Structural damping using encapsulated shear thickening fluids

Smart structures with tunable damping and stiffness characteristics are of high interest to aerospace applications, but often require an external power source to be activated. This can be avoided by using highly concentrated silica suspensions, which exhibit a shear-thickening behavior, linked to a dramatic increase in viscous dissipation. These materials are however liquid at rest, and sensitive to humidity, so they are difficult to implement as such into structural applications. In the present work, highly concentrated solutions of monodisperse silica particles in PEG were selected for their strong thickening effect at rather low critical shear strain. Damping properties were characterized by measuring the energy dissipated per cycle at low frequency (<2Hz) during oscillatory tests using a rheometer. STF were impregnated in an open-cell foam scaffold and encapsulated into a RTV-silicone to produce patches that can be handled easily. Silicone also protects the STF against outgassing or humidity pickup. Experimental results show a simultaneous increase of stiffness and damping properties for theses patches at low frequencies and large strains. Damping is thus getting closer to the range of elastomeric commercial damping materials, possibly overtaking them in specific conditions.