Short-term High Overload Under Rolling Bearing Destruction

The rolling bearings in the drive mechanisms of aerocraft usually run in a short running time and high-overload condition with a finite life span (less than several hours), clockwise and counterclockwise rotation, high reliability and no lubricant running. And the design must meet the small volume and light weight requirements of drive mechanisms. General bearings design and calculation are based on elastic theoretical formulas for long life span. In high cycle fatigue, the plastic contact deformation inside rolling bearings is much little than elastic deformation; but the plastic contact deformation under high-overload is signifecant, and this plastic deformation render bearings in jeopardy of being damaged. It needs special design if engineers choose existing commercialized rolling bearings, but there is no corresponding design theory. This paper aimed at needle roller bearings and angular contact ball bearings with short life span and high-overload and tried to analyze the overload capacity of bearings under this special condition and provide some theoretical groundwork for the design and application in practical engineering.Taking into account the elastic-plastic deformation, based on the semi-experienced formula of Palmgren, the load distribution and some affect factors such as clearance, manufacture precision, interference fit, etc, was analyzed. It was found by calculation that thrust load has an evident effect on contact angle while radial load influence feebly, clearance has a great impact on load distribution and appropriate interference fit increases carrying capacity, but the maximum needle burthen also increases. This paper also analyzed the maximum burthen of rollers or balls in overloaded rolling bearings and stuck load. Lubricant condition has a significant impact on bearings. The minimum oil film thickness and center oil film thickness in overloaded rolling bearings were analyzed based on the elastohydrodynamic lubrication theory. It was found by calculation that needle roller bearings have a adverse lubrication condition and it is very difficult to form a oil film, but angular contact ball bearings even have a reliable oil film when the total plastic deformation between inside and outside contact bodis amounts to one in a thousand ball diameter, if average roughness value of the contact surface is less than tenth micron. In compuer simulation, this paper analyzed the calculation precition of the finite element method to simulate point and line contact stress and deformation, and use ANSYS APDL language to build the hexahedral element model of a needle roller bearing and a ball bearing. Based on the analysis above, the brakage forms were proposed. This paper also tried to apply the calculation method above to stress verification of flexible ball bearings.