Three-dimensional finite element analysisof residual stresses in railway wheelsIntroductionManufacturing process such as casting or forging used in forming railway wheels induce a wide variety of residual stresses.Wheels are heat treated (Quenched or Annealed) which induces circumferential compressive residual stress in the upper rim thus increasing its surface hardness.Under service conditions, thermal brakes induces higher tensile residual stress which results in the formation of rim fatigue cracks.The stress analysis in railway rim wheel is done using three-dimensional elasticplastic finite element methodFig 1. shows finite element model used in residual stress analysis.Finite element modellingSimulation for residual stress is done in two parts:non-linear thermal analysis - determines the temperature distribution of the wheelnon-linear static structural analysis - distribution of stress over the wheel rimThermal analysis consist of four phaseshigh temperature step with water spray on the tread surface of rim (about 3 min) put in room temperature (about 6 min)elevated temperature draw (about 6 h) cooling in room temperature (about 7 h).

Results and conclusions

The heat treatment process cools the rim of the wheel much faster than the plate of the wheel. The rim-quenched wheels induces desirable residual compressive stresses in the upper rim, and improve the wear resistance which help prevent the formation of fatigue cracks at the tread surface of rim.According to Fig 2. the effects of water spray on the wheel rim cooling is visible. At the end of the quench, the minimum temperature in the wheel rim is 326 oC and the maximum is 802 oC , reduced little from the initial temperature of 869 oC.Fig 3. illustrates contour plots of the Von Mises stresses on wheel tread. For rail wheel, the magnitude of von Mises stress appears to be 553 MPa after heat-treatment. The magnitude of this stress is higher than the yield strength of the steel , which leads to plastic deformation. Thus, this analysis shows that the fatigue cracks initiate at a depth 45 mm below the tread surface for railway wheel.

Fig 3. Contour plots of the von Mises stress due to the heat treatment process of railway wheel analysis: (a) first phase, (b) second phase, (c) third phase and (d) forth phase.Fig 2. Contour plots of the temperature distribution (in C) due to the heat treatment process: (a) first phase, (b) second phase, (c) third phase, and (d) forth phase.Fig 1. Finite element modeling of wheel.

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