3D-printed fiber-steered acoustic black hole beam for enhanced damping in low-frequency range

Acoustic black hole (ABH) beams are thin-walled tapered structures that mitigate resonance peaks above the cut-on frequency. An ABH beam with circular carbon-fiber paths in the wedge is proposed to overcome the trade-off between the low cut-on frequency and high specific stiffness of the host structure. The carbon fibers in the proposed structure were steered such that the axial Young’s modulus continuously decreased toward the taper tip. The viscoelastic properties of the carbon fiber-reinforced plastic (CFRP) and added damping layer were determined from tensile tests and dynamic mechanical analysis tests. The impedance matrix method was used to calculate and compare the reflection coefficients of three CFRP beams: circular fiber ABH, unidirectional fiber ABH, and uniform beams. The effects of design parameters of the circular fiber ABH wedge on the reflection coefficient were identified. Finite element analysis was performed to obtain the frequency response functions and modal loss factors of the three CFRP beams. The circular fiber ABH beam exhibited a lower cut-on frequency and higher modal loss factors than the unidirectional fiber ABH beam with the same dimensions. Steering carbon fibers not only reduced the cut-on frequency but also enhanced the wave-retardation effect and loss factor in the ABH wedge while maintaining a high host structure stiffness. The combination of a soft wedge for a low cut-on frequency and a stiff host structure also enabled damping enhancement for all resonance peaks. The excellent vibration-damping performance of the circular fiber ABH beam was validated via hammering tests on 3D-printed CFRP samples.