Fatigue Pitting Failure Analysis of Tooth Surface of Spiral Bevel Gear for EMU Train

In order to overcome the fatigue pitting failure of tooth surface of spiral bevel gears for electric multiple unit (EMU) trains, the pitting failure locations were firstly summarized and both macro-and micro-morphologies of the pitting fracture surfaces were investigated. Then, based on the track test of EMU trains in practical service, the load spectrum of gear was compiled thoroughly, and the contact stress of gear was calculated according to the ISO 10300-2-2001. In addition, a series of bench loading tests under different operational conditions were conducted to obtain the variety law of the contact area. At the condition of the equivalent loading torque, the lengths of Herz contact lines and the diameters of pitch circles were determined in the contact area of cylindrical gear and that in the normal direction at the tooth width center, and the contact stress and contract area of gears were also analyzed. The results show that the concave contact area at the end of small gear teeth of the driven spiral bevel is the normal contact area under variable loading conditions, while the contact area would be off the tooth width center line under the equivalent torque loading condition. When the length of contact line and the diameter of pitch circle are less than those obtained from theoretical analysis, the actual contact stress (972.23 MPa) will be larger than the theoretical contact stress (777.26 MPa). As a result, in order to avoid the fatigue pitting failure, it is suggested adjusting the contact area of gear concave to the center of tooth width under the equivalent torque loading condition.