Experimental identification of high damping ratios in single-degree-of-freedom systems

A curve-fitting technique using a minimum error criterion was presented for identifying higher damping ratios near the critical damping ratio in single-degree-of-freedom systems. Free vibration decay tests were performed on a linear spring–mass–damper system with constant initial conditions using a modified commercial vibration apparatus. A vibration mass was supported with an extremely low-friction air-bearing guide. Mass displacement was measured using a laser displacement sensor. The magnitude of the viscous damping forces was varied and controlled using an electromagnetic damper installed in the apparatus. Higher damping ratios (\(\zeta\)> 0.8) were accurately identified using the curve-fitting technique, while lower and medium damping ratios \(\left( {0 < \zeta < 0.7} \right)\) were estimated using the conventional logarithmic decrement method from the measured free vibration decay curves.