Stress anlysis and investigation of surface fatigue of PTFE-bronze layered journal bearings under dynamic loading conditions

SUMMARY Stress Analysis and Investigation of Surface Fatigue of PTFE - Bronze Layered Journal Bearings under Dynamic Loading Conditions In this study fatigue properties of plastic journal bearings including PTFE-bronze layer was experimentally investigated by using an experimental apparatus in which dynamic load is applicable in different forms, magnitudes and frequencies. The pressure distributions occurred at the surface of the journal bearing was determined. Further, stresses and deformations occurred at the journal bearing was calculated numerically by using ANSYS Finite Element Code. Experiments were carried out for the same loading at different bearing widths firstly and secondly for different dynamic loadings at constant bearing widths. Fatigue regions, capillary crack dispersion and stress distributions occurred at the journal bearing were investigated. The shaft orbit and fatigue regions occurred for each dynamic loading condition were determined. The relationship between fatigue region occurred at the surface of the bearing and pressure distributions were investigated by determining the circumferential pressure distribution under dynamic loading for the position of every 10° crank angle. Further, the relationship between fatigue regions and shaft center orbit and maximum value of dynamic load were investigated. Stress distributions at the surface of the journal bearing were determined by using Finite Element Method. The variation of the stress distributions at the interface of PTFE- bronze layer and the steel backing which is important in fatigue point of view were investigated. The equivalent stress distributions based on von Mises yield criterion were calculated and the critical points to initiate fatigue cracks in bearings were determined. At the end of this study, the maximum oil pressure and fatigue cracks were observed in the most heavily loaded regions of the bearing surface.. It was also found that the most critical region for stress distribution was found to be at the interface between PTFE-bronze and steel backing layers. Moreover, it was obtained that the axial stresses were effective as much as tangential stresses in fatigue failure of the journal bearings. It was calculated that PTFE-bronze layered journal bearings showed superior fatigue behavior than the bearings including white-metal alloy under the conditions tested in this study. Key Words: Dynamic Loaded Journal Bearing, Plastic Bearings, Pressure Distribution for Hydrodynamic Oil Film, Stress Distribution, Shaft Orbit, Fatigue. vni