Study On The Alleviating Fretting Damages Of Spline Axle Through Tribological And Surface Engineering Design

Spline connection has the advantages of uniform force,small stress concentration,large contact area,good neutrality and steering,etc.,which is widely used in important connection occasions with high centring accuracy,large load or frequent slip.Due to the lack of lubrication,misalignments,variable amplitude torques and vibration condition,the fretting damage becomes one of the main failure forms of spline joint structure.Different from the traditional wheelset,the wheels and axles of China’s new generation of 400 km/h gauge-changeable high-speed trains are connected by splines,which can not only adapt to different gauges,but also achieve high-speed wide-area transnational transportation.As the key components,the reliability of the spline axles is related to the service safety of the whole vehicle.However,due to the complexity of manufacturing and variable application conditions,there is a lack of in-depth research on the fretting damage mechanism,and the surface engineering design and evaluation method of spline axles.This paper combines the finite element method,the surface engineering design,the tribological design,experimental research and the damage analysis method,selects the typical surface modification technology,and investigates the dynamic response and damage behavior of fretting wear and impact wear of surface modified layers.Then,on the basis of the above research,the paper discusses failure mechanism of the surface modified layers,and puts forward the optimization method of axle.Finally,the surface engineering design is verified by bench test.This paper has important scientific value and engineering significance.The evaluation system of surface engineering design and tribological design of spline axle to against fretting damage is established,which not only deepens the understanding of fretting damage mechanism of spline axle,but also provides theoretical guidance for the design of spline axle.The main conclusions are as follows:1.Contact mechanics analysis and optimum design of gauge-changeable spline wheel/axle structureBased on the three-dimensional model of the gauge-changeable wheelset,a fine finite element model of the spline wheel/axle is established,and the distribution of contact stress and slip under different working conditions is calculated.Under standard gauge,the contact stress of tooth surface is about 500 MPa when turning left,which rises slightly when turning right,and the relative slip of tooth surface is 5～15 μ m.The contact stress of the small cylindrical fit is about 50 MPa,and the relative slip is 75 μ m.The contact stress of the wheel-axle interface is in the elastic-plastic range,the slip between the contact interface is in the range of several microns to tens of microns,and the relative movement of the interface conforms to the characteristics of fretting.The contact stress of the spline tooth surface is much larger than that of the cylindrical fits,and the contact stress distribution of the tooth surface is strongly correlates with the working condition,and the misalignment condition is the worst.For spline axles of gauge-changeable trains,the structure optimization design should make the journal clearance in use state be 0.0 mm,the clearance of cylindrical fits is close to 0.0 mm,appropriate spline clearance,small pressure angle and long contact length.2.The tangential fretting wear behavior of surface modified layers under the different fretting running regimesThree kinds of surface modification treatments,i.e.,plasma nitriding,laser quenching,and laser cladding,are applied on DZ2 steel.The tangential fretting wear tests are carried out on the cylinder/cylinder contact to study the fretting wear behavior of the modified layer.Compared with untreated tribo-pairs,the surface modified layers significantly shift fretting regimes toward the lower displacement,and the mixed fretting regime decreased.In PSR,the fretting damage is marginal,and only micro-slip is observed.In MFR,the main damage mechanism of the modified layer is delamination accompanied by micro-cracks for LQ as well as oxidation.LC samples with a lowest hardness and its counter-body all show much lower fretting wear volume than PN and LQ samples with high hardness and its counter-body.In SR,the serious delamination and oxidation as well as ploughing are the main wear mechanisms.LC samples still have much lower fretting wear volume than both PN and LQ samples which have comparable fretting wear volume,but the counter-body of LC sample yet has more serious damage than that of both PN and LQ samples.3.The dynamic response characteristics and damage mechanism of impact wear for modified layers of spline axleThe dynamic response characteristics of the plasma nitrided layer and its substrate(axle steel)are investigated.Under the same impact wear parameters,the nitrided specimens show a lower energy absorption ratio and better impact resistance than the untreated specimens.The evolution of energy absorption ratio and cross-sectional profiles of wear zone reveals different damage forms.Plastic deformation occurs in the initial test of the untreated specimens,but elastic deformation is predominant for the plasma-nitrided layer.The main wear mechanisms of the untreated samples are pitting,delamination and oxidation wear.In contrast,the plasma-nitrided specimens exhibit better oxidation resistance and slighter peeling-off than the untreated specimens.The impact wear behavior of modified layers,i.e.plasma nitrided,laser quenching and laser cladding,are compared under the energy-controlled impact wear test condition,and delamination is the main damage form.In the initial stage of the test,the surface of the plasma nitrided layer is ground.With the increase of test cycles,the center of the contact zone forms a continuous smooth area after the delamination of surface material.For the laser quenching layer,material spalling and oxidation continue appears in the contact area.At the beginning of the test,the wear depth and width of the laser cladding layer increase significantly due to plastic deformation,but with the increase of test cycles,the spalling of the laser cladding layer is slighter than that of the laser quenching layer.4.Rotation bending fretting damage behavior of small-scale spline wheel/axleThe new type of high-speed small-scale wheel/axle rotating bending test bench can simulate the actual service conditions of spline axles with fretting damage.Small-scale wheel/axle structure has the same design as the original size of the workpiece,pair of materials,tolerance and surface treatment.Small-scale axles can load multiaxial cyclic loading of bending stress and the torsion stress.The rotating bending test results show that the interface of the spline axle with fretting damage happened,and the surface is covered with brownish red debris.The main damage area of the wheel seat can be divided into five bands(A～E),and the fretting damage tends to be worse follow the order of large cylindrical fit,small cylindrical fit and spline tooth.The fretting damage of untreated spline tooth surface is severe,and plastic deformation is observed at the contact edge.The propagation of microcracks extending into the subsurface layer are observed in the profile.Plasma nitriding can alleviate the fretting damage of the spline axle,and inhibit the initiation of cracks.Adding grease can further reduce the fretting damage of the spline axle.