The Research On Fatigue Wear Mechanism Based On 35CrMo/GCr15 Friction Pair

Fatigue wear which exists in a variety of wear mode is a significant wear mechanism.There are the fatigue wear in the 35 Cr Mo/GCr15 friction pair both rolling and sliding,and this friction pair is formed by the beam supporting shaft of the pumping unit and the needle roller of the needle roller bearing without inner ring.Based on fatigue wear phenomenon in the friction pair,the fatigue wear mechanism is researched from three levels,which are sliding wear,plastic contact,asperity collision and asperity fatigue damage.The reciprocating sliding wear experiment,compression fatigue experiment and ring block wear experiment are designed and conducted to research the tribological characteristics of this friction pair in terms of delamination theory,contact theory and fractal theory.The contact mechanical behavior and fatigue damage of the asperity collision are simulated by finite element method(FEM).The main contents are listed as following:(1)The influence factors of wear volume are analyzed by the reciprocating sliding wear experiment.The sliding wear mechanism and fatigue mechanism of the 35 Cr Mo/GCr15 friction pair are researched.The load,reciprocating sliding frequency and their interaction influence the wear volume of the 35 CrMo specimen,their contribution are the load(50.70%),their interaction(30.42%)and the frequency(17.30%).The sliding wear mechanisms are different according to experimental condition.The delamination wear occurs when the load and frequency are boteh maximum,adhesion wear,oxidative wear and abrasive wear occur simultaneously.The fatigue mechanism in the sliding wear are strain fatigue and the delamination wear,and the main reason of the fatigue mechanism is crack induced by the plastic deformation in contact interface.(2)The relationship between the plastic contact area Arp,the plastic contact area ratio Arp/Ar on the 35 Cr Mo specimen surface and the wear mass as well as the fatigue mechanism are analyzed by the compression fatigue experiment and ring block wear experiment.It is consider that the change of the wear mass can be characterized by variable quantity of the plastic contact area ratio(?Arp/Ar),the wear mass increases with decrease amplitude of ?Arp/Ar.The material flaking in the plastic deformation caused by the strain fatigue and the delamination wear result in decease of plastic contact area.(3)The finite models of the 35 Cr Mo/GCr15 friction pair are established to simulate the asperity contact and collision in the sliding wear process.The asperity conllision's influence on the stress and strain distribution in the asperity are analyzed in different contact status of asperity,which are fully elastic contact,elastic-plastic contact ?,elastic-plastic contact ? and fully plastic contact.There is a loop of equivalent plastic strain peak in asperity in state of fully plastic contact status and the peak locates in the subsurface.The collision makes shear stress in the subsurface being fatigue load,and this fatigue load initiates the fatigue crack,the fatigue wear is resulted by the delamination which is formed by the fatigue crack extension.(4)The influence of cofficient of friction on Von Mises stress,the shear stress and the equivalent plastic strain are analyzed.The influence on Von Mises stress are different in different contact status,and the equivalent plastic strain increases with the cofficient of friction in the contact surface and the subsurface.The same result exists in the shear stress but the fully plastic contact status.(5)The asperity fatigue damage processes are simulated in different contact status.The fatigue damage initiates at the loop of equivalent plastic strain peak and in the loop interior when the asperity is in the non-plastic contact status.Alternatively,When the asperity is in the fully plastic contact status,the fatigue damage initiates firstly at the loop of equivalent plastic strain peak and then extends to the inner of the loop.The asperity fatigue failure initiates at the loop and extends to both inner and outer of the loop.In addition,more plastic deformation means more fatigue failure.(6)The shear stress ?xy is analyzed in the process of the asperities fatigue damage,the result shows that the shear stress ?xy has characteristic of fatigue stress.The amplitude of the shear stress changes in inner of the loop of equivalent plastic strain peak and both of amplitude and direction of the shear stress change in outer of the loop.