the colloidal particles, temperature, 'impulse' testing as well as a shear stress loop on two silica-glycerol dispersions (Aerosil 200 and 300), were investigated to provide a broad foundation for future work. A Bohlin CVO controlled stress rheometer was used to rheologically characterise the samples. Step testing from 1-600 Pa resulted in significantly lower viscosities for the Aerosil 200 sample. Increasing the volume fraction of the particles increased the degree of shear thickening. The effects of temperature on the viscosity of the STFs were found to follow the Arrhenius relationship. Shear thinning did not occur when STFs experienced sudden increases in shear rate during impulse testing. Thixotropy, evaluated using a shear stress loop, was observed at all volume fractions. Lastly, samples were tested with an increasing amplitude oscillatory shear stress (1-400 Pa, 1Hz). The results found the fluid to be less viscoelastic with increasing volume fraction, the complex modulus also increased with lower shear stress and at lower rates