ACOUSTIC BLACK HOLE EFFECTS IN THIN-WALLED STRUCTURES

Propagating flexural waves in structure can be manipulated through the so-called Acoustics Black Holes (ABH) effects. Upon a proper tailoring of the structural thickness, the phase velocity of the bending wave gradually reduces alongside thickness thinning, thus entailing high energy concentration and effective energy dissipation using a small amount of damping materials. The phenomenon arouses increasing interests from the scientific community and inspires innovative design solutions for lightweight and highly damped structures. The topic has been widely explored, mainly for thick-walled structures. Whether sensible ABH effects can still be produced in thin-walled structures through proper design remains unknown. In this paper, we report thorough numerical and experimental investigations to demonstrate that ABH effects can be readily achieved in a compound ABH structure of thin thickness with viscoelastic material filling. The compound structural design makes effective use of both ABH effects and the shear effects of the damping material, mainly along the mid-plane of the structure, to collectively generate a significant enhancement of the structural damping. While the shear-induced damping dominates the lower frequency region, ABH-induced damping becomes dominant once the ABH effect is cut-on. A good compromise between the two effects requires the stiffness of the damping materials and other ABH parameters to be properly chosen in order to ensure broadband benefit in terms of vibration reduction through damping enhancement.