The current study presents a multi-body dynamic model for investigating the vibration responses of a cylindrical roller bearing with localized surface defects such as dents on raceways. This model is developed with the assumptions that outer raceway is fixed in space and other elements have three degrees of freedom (DOF): two translations and one rotation. Centrifugal forces, gravity forces and slipping of the rollers are taken into account. The couplings of the Hertzian line contact deformation theory and the slice method are used to calculate all the contact forces. Local deflections due to defects are introduced into the constructed model by the time-varying deflection excitation. The equations of motion are established by the Newton-Euler method and solved by the fourth-order Runge-Kutta integration method with variable steps. Both time and frequency domains are used to analyse dynamic responses of the defective bearing. Some new components of the characteristic defect frequency can be seen from the results. The effects of time-varying surface models, different defect types and defect sizes on dynamic responses of the defective bearing are studied. An experiment is carried out to validate the proposed model. Comparison of the frequency spectrum in simulation results with that in the experiment shows reasonable qualitative agreement.

This paper presents a simplified model of misaligned-installing matched bearings, which is always constituted by two angular contact bearings in machine tools. Aiming at the effect of parallel misalignment arising in practical installing between two matched bearings, the nonlinear restoring force is derived and a matched bearings-rotor system model is established with Timoshenko elements. The Continued-Poincare-Newton-Floquet method is employed to analyze the global nonlinear characteristics with a varying clearance. Compared with the normally installed matched bearings-rotor system, it can be found that the amount of misalignment plays an important factor both on the global stability and vibration amplitude for a misaligned matched bearings-rotor system. The broadest unstable speed region always arise while the amount of misalignment equals to the initial clearance, and a slightly larger misalignment than the initial clearance can easily help the system from unstable dynamic behavior to periodic behavior. Meanwhile, a horizontal increasing misalignment will mainly affect the horizontal dynamic response by the way of magnifying and right shifting the vibration amplitude peak on speed axis obviously, but do a slight opposite effect on vertical normally installed direction. The results show that a proper amount of misalignment may be beneficial for the dynamic characteristic for the matched bearings-rotor system.

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