This presentation was made at the 2019 NAFEMS World Congress in Quebec Canada
Agnico Eagle is a mining company operating a gold mine in Val D'or, North Quebec. They are using an innovative rail hauling system consisting of a train of 64 cars on a monorail moving up ore from down the mine. The train is driven up by several stations along the rail where electrical engines are pushing the cars up via tires in contact with both sides of the cars.
Cracks started showing up on the frame of the cars after only several months of operation indicating fatigue problem. Finite Element Analysis (FEA) was used to assess the situation and solve the problem. The loading applied to the car when passing through a drive station was assumed to be the main problem. In drive stations, a tire rotating horizontally on each side of the car applies a normal force and a shear force to propel the car forward.
In order to realize a fatigue assessment using simulation, loads amplitude and variation on the cars must be known, but these loads are quite dynamic and varying as the train goes up full of ore, or goes down empty. Indeed, as the train circulates, there is a constant push and pull between cars, added to the side loads coming from the drive stations that are not accurately known and varying along the car length due to a displacement driven load.
The first step of the project was to realize a fatigue analysis using ABAQUS and Fe-Safe using a set of approximated static loads. While the analysis was successful in identifying areas of crack appearances, it was decided to calculate more accurately the loads using the True-Load technology. The same FEA Model of the car was used and loads coming onto the car were decomposed into a set of individual unit load cases and linear analyses were run to obtain the strain results on the model. Then True-Load was used to calculate the optimal location of a set of strain gauges that were installed on the car. Experimental tests were done at the mine to record strain histories when the train goes through a drive station while going up and going down.
Using the experimental strain histories, True-Load software was used to calculate loading functions in the FEA model that replicates the real strain histories. With these loading functions, FEA calculations were done showing the dynamic behaviour of the car in operation when passing through a drive station.
All load functions showed significantly more variation along the car’s length than expected and predicted by the preliminary FEA analysis. As the car goes through a drive station, loads from the tire and loads at the handles vary significantly showing push and pull behaviour. It was observed that the large difference in lateral stiffness of the car structure from the front to the rear of the car is in part responsible for the load variation. Indeed, with a displacement-controlled system for the drive station, changes in stiffness will result in changes in loads. Design modification of the car structure was recommended.
In such a dynamic application, accurate loads assessment is almost impossible unless measuring them during operations. Furthermore, when fatigue is studied, understanding of loads variations is very important as it can have a large impact on results. True-Load technology combined with ABAQUS was a big help to understand the dynamic loads on the car, which is an important step in order to improve the design and solve the problem.
|Date||18th June 2019|
|Organisation||Optimec Consultants Inc|