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Figure 2: Material data from experiments and data used in the FE analysis with ABAQUS.

4 NUMERICAL SIMULATION OF FLASH-BUTT WELDING OF RAILS Flash-butt welding is a resistance welding method. An electric potential is applied between two pieces of metal which are clamped adjacent to each other. This results in a current flow through the circuit which is sufficient to produce a flashing action. The metal is heated to the fusion point and the weld is completed by applying an upset force.

The welding operation comprises three steps: preheating, burning-off and upsetting. Preheating is performed by pressing the two rails together and separation of them as an electric current passes across the interface. In the second step, the edges are slightly parted and a low voltage is applied between the ends causing a flash arc. The surfaces are cleaned and uniformly heated during this step. In the third and last step, the upsetting, a force is applied rapidly, which forge the two ends together, and the molten metal between the ends are expelled.

The finite element simulation of the flash-butt welding process was carried out in a sequence, starting with an electro-thermal analysis that provides a temperature field history to the subsequent thermo-mechanical analysis; see Skyttebol et al. [5] for more details about the welding simulation. The option of geometrical nonlinearities in ABAQUS was used for the latter analysis, as well as for the train-track-rail interaction analysis with the rail model in Section 5.

5 NUMERICAL SIMULATION OF TRAIN-TRACK-RAIL INTERACTION An FE tool was developed in previous work for the analysis of rolling contact fatigue (RCF) of railway rails; see Ringsberg et al. [8] for details. It can mimic the wheel-rail rolling-sliding contact on a track, since it incorporates both the dynamic global track response and the three-dimensional local elasto-plastic contact conditions in the rail head. Two FE models, for track and rail, which are coupled by time-dependent boundary conditions, form the FE tool. An elastic FE analysis using the track model calculates time-dependent displacements at two cross-sections 12 cm apart; these are then used as boundary conditions in an elasto-plastic FE analysis using the rail model. As a result, the influences of both the dynamic global track response and the three-dimensional local elasto-plastic material response in the rail are incorporated in the rail fatigue or stress analysis.

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