Parameter identification of the fatigue-testing rig

In this paper the dynamic parameter identification of the novel fatigue-testing rig is presented. The applied identification method assumes a priori a simple dynamical model for which parameters are identified through free and forced vibration tests. The rig is comprised of two base excited oscillators providing the dynamic excitation for a fatigue sample and two pneumatic actuators preventing a loss of contact between the oscillators and the sample. The actuators introduce strong nonlinearities. All parameters of the system apart from the pneumatic actuators identified through the free vibration tests using the linear model were in a good agreement with those obtained by the frequency analysis. Two models, a linear and the nonlinear with Coulomb friction, were dynamically interrogated by a random excitation. It was shown that the stiffness coefficient a, increases linearly with the pressure in the pneumatic cylinders, and the viscous damping coefficient b increases quadratically with the air pressure in the pneumatic cylinders. The predicted responses for the linear and nonlinear models correlate well with the experimental data.