Dynamic behavior and design optimization of a non-preload variable friction inerter: From experimental characterization to seismic performance

Traditional preloaded friction dampers rely on preload force to generate Coulomb friction. Increasing the preload force enhances energy dissipation but may also amplify the force transmitted to the primary structure, while preload relaxation can reduce the stability of the friction output during long-term operation. To address these limitations, a non-preload variable friction inerter (NVFI) is developed by coupling a displacement-driven normal-force mechanism with a ball-screw-based inerter. However, its dynamic behavior and multi-parameter interaction mechanisms under high-frequency excitations require further systematic investigation to ensure engineering reliability. This study conducts comprehensive dynamic and parametric tests on the NVFI. Based on the experimental findings, a high-fidelity constitutive model incorporating rate-dependent corrections is established. Subsequently, a Physical-Geometry Driven Optimization (PGDO) framework is proposed for the NVFI-structure system. This methodology translates experimentally quantified material wear thresholds and stiffness matching criteria into explicit mathematical constraints within a stochastic dynamic analysis. The experimental results elucidate the physical mechanisms governing the hysteresis evolution from a “butterfly shape” to a “bowtie shape” and identify the tribological stability boundaries of the phenolic resin-iron wire (PRIW). Furthermore, numerical analyses demonstrate that the PGDO-optimized system harnesses the inertial phase counteraction mechanism to effectively reduce the peak output force of the damper, while maintaining superior displacement control efficiency. This reduction decreases the force demand transmitted to the connection joints, thereby establishing a comprehensive, performance-oriented design paradigm transitioning from component-level physical characterization to system-level structural resilience enhancement.