Experimental investigation on a novel tunable quasi-zero-stiffness vibration isolator: soft-granular-piston

This paper introduces a novel tunable quasi-zero-stiffness (QZS) vibration isolator (QZS-VI), which effectively extends the bandwidth for low-frequency vibration mitigation. The proposed QZS-VI utilizes a soft-granular-piston (SGP) architecture, in which a threaded piston rod is integrated within an adjustable and tightly confined soft-granular chamber. This design enables the tuning of nonlinear mechanical properties through control of the volumetric compression ratio (VCR) of the confined soft-particles housing. The restoring force of the SGP-based VI is experimentally characterized and described using an exponential decay model. The underlying physical mechanism is further explored via the discrete element method (DEM) based on a modified Hertzian contact model. To evaluate the vibration isolation performance, transmissibility tests are conducted under varying VCR values and payload masses. Results demonstrate that by adjusting the VCR value, the transmissibility of the system can be significantly reduced under different payloads for broad-frequency excitation, particularly in the low-frequency region. The proposed SGP-based QZS-VI shows considerable promise as a tunable VI suitable for applications involving random low-frequency excitation.