The way your are doing it is pretty common, but typically people use smaller angles- -6. Just be aware that if that were the stress you are concerned about, you are getting an approximation. Choosing a contact area is probelmatic unless you chose it from a good reference, like Roarke. Because, the contact area is in a sense the goal of your analysis. If you knew the contact area, you could compute the stress directly with a pencil. Also, the contact area depends on the material of the rail. The best way to model the contact between the rail and the wheel is to model the rail and fix it at the bottom. Then model the wheel and fix it so that it can move up and down only. Then apply 'no penetration' global contact and let it rip. This is going to take some horsepower, because 'no penetration' is a non- linearity which will terribly impact you computation time. Also, however you model it, run it over a few mesh sizes to verify the stress isn't going off to infinity.
You have to be carefull applying loads along split lines. In high speed, we measured the wheel load during a train running on a high. To calculate the contact patch size, we performed finite element analysis. Part I of this paper dealt with the physical nature of squat initiation on train. This however only occurs if the actual contact patch for a passing wheel matches.
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