Analysis And Research Of Fretting Damage On Wheel/RD₂ Axle Interface

As a common method to assemble mechanical parts, the interference-fitted joint is used for torque and axial force transmission. Although this structure is simple, there are many advantages:high centering precision, high joint strength, high carrying capacity, and high reliability in shock and vibration case. Wheel and axle joint is a typical interference-fitted joint in railway wheel set. Theoretically interference-fitted axle with the wheel is closely connected, but there is fretting damage and fatigue cracks on wheel seat actually, the fatigue cracks may lead to axle fracture, the driving safety will be influenced.In this paper, wheel set which is assembled by RD2 type axle and monobloc steel wheel is taken as a research object. The basic technique and parameters of wheel set assembling are introduced. Force analysis of axle is carried out. The bending stress of RD2 axle and calculated the strength of wheel seat are calculated. Combined with stress analysis and fretting theory, surface damage mechanism of wheel/axle interface is analyzed and researched.Firstly, this paper introduced the technics process of wheel/axle assembly, and compared the requirements of interference and pressure between domestic and abroad. The influence of surface damage on wheel set is disucussed in interference, pressure, figure, tolerance, surfaceness and assembly technics.Secondly, Force analysis of axle was carried out; bending stress of RD2 axle and the strength of wheel seat are calculated. The calculated results according to TB/T 2705-1996 and JIS E4501-1995 were compared. It shows that using the calculation method in JIS E4501-1995, the fatigue strength on wheel seat of the new axle can be satisfied with strength requirement, but the fatigue strength on wheel set of the repaired axle is not qualified.Finally, in order to avoid an additional degradation of surface caused by the classic method of wheel-axle disassembled with press, an in-situ cutoff of the wheel is performed, and the wheel/axle joint is separated to directly examine the damage behavior of the contact surface. Microscopic examinations in combination with mechanical analysis show that composite fretting is occurred and there are two circular worn zones of about 20mm in length at the edges of the interface, accompanying with some micro-cracks. The degradation feature corresponded to the mechanism of fretting wear and fatigue. Current palliative measures against fretting damage of the axle have been reviewed and some suggestions have been put forward.