Effect of multi-layered IIR/EP on noise reduction of aluminium extrusions for high-speed trains

Damping treatment is effective for noise and vibration control. However, there is a lack of research on the relationship between the fabrication and mechanical property characterisation of damping materials and the vibroacoustic characteristic analysis after damping materials are applied to actual composite structures. We performed such a study. First, modified butyl rubber (IIR) with high damping performance was prepared, and its frequency-dependent elastic modulus and loss factor were identified. Second, the vibration and damping characteristics of the modified IIR used in multi-layered constrained-layer damping (MLCLD) were investigated via cantilever-beam experiments and simulations. Third, the noise reduction (both sound radiation and sound insulation) effects of the MLCLD on aluminium extrusions were examined using prediction models, which were validated according to acoustic laboratory tests. The results indicated that the structural vibroacoustic characteristics are affected by not only the number of layers but also the application objects, structural parameters, and material properties. The final lightweight optimisation design of the aluminium extrusion using the MLCLD reduced the radiated sound power level by 2.7 dB, improved the sound insulation level by 3.0 dB, and reduced the total mass by 14.4%.