Discontinuous Shear Thickening fluids such as cornstarch and water exhibit an amazing and useful response to impact. They become solid-like in response to impact and can, for example, stop an impacting object, or support a person running on the surface of the fluid, but remain fluid-like before and after impact. This project involves controlled laboratory experiments to study this impact response and aims to develop a better understanding of how jammed materials behave. The applications of this work include the design of materials for impact protection, as well as improved suspension flow processing. This research program includes the training and participation of graduate and undergraduate students in the scientific process. Outreach to local public school students includes lecture-demonstrations focusing on science and engineering education for women and underrepresented minorities.
The goal of this project is to understand the dynamic behavior of Discontinuous Shear Thickening fluids (including impact response and the ability to run on the surface). It has recently been found that a transiently jammed region of material can develop and propagate in front of an impacting object. The research team carries out experiments with a combination of force measurements and images of the jammed region at the surface to determine if and how the stress response correlates with the jammed fronts reaching the boundaries. The experiments investigate the physical mechanism behind the strong stress response by testing if the stress response scales with the stiffness of the boundary or particles as in other jammed systems. The research team also carries out experiments to determine the critical shear rate at the shear thickening transition under impact. This is tested with impact experiments for different impact velocities and fluid viscosities. A constitutive relation describing the dynamic behavior of Discontinuous Shear Thickening fluids can be developed from these experiments. The experiments are complimented by low-dimensional modeling to connect and explain the various dynamic behaviors of Discontinuous Shear Thickening fluids. This low-dimensional model requires as input a stiffness and relaxation times, obtained from measurements of the model system of impact experiments.
