Study On Torsional Fretting Wear Oriented To Blade Bearing Interface Of The Controllable Pitch Propeller

The controllable pitch propeller(CPP)is a key part of the oceanic dynamic positioning system.During service of the CPP,fretting wear and sliding wear happens respectively at the blade bearing interface when the pitch is fixed and adjusted,leading to the reduction of pitch adjustment flexibility and failure of dynamic seal.In this paper,wear mechanisms of the blade bearing were studied,the effects of assembly and operation parameters and preparation process on the wear performance of the blade bearing were discussed.This work provides a theoretical basis for optimizing the preparation process and assembly and operation parameters to improve the service performance and prolong the service life of the CPP.The main work and achievements of the dissertation are as follows:In view of the need to study the wear mechanism and influence rule of the blade bearing interface,a new torsional fretting wear test platform with flat on flat contact was developed according to the fretting wear condition of the blade bearing interface during service of the CPP.The platform makes up for the insufficiency of the traditional fretting wear experimental platform in the fretting mode and contact form for fretting wear study of the blade bearing interface,and can be used to study the fretting and sliding wear behaviors of the blade bearing with different preparation process and under different assembly and operation parameters of the CPP.In the light of fretting wear and sliding wear coexist on the blade bearing interface but it was unclear which of them was more serious,comparison and analysis on fretting wear and sliding wear were carried out with the flat on flat contact torsional fretting and sliding wear experimental platform.Experiments under different normal loads and lubrication conditions were carried out on the basis of the actual working conditions of the blade bearing interface.Based on the normal loads and lubrication conditions in real case,fretting and sliding wear experiments were carried out,the surface work hardening,surface topography,wear volume and third body solid lubrication effect were analyzed,and it was shown that fretting wear was the main reason leading to the wear failure of the blade bearing interface.To investigate the influence of the assembly and operation parameters on torsional fretting wear behaviors of the blade bearing interface,a series of torsional fretting wear experiments under different normal loads,angular displacement amplitudes and lubrication conditions were carried out.The influence of normal load and angular displacement amplitude on the fretting running states was revealed according to the fretting map theory.The relationship between the angular displacement amplitude and the surface damage mechanism was established by analyzing the accumulated dissipated energy and the wear volume data comparatively.Based on micro topography characterization of the worn surface,wear mechanisms of the blade bearing interface under different lubrication conditions were revealed.Specifically,they were mainly abrasive wear and plastic deformation under oil lubrication;theyweremainly abrasive wear,cracks and delamination under filtered water and artificial seawater lubrications,and corrosion in artificial seawater as well;they were mainly abrasive wear and oxidative wear under dry fretting.To optimize the surface morphology of the blade bearing surface,surface topographies at various process levels were prepared and a series of torsional fretting wear experiments were carried out to explore the effect of surface texture direction and surface roughness.Based on surface lubricant storage effect analysis,asperities contact stress analysis,wear depth analysis and worn surface micro-morphology analysis,the influence law and damage mechanism of surface roughness on the friction torque and wear volume under different lubrication conditions were revealed.Finally,according to the actual working conditions of the blade bearing interface,the conclusion was obtained that by preparing surface topography of the blade bearing interface with texture perpendicular to the relative movement direction and S_a range between 0.8μm and 1.2μm,the fretting wear performance can be the optimal.Based on abrasive wear,plastic deformation and adhesive wear analysis that existed on the blade bearing interface,an effective method to improve the fretting wear performance by preparing PVD TiCN wear-resistant coating was proposed.After preparing the PVD TiCN coating,experiments and analysis under different lubrication conditions were carried out,proving the effectiveness of the coating preparation for improving the wear resistance of the blade bearing interface.The wear mechanism,wear resistance enhancement mechanism and tribochemical behavior of the coating under different lubrication conditions were revealed and clarified with optical microscopy analysis,scanning electron microscopy analysis and X-ray photoelectron spectroscopy analysis.This work provides a theoretical basis for reducing the fretting wear of the blade bearing interface by preparing PVD TiCN coating on it.