Research On Delamination Damage And Failure Behaviors Of Thin Solid Lubricating Films Used In Rolling Bearings

Thin solid films can significantly improve the lubrication state at friction surfaces and/or interfaces,and thus they have broad application prospects in high-end bearings.In particular,thin hard solid lubricating films have excellent antifriction and antiwear properties,which provides an important technical means of improving the performance of rolling bearings under severe working conditions.However,due to the limitations of surface processing and film preparation technologies,the film-substrate systems consisting of thin hard films and elastoplastic substrates are prone to damages and failures,such as film cracking,interfacial delamination,and substrate plastic deformation,that seriously hinder their applications in engineering practice.Taking the thin solid lubricating films used in rolling bearings under low-speed and heavy-load conditions as the research object,this dissertation aims to study the damage and failure behaviors of film-substrate systems and focus on the interface delamination to provide theoretical guidance for the tribological design of solid lubricating films and their engineering applications in rolling bearings.Firstly,the quasi-dynamics method is used to analyze the contact characteristics of rolling bearings under typical working conditions,and the influences of rough topography on the external load characteristics of film-substrate systems under the point contact condition are studied with the semi-analytical method.Using nano-indentation,micro-scratch and other testing methods combined with finite element method(FEM)and extended finite element method(XFEM)and other numerical analysis methods,the bearing and damage-failure behaviors of thin hard diamond-like carbon films on the elastic-plastic steel substrates under local high contact stress are researched.Effects of the plastic deformation in substrates on the fracture damage and failure behaviors of the film are considered,and intrinsic material properties of the film system,including film fracture strength,toughness,interfacial adhesive strength,and critical energy release rate,are analyzed and characterized.Then,an analysis model of elastic hard films on elastic-plastic steel substrates indented by a spherical indenter is established.The bearing state and external loading evolution of the film-substrate system during the loading process are comprehensively analyzed to clarify the potential damages and failures,and the underlying mechanisms are revealed.On those bases,the cohesive zone model(CZM)and extended finite element method are used to simulate the interfacial delamination and film cracking,respectively.Their mutual influences and competitive failure behaviors are studied to analyze the ultimate bearing behavior and obtain the performance boundary of the system.Influences of interfacial adhesive parameters,film material properties,and geometric parameters on the damage and failure behavior of the system are researched.Subsequently,based on a deep groove ball bearing,typical thin hard DLC solid lubricating films are taken as the research object.Combining with the bearing quasi-dynamics analysis results,the equivalent contact finite element analysis model of the film-substrate system is built to analyze the bearing responses of the systems with different material properties and surface characteristics,which focuses on the effects of single rough peak contact.On those bases,a numerical analysis model was established to investigate the interfacial fatigue damage of the film-substrate system based on a cyclic cohesive zone model(CCZM).The influences of fatigue limit stress,surface frictional coefficient,load sequence,and rough contact morphology on the interfacial bearing and fatigue damage behaviors are studied.Therefore,a full-cycle rolling bearing solid lubricating film design and evaluation method is established,which covers early abnormal failure analysis and interface fatigue damage prediction.Finally,a multi-layer composite DLC solid lubricating film is prepared on the surface of bearing raceways,and the material parameters such as the film fracture strength,the interfacial adhesive strength,and the critical energy release rate are obtained by combining the experimental research with simulation analysis.The bearing performance and durability tests of the prepared solid lubrication bearing are carried out through the tests of starting friction torque,running friction torque,and working condition simulation life.Based on the test results,the bearing state and damage failure behavior of the film-substrate system in the main bearing area of the test bearing are analyzed.The influence and action law of rough surface morphology on the bearing and fatigue damages and failures of the film system under low-speed and heavy-load conditions are explored.