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Even though coned disk springs are widely used given their highly customizable design features, the literature on both analytical and experimental characterizations is sparse. This article overcomes the void by focusing on midrange displacements for a commercially available coned disk springs with square edges. A refined single disk spring model, capable of having asymmetric friction conditions imposed on the disk spring edges, is developed to predict the load-deflection and quasi-static hysteresis characteristics while relaxing prior limiting assumptions. A new quasi-static experiment is then proposed to measure the nonlinear load-deflection characteristics under four principal interfacial edge configurations — two symmetric and two asymmetric. In particular, the asymmetric friction conditions afford the opportunity to assess the validity of the long standing theory concerning the assumed location of the disk spring cross section rotation point. The imposition of asymmetric friction conditions on the disk spring also allows for the direct quantification of the contribution of asymmetric friction conditions on the disk spring contact edges. New analytical and experimental studies show that there are significant edge friction contributions to the hysteresis exhibited by the disk spring. Finally, stiffness parameters from both theory and experiment are briefly evaluated over midrange displacements. [ABSTRACT FROM AUTHOR]

A new dynamic experiment is proposed to estimate the coefficient of friction for a mechanical system with a combined rolling–sliding contact under a mixed lubrication regime. The experiment is designed and instrumented based on an analogous contact mechanics model, taking into consideration the constraints to ensure no impact and no sliding velocity reversal. The system consists of a cam (rotating with a constant speed) having a point contact with a follower that oscillates about a frictionless pivot, while maintaining contact with the cam with the help of a well-designed translational spring. The viscous damping elements for contact are identified for two different lubricants from an impulse test using the half-power bandwidth method. Dynamic responses (with the cam providing an input to the system) are measured in terms of the follower acceleration and the reaction forces at the follower pivot. A frequency domain based signal processing technique is proposed to estimate the coefficient of friction using the complex-valued Fourier amplitudes of the measured forces and acceleration. The coefficient of friction is estimated for the mechanical system with different surface roughnesses using two lubricants; these are also compared with similar values for both dry and lubricated cases as reported in the literature. An empirical relationship for the coefficient of friction is suggested based on a prior model under a mixed lubrication regime. Possible sources of errors in the estimation procedure are identified and quantified. [ABSTRACT FROM AUTHOR]

Abstract: A simplified translating friction element system is formulated, designed, and evaluated to simulate practical brake vibration (judder) issues. This simplified translating friction element system includes two frictional guides and two actuators to simulate dynamic interactions between the brake pad and the calipers (including the guide pins). First, a two degree of freedom nonlinear model and then a single degree of freedom linear model of the translating friction element problem are developed and solved for eight cases. Second, a simple laboratory experiment is designed, and the measurements are found to correlate well with the predictions of both mathematical models. Third, experiments and mathematical models are utilized to study the effects of the frictional guide and normal load application locations on a shift in the center of contact force. An effective torsional stiffness element is also defined to incorporate the center of contact force concept. Finally, a two degree of freedom nonlinear model of a simplified brake vibration (judder-like) problem is proposed, and the role of calipers on the dynamic response is discussed. [Copyright &y& Elsevier]

Abstract: A friction-induced forced vibration problem, as excited by the geometric distortions of the brake rotor, is studied in this article. The focus is on the order domain analysis, as the speed-dependent behavior of friction torque is not well understood. First, a new laboratory experiment is constructed to simulate vehicle brake judder in a scientific and yet controlled manner. The variations in pressure and torque are measured as the rotor slows down, and the order domain tracking is used to construct shaft torque vs. speed diagrams. A quasi-linear model of the laboratory experiment is then developed to obtain an analytical solution and to estimate the torque envelope function. A nonlinear model of the laboratory experiment (with a clearance) is also investigated to examine the resonant amplitude growth. Finally, predictions are successfully compared with measurements. Several contributions emerge over the prior literature. In particular, the experimental data clearly show that multiple-orders of the rotor surface distortion profile excite the friction-induced torque, and a clearance in the torsional system controls the resonant amplitude regime. New analytical and numerical solutions provide much insight into the speed-dependent resonant amplitude growth process. [Copyright &y& Elsevier]