Abstract
Background:The increasing use of composite structures with a high stiffness-to-weight ratio in commercial vehicles has brought about a reduction in fuel consumption but, on the other hand, has significantly increased noise transmission particularly in case of thin and lightweight structures. Noise is a primary issue for commercial vehicles, such as airplanes, helicopters and cars. The present research deals with the use of smart materials, as Shear-Thickening Fluids (STF, or dilatants) in view of manufacturing elements with increased sound insulation properties.Methods:The response of a sandwich material with the STF core was investigated both experimentally and numerically, by choosing the Sound Transmission Loss (STL) of the composite structure as the figure of merit.The experimental investigation was focused on the manufacturing of a sandwich structure made of metallic skins and a STF core that was successively characterized by sound insertion loss measurement.The numerical investigation was carried out by using a Generalized Transfer Matrix Method (GTMM) and a Statistical Energy Analysis (SEA) in view of selecting the fluid capable of granting the highest acoustic transmission loss.Results:Finally, the test results were compared to the numerical results, showing a noticeable agreement. The used STF showed increasing viscosity at increasing shear rates.
Highlights
The use of shear thickening fluids (STFs or dilatants) in Stab-resistant and impact absorbing applications has been thoroughly studied in recent years [1]
Previous works show that the calculation of the discrete relaxation spectrum can be used to evaluate the shear moduli outside of the regular frequency range taken into account in the rheological tests
The fc for a wt higher than 22 overcomes the upper bound of maximum sensitivity band of the human ear (i.e. 2000 Hz-4000 Hz) [28] and even though the Sound Transmission Loss (STL) reduction is higher, this does not remarkably affect the end-user
Summary
The use of shear thickening fluids (STFs or dilatants) in Stab-resistant and impact absorbing applications has been thoroughly studied in recent years [1]. These Non-Newtonian fluids present an abrupt increase in the apparent viscosity with the imposed shear rate and can be successfully used for the manufacturing of passive smart materials, advanced composite systems capable of altering their constitutive law basing on the applied stress/strain field. From a Vibroacoustic perspective, for coupons with increased sound insulation capabilities, the peculiar vibration dampening properties of STFs can be best employed by recurring to sandwich structures in constrained layer damping configuration (CLD), where the STF is interposed as the core of the sandwich structure and the outer skins are made of a much stiffer material, such as Aluminum. The present research deals with the use of smart materials, as Shear-Thickening Fluids (STF, or dilatants) in view of manufacturing elements with increased sound insulation properties
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