Comparative Performance Analysis of Inverse Phase Active Vibration Cancellation Using Macro Fiber Composite (MFC) and Vibration Absorption of Silicone Gel for Vibration Reduction

This study focuses on addressing the issue of unwanted vibrations commonly encountered in various fields by designing an Active Vibration Cancellation (AVC) structure using a flexible piezoelectric composite material macro fiber composite (MFC). A comparative performance analysis was conducted between the AVC and a traditional passive gel that continuously absorbs vibrations. The results showed that AVC was more effective in mitigating vibrations, making it a promising solution for vibration control. The results of this study from extensive vibration-sensing experiments and comparisons revealed that AVC effectively cancels the vibrations and vibration absorption performance of the passive gel. These findings underline the potential of AVC as an efficient method for eliminating and managing undesired vibrations in practical applications. Specifically, AVC demonstrated a high vibration cancellation ratio of approximately 0.96 at frequencies above 10 Hz. In contrast, passive gel exhibited a relatively consistent vibration absorption ratio, approximately 0.70 to 0.75 at all tested frequencies. These quantitative findings emphasize the superior performance of AVC in reducing vibrations to levels below a certain threshold, demonstrating its efficacy for vibration control in real-world scenarios.

Tunable network sound absorber based on additive manufacturing

Broadband sound absorption at low frequencies is always a challenge owing to the strong penetrability of acoustic waves. Combining detuned components, such as coupling curled Fabry-Pérot channels, has been proposed for broadband sound absorption. However, the components of the structure are generally arranged in parallel, so that it is difficult to assemble channels with gradient lengths into a compact and thin absorber. Tube networks, which can be seen as broadband and low-frequency sound absorbers, can circumvent this problem. However, the network absorber can only work at fixed frequencies once fabricated. Here, we propose a tunable low-frequency sound absorber consisting of honeycomb plates and detached chips and fabricate it by additive manufacturing. By replacing chips of the sound absorber, we experimentally validate different sound absorption spectrums. A low reduced frequency model and genetic algorithm are developed to design the chips according to targeted absorption spectrums. Moreover, we theoretically study the impact of radius of tube on sound absorption and extend the two-dimensional network to a three-dimensional structure. The remarkable efficiency and versatility of the tunable network sound absorber may pave the way for programmed absorbing material design.

Hierarchical pore structure based on cellulose nanofiber/melamine composite foam with enhanced sound absorption performance

For the preparation of high-performance sound absorption materials, the fabrication of hierarchical pore structure has proven to be an effective way. Herein, cellulose nanofiber (CNF) and melamine foam (MF) were combined by an environmentally friendly method for the first time, which endowed the final composite foam with both macropores and mesopores. The hierarchical pore structure was constructed by cyclic freezing-thawing, which enhanced the multiple reflections and micro-vibration of the sound waves, resulting in an obvious improvement in sound absorption performance. Specifically, compared with the unmodified MF, the sound absorption performance of composite foam with a thickness of 20 mm at 0.4 wt% CNF concentration showed an enhancement of about 107 % at 500 Hz and the NRC (noise reduction coefficient) had an improvement of 80 %. This work is expected to provide more inspiration for the design and preparation of high-performance sound absorption materials.

Electrically and thermally conductive underwater acoustically absorptive graphene/rubber nanocomposites for multifunctional applications

Graphene is ideal filler in nanocomposites due to its unique mechanical, electrical and thermal properties. However, it is challenging to uniformly distribute the large fraction of graphene fillers into a polymer matrix because graphene is not easily functionalized. We report a novel method to introduce a large fraction of graphene into a styrene-butadiene rubber (SBR) matrix. The obtained graphene/rubber nanocomposites were mechanically enhanced, acoustically absorptive under water, and electrically and thermally conductive. The Young's modulus of the nanocomposites was enhanced by over 30 times over that for rubber. The electrical conductivity of nanocomposites was ≤219 S m^-1 with 15% volume fraction of graphene content, and exhibited remarkable electromagnetic shielding efficiency of 45 dB at 8-12 GHz. The thermal conductivity of the nanocomposites was ≤2.922 W m^-1 k^-1, which was superior to the values of thermally conductive silicone rubber thermal interface materials. Moreover, the nanocomposites exhibited excellent underwater sound absorption (average absorption coefficient >0.8 at 6-30 kHz). Notably, the absorption performance of graphene/SBR nanocomposites increased with increasing water pressure. These multifunctional graphene/SBR nanocomposites have promising applications in electronics, thermal management and marine engineering.

The Synergy of Double Cross-linking Agents on the Properties of Styrene Butadiene Rubber Foams

Sulfur (S) cross-linking styrene butadiene rubber (SBR) foams show high shrinkage due to the cure reversion, leading to reduced yield and increased processing cost. In this paper, double cross-linking system by S and dicumyl peroxide (DCP) was used to decrease the shrinkage of SBR foams. Most importantly, the synergy of double cross-linking agents was reported for the first time to our knowledge. The cell size and its distribution of SBR foams were investigated by FESEM images, which show the effect of DCP content on the cell structure of the SBR foams. The relationships between shrinkage and crystalline of SBR foams were analyzed by the synergy of double cross-linking agents, which were demonstrated by FTIR, Raman spectra, XRD, DSC and TGA. When the DCP content was 0.6 phr, the SBR foams exhibit excellent physical and mechanical properties such as low density (0.223 g/cm³), reduced shrinkage (2.25%) and compression set (10.96%), as well as elevated elongation at break (1.78 × 10³%) and tear strength (54.63 N/mm). The results show that these properties are related to the double cross-linking system of SBR foams. Moreover, the double cross-linking SBR foams present high electromagnetic interference (EMI) shielding properties compared with the S cross-linking SBR foams.