Three-dimensional finite element analysis of residual stresses
in railway wheels
Introduction:
Manufacturing process used in forming railway wheels induce a
wide variety of residual stresses. It is desirable to have less
residual stress and in the railway wheel manufacturing process, a
heat treatment such as forging or casting is done which induces
desirable circumferential compressive residual stress in the upper
rim. This decreases the risk of rim crack initiation (due to high
residual stress) by increasing the surface hardness.
But under service condition, the thermal brake loading on rim
wheel develops higher tensile residual hoop stress which
contributes to help the formation of rim fatigue cracks. They
indeed reduce fatigue strength and exacerbate the effect of cracks
and material defects.
The stress analysis in railway rim wheel is done using
three-dimensional elasticplastic finite element method. Finite
element models of this nature generally need a fine mesh to achieve
accurate results.
Finite element modelling:
In this simulation for residual stress two parts of analysis are
used; non-linear thermal analysis and non-linear static structural
analysis. The non-linear thermal analysis determines the
temperature distribution of the wheel that varies over time and the
distribution of stress over the wheel rim is done in non-linear
static structural analysis.
The heat thermal analysis consist of four phases; first is high
temperature step with water spray on the tread surface of rim
(about 3 min) then, put in room temperature (about 6 min), the
elevated temperature draw (about 6 h) and finally, time for cooling
in room temperature (about 7 h).
The heat treatment process cools the rim of the wheel much
faster than the plate of the wheel. The rim-quenched wheels
strengthen the steel, induce the desirable residual compressive
stresses in the upper rim, and improve the wear resistance.
The beneficial residual compressive stresses are known to help
prevent the formation of fatigue cracks at the tread surface of rim
and therefore they are significant to the trains safety.
The input parameters included material properties, temperatures,
times, and boundary conditions, which were thought to affect the
residual stress field. The parameters required for the analysis of
heat transfer, including thermal conductivity, and specific heat.
Thermal conductivity k, the ability of the material to conduct heat
energy is described by a transfer of property is usually expressed
in units of W/moC. This value varies with temperature as an input
to the application is given. Since the heat transfer analysis,
including free expansion, so the specific heat at constant pressure
of the material (Cp) is used.
Convection occurs throughout the process of quenching and
annealing and radiation is also permitted.
Result and Conclusion:
Three-dimensional finite element analysis for simulation of
residual stresses in railway wheels is developed in this paper,
which is based on the residual stresses from heat treatment
process. For this purpose, Non-linear 3-D finite element analysis
is used for residual stress.
The following conclusions can be made:
1. The resultant stress field is high value and their effects
are not negligible in the crack initiation.
2. The results revealed that stress field is highly sensitive to
the variable thermal loads which makes it a very significantly
factor affecting the stress field of railway wheels.
3. The railway wheels are rim-quenched using a water spray to
induce beneficial hoop residual compressive stress at the tread
surface.
4. Results of the baseline analysis suggest the presence of a 45
mm thick residual compressive layer with stresses as high as 553
MPa in the wheel. Therefore, the residual stresses have a
significant effect on fatigue life.
References:
[1] Reza Masoudi Nejad. Using three-dimensional finite element
analysis for simulation of residual stresses in railway wheels
[2] Farrahi GH, Tirehdast M, Masoumi Khalil Abad E, Parsa S,
Motakefpoor M. Failure analysis of a gas turbine compressor
[3] Farrahi GH, Majzoobi GH, Hosseinzadeh F, Harati SM.
Experimental evaluation of the effect of residual stress field on
crack growth behaviour
[4] Okagata Y, Kiriyama K, Kato T. Fatigue strength evaluation
of the Japanese railway wheel. Fatigue Fract Eng Mater Struct
2007;30:35671.
