Complex modulus driven low-frequency broadband sound absorption of acoustic functional composite material with transversely gradient-embedded SMA wires and optimization

This paper proposes a novel SMA rubber-based underwater acoustic functional composite material aimed at extending the lower frequency limit of sound absorption and enhancing broadband absorption bandwidth. Shape memory alloy (SMA) improves the pressure resistance of the anechoic coating. Additionally, its phase transition characteristics create a new energy dissipation channel for the rubber-based composite material by introducing additional strain and hysteretic loss through stress-induced phase transformation. Furthermore, the acoustic anechoic coating with transversely embedded SMA wires in a rubber layer containing conical cavities is developed. Using the Global Transfer Matrix Method (TMM) in combination with microstructural and gradient layering methods, the sound absorption coefficient curves of the coating at different frequencies are obtained. Through COMSOL finite element simulations and underwater acoustic tube experiments, the following findings are validated: (1) the correctness of the theoretical model, (2) the effectiveness of the novel structure in low-frequency sound absorption, with the lower frequency limit of the 0.7 absorption bandwidth significantly reduced from 730 Hz to 530 Hz, (3) the excellent pressure-enhancing effect of the transversely embedded SMA wires under static water pressure. Moreover, the influence of parameters including thickness, SMA volume fraction, and cavity radius on acoustic performance is analyzed. Based on this analysis, a multi-objective optimization is achieved using the Partial Least Squares (PLS) surrogate model and Differential Evolution (DE) algorithm, further lowering the lower frequency limit to 320 Hz. In conclusion, the novel composite anechoic coating demonstrates excellent global performance in broadband sound stealth characteristics.