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.
Improved simulations are created to mimic the nature of compressive failure related to macro-structure and loading direction in fuse deposition modeling (FDM) additively manufactured nylon parts. Unlike prior work, the simulations incorporate internal fluid cavities to model the effects of entrapped gas within the internal geometric voids. Until now, such modeling technique has only been applied in simulations involving polymer foams. Experimental tests are also conducted to provide a baseline comparisons. The nylon FDM specimens studied vary in terms of infill pattern (hexagonal, triangular, and rectilinear) and infill density. Compressive loads are applied in orthogonal part directions to examine degree of anisotropic compressive strength at onset of permanent deformation. A comparative simulation study with and without the fluid cavity modeling reveals how the accuracy of the results improves when the effects of the entrapped gas is included. The aim of the work is to help establish an improved general method for creating simulations of sufficient fidelity to predict part macro-strengths for various 3D printed infill patterns and densities without the need for time-consuming experimental analyses for every variation in geometry.
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