Determining the characteristics of viscous friction in the sliding supports using the method of pendulum

We analyzed the methods of determining the characteristics of friction based on the experimental studies using the damped oscillations of a pendulum. It was established that the available studies into characteristics of viscous friction lack the analytical description of the process of damped oscillations at viscous resistance and recommendations regarding practical calculation of the characteristics of friction. Here we propose a theoretical model of the swinging pendulum in the cylindrical sliding supports with a lubricant. It is demonstrated that for a pendulum in the lubricated sliding supports, the process of oscillations is described by a second order differential equation with viscous resistance, proportional to the deflection velocity of the pendulum. It is found based on the solution of the equation that the ratio of adjacent amplitudes of damped oscillations is a constant magnitude, hence it follows that the absorption coefficient is constant over the entire process. We established, based on the theoretical model of pendulum oscillations, that for the viscous friction the absorption coefficient is equal to the doubled logarithmic damping decrement and is determined by one or a cycle of oscillations. The formulas are received for calculating the indicator of dynamic viscosity of a lubricant in the contact by the decrement of pendulum oscillations damping. The developed procedures for determining the characteristics of viscous friction are applied to examine the contact- viscous properties of different combinations of lubricating and design materials. The results received are aimed at searching for design and technological solutions in order to reduce the energy losses to friction in the sliding supports of machines.