Study on the Growth of the Fatigue Crack under Flexural Moment

Vehicles will suffer various loads in the moving process, and under the functions of various factors such as the ovality of the wheel, and the impacts to the rails when the vehicle passes the curve rail, the rail slot and the turnoff, the wheels will inevitably add normal loads to the rails, and the flexural moment will influence the generating and growth of the fatigue crack. To study the influences of flexural moment on the fatigue performances of rails with various materials, the experiments about the growth performances of the fatigue cracks of two kinds of materials including U71Mn and PD3 under the flexural moment are made on the NENE-2 fretting test machine, and according to the experiment results, the measures to reduce the fatigue of rails are proposed. The research analysis and experiment results indicate that the fatigue crack generates from the focal point of stress at first, and the main shearing stress is very important, and when the static load functions, the direction of crack growth will change by a large angle, but when the dynamic load functions, the direction of crack growth will be stable, and under same loading speed, the fatigue crack of PD3 rail more easily generates and grows than U71Mn rail. To prevent and reduce the fatigue of rails, the selection of rail should accord with the type of the route and the actual working environment of the rail, and in the heavy freight route, the PD3 rail with high mechanical strength should be selected, and in the high-speed route, the U71Mn rail should be selected.