Research On Mechanism Of Excitation And Dynamic Model Of Extended Defects In Rolling Bearings

Rolling element bearings are used in a wide variety of rotating machinery and their parts failure is one of the most common reasons for machine breakdowns.As the rolling elements pass through the extended defect,abrupt changes in the contact forces occur which change bearing stiffness,load distribution and vibration response of the bearing assembly.The contact forces and the bearing system properties are determined by shape and size of the extended defect.The understanding of the relationships between shape and size of the extended defect and the contact force,and as well as the bearing system characteristics,will directly affect the accuracy and reliability of the mechanical system fault diagnosis.Therefore,it is of great theory value and engineering significance to investigate the mechanisms and the dynamic models of rolling bearings with extended defects.The extended defects of rolling element bearings have been not yet accurately defined by now.This paper systematically classifies the bearing defects according to the size and distribution of defects,and lists the engineering examples.To overcome the problem that the contact relation between the rolling elements and the raceway cannot be accurately described by the model of rectangular defects,a new analysis model for describing the extended defects is proposed based on the shape characteristics of the extended defects.The entry-and exit-related vibration signatures are analyzed,and the influence of the extended defects on the beari ng vibration response characteristics is revealed.A finite element models of the self-aligning double row rolling element bearing with an outer raceway extended defect is modelled,which considers the contact stress and dynamic properties of the defective rolling element bearing.The stress distributions of all components of the initial state are analyzed.The model is numerically solved using the explicit dynamics finite element software package,ANSYS/LS-DYNA,to obtain vibration response of the defective bearing and dynamic contact forces between the rolling elements and the outer raceway.In-depth analyses of the dynamic interaction among elements of the bearings,and the relationship between the contact forces and the vibration response,are presented in this paper.Based on the contact relation between the rolling elements and the extended defect raceway,the formulations of load distribution and varying stiffness of the selfaligning double row rolling element bearings with outer raceway extended defects are presented.The effect of the size of the defect on the bearing system properties cannot be accurately described by prevously developed models of the bearings considering square-shaped defects.To overcome this problem,a multi-body dynamic model of the double row bearing with an outer raceway defect is proposed,which is based on Hertz contact theory.By analyzing the vibration response characteristics of the rolling element bearings with outer raceway extended defects,the problem that previous defect size estimate based on the time separation between the entry-and exit-related vibration signatures cannot distinguish between defects that differ in size by integer numbers of the ball angular spacing.By processing the experimental signals from the bearings with outer raceway extended defects,the numerical results from the proposed model in this paper are verified.