Rheological behaviour of shear thickening fluids and their protection application

Non-Newtonian fluids do not follow Isaac Newton’s law of viscosity or constant fluid viscosity independent of stress applied to them. In non-Newtonian fluids, viscosity can change when force is applied so they become more liquid or more solid. Fluids that experience an increase in viscosity when a shear force is applied are commonly known as shear thickening fluids (STF). For the last 40 years, STFs have been studied extensively and they have created huge attention due to their very large potential for commercial applications. This study gave special consideration to their applications in protective body armour and personal protective equipment. The fabrication process, materials and rheological properties were collected and analysed for the STF produced in a laboratory. These experiments were conducted based on the previous research work done world-wide in this area, with a constant drive and efforts to develop new and better performance characteristics, which could benefit future applications. Three types of STFs were synthesised, namely standard STF made from fumed silica mixed with ethylene glycol carrier fluid, magnetorheological shear thickening fluid (MRSTF) made with the inclusion of carbonyl iron particles with the previously manufactured STF and shear thickening gel (STG) made from mixing boric acid, dimethyl silicone oil, ethanol and benzoyl peroxide. All of the above STFs were fabricated from predefined recipes and their rheological properties were measured with a rheometer under extensive rotational steady state and dynamic amplitude and frequency sweep testing experiments. Data was collected and analysed. Magnetorheological properties of MRSTFs were examined and correlated for different magnetic fields and different contents of carbonyl iron particles using the same rheometer, with the inclusion of the MCR Magneto-Rheological device unit. Special attention was given to the assessment of the performance of the current conventional Protective Body Armours (PBA), measuring their strengths and weaknesses. Current research indicates that the inclusion of STGs into manufacturing novel protective body armour could lead to achieving even better protective ballistic impact improvements and improvements in the flexibility and weight of the novel armour. Extensive lab testing experiments were conducted to validate this STF application. All of the experimental testing had to be limited to laboratory conditions but nevertheless, they clearly showed that usage of shear thickening fluids can significantly improve the ballistic protection of the garments used while at the same time reducing the weight and increasing the flexibility. Also, a significant effort within this study was to evaluate and assess the rheological performances of STFs in subzero temperatures. This was achieved using the Electro-Rheological Device (ERD) with achieved temperatures in testing down to -20 ͦ𝐶𝐶. Finally the ultimate aim of this study is expected to be the production of novel PBA impregnated with STG and would optimise its performance on ballistic protection.