Multi body dynamic (MBD) simulations and finite element analysis (FEA) used to live in separate worlds, but not anymore.
The simulation results on the left shows the residual stresses left in a rail after a passing wheel of a train wagon from a dynamic simulation.
In this simulation the vehicle dynamics were solved in Vi-Rail (from Vi-Grade) of a rail vehicle travelling over an irregular track (Video 1), causing the lateral movement of the wheel and varying vertical contact forces. The wheelset's lateral and longitudinal movement was then exported along with the vertical wheel forces and applied to a rigid wheel in Marc (Non-linear FEA solution from MSC Software). Due to the material in the contact patch, exceeding it's yield point, residual stresses remain after the wheel has passed.
In both the dynamic and FEA results the multi point contact between wheel and rail could be detected in certain locations, with it being clearly shown in the FEA results where the contact points shifts from one to the other as the wheel moves inward.
The following steps were required to complete the above process:
- Conduct dynamic analysis in Vi-Rail
- Identify section of interest in results (long section for FEA analysis may not be feasible)
- Export the wheel set's lateral and longitudinal displacement and vertical loads over distance/time
- Create a rigid (geometry) wheel from the wheel profile xy coordinates in the Vi-Rail wheel property file.
- Import xy points of wheel profile as ACIS file
- Create curves between points
- Revolve curves into surfaces about the rolling radius relative to the profile zero point
- Following the same procedure, create a 3D rail from the Rail profile, track and irregularity data from Vi-Rail files
- Create a feasible mesh for contact analysis of the Rail - Since Marc can auto refine the elements in contact, only the curvature need to be captured well.
- To capture residual stresses, material stress-strain data need to be provided.
- Constraints of the model need to be considered carefully
- Symmetry constraints on the rail ends are undesirable since it would duplicate the load effect near the ends and prevent rail rotation
- Supporting constraints need to reflect the same rail freedom a rail in track would have on pads, sleepers (ties), ballast and formation
- Sensitivity studies can be conducted to establish the amount of detail required to study the desired effects effectively