Recently, the authors have reported an exceptional normal incidence sound transmission loss characteristic for a class of low density, highly porous, and mechanically strong polyurea aerogels. Herein, a laminated composite comprising the organic low-density aerogels bonded with an inorganic compound (e.g., gypsum materials) is considered to investigate the constrained damping effects of the aerogels on the airborne sound insulation behavior of the composite using the standard chamber-based diffuse sound field measurements. Huge improvement in the sound transmission loss is obtained due to the use of aerogel without a significant increase in the overall weight and thickness of the composite panel (e.g., more than 10 dB increase by reaching 40 dB sound transmission loss at 2 kHz after the implementation of only two 5 mm-thick aerogel layers at bulk densities 0.15 and 0.25 g cm À3 ). This uncommon behavior breaks the empirical "Mass Law" nature of the most conventional acoustic materials. In addition, an exact analytical time-harmonic plane-strain solution for the diffused wave propagation through the multilayered structure is provided using theories of linear elasticity and Biot's dynamic poroelasticity. The theoretical results are well supported by the experiments which can be utilized for the design of the future light-weight multifunctional composite structures.
Low-density highly porous solid monolithic macroscopic objects, consisting of hierarchical mesoporous three-dimensional assemblies of nanoparticles (aerogels), have been previously pursued mainly for their low thermal conductivity. Unlike classical aerogels based on silica being fragile materials, structural fragility issue has been addressed with materials referred to as polymer-crosslinked (or X-) aerogels. X-aerogels are low-density materials, yet their mechanical strengths have been significantly increased. This work explores ductile aerogels in potential uses as constrained damping layers integrated into classical wallboards for drastically increased sound transmission losses without significantly increasing the board thickness and weight. Their ductility and mechanical strength enables light-weight X-aerogel panels of less than 1 cm in thickness to be integrated into gypsum wallboards. This work has experimentally investigated the integrated wallboards to achieve significantly increased sound transmission loss without significantly increasing thickness and weight of integrated wallboard system. This paper discusses preliminary investigations on experimental methods to characterize broadband dynamic properties of X-aerogels for better understanding of its excellent effect in drastically increased sound transmission loss. Some preliminary test results carried out in chamber-based random-incident measurements demonstrate high potentials in building acoustics applications and beyond.
Low thermal conductivity of classical aerogels has long been exploited, while their dynamic properties are yet to be further investigated. This work investigates a new class of acoustic materials based on porous hierarchical three-dimensional assemblies of organic nanoparticles. Primary polymer nanoparticles are formed via chemical reactions in solution and self-assemble to fractal porous secondary particles, which in turn become the fundamental building blocks of larger globular, fibrous or hybrid structures that form the microscopic network of highly porous monolithic materials referred to as polymer-crosslinked (or X-) aerogels. Their low-cost, thin-panel form has found potential applications as constrained damping layers integrated into gypsum wallboards. The standardized chamber-based random-incident tests demonstrate drastically increased sound transmission losses without significantly increasing the board thickness and weight when light-weight X-aerogel panels of less than 1 cm in thickness are integrated into gypsum wallboards in sandwich structure. For better understanding of its excellent effect as constrained damping layers, this paper discusses experimental investigations on broadband dynamic properties of X-aerogels with the intention to correlate their intriguing dynamic properties with increased sound insulations which will have high potentials as emerging building materials for advanced noise and vibration controls and beyond.
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