A unified model for estimation of the friction coefficient of sliding isolators by means of small-scale tests

The coefficient of friction is a key parameter for the design of Curved Surface Sliders (CSS), as it defines the hysteretic behavior of the isolator and directly influences energy dissipation, displacement capacity, and recentering capability. While full-scale testing is required by current standards to characterize the effective coefficient of friction in both prototype and quality control tests, small-scale experiments are commonly used for the characterization of sliding materials for research and development due to their cost-effectiveness and feasibility. Today, the extrapolation of small-scale results to full-scale devices remains a critical challenge. To fill this gap, this study aims to propose a methodology to quantify the coefficient of friction of full-scale isolators by means of tests performed on small-scale specimens of the sliding material. Starting from established approaches developed to account for the dependencies of the coefficient of friction on mechanical parameters such as pressure, velocity and history of motion, a unified model is proposed, together with a practical procedure for calibration its parameter through small-scale tests. The proposed unified model is a semi-empirical formulation calibrated against measured data obtained from sliding tests. Its structure is informed by general physical considerations and by the experimentally observed dependence of friction on axial pressure, sliding velocity, and dissipated energy, while its parameters are calibrated against the test results. The accuracy of the unified model is eventually assessed by comparing its predictions with the experimental findings on full-scale isolators.