November 9, 2022 at 10:48 amjonlSubscriber
I need to check the contact pressure of an assembled shaft with hubs, but I'm struggling to get the initial setup correct. The hubs have different coefficients of thermal expansion.
The hubs will be heated to 200℃ and mounted on the shaft so that the hubs are in axial contact with each other. I want to check what the contact pressure is between the hubs as this assembly is cooled down. All the hubs have specified radial tolerances (at room temperature) so that they will fit the shaft when cooled. I need the model to have the right radial dimension of the hubs at room temperature (20℃) and at the same time have the hubs just touching axially at 200℃. How is this best achieved?
The material models have linear thermal expansion specified as secant CTE with a reference temperature of 20℃.
November 9, 2022 at 11:20 ampeteroznewmanSubscriber
Set the Environment temperature to 200 C because that is the temperature when the parts are assembled. Create the geometry so that each 200 C hub has radial clearance to the shaft at 20 C and that the two hubs are touching each other.
You will want frictional contact between the hubs and frictional contact be between each hub ID (Contact side) and the shaft (Target side)
You will need a gravity force to keep the two hubs touching each other as they shrink in length when the temperature goes from 200 C down to 20 C. At some temperature, one of the hubs will make contact with the shaft. At some lower temperature, the other hub will make contact with the shaft.
If Hub1 is the first to shrink onto the shaft, as Hub2 continues to shrink, I would expect a gap to open up between the hubs that were touching.
If Hub2 is the first to shrink onto the shaft, Hub1 will continue to touch Hub2 until it shrinks onto the shaft. But as both hubs continue to shrink, perhaps a gap is still created.
What the above scenario ignores is the temperature rise that occurs in the shaft as the hubs are cooling. That is where it gets interesting.
November 9, 2022 at 11:37 amjonlSubscriber
Thanks for the suggestion! The gravity load is a good idea for keeping the hubs in contact! What I've tried is to set the reference temperature of the hubs to 200deg and the thermal condition at t=0 to 200deg, and add the radial thermal expansion to the tolerance in the geometry. That way, all the parts have the right temperature at the start and the hubs don't expand into each other due to thermal strain. My only concern is whether I should change the reference temperature in Mechanical or the zero-thermal-strain reference temperature in Engineering Data. Are these essentially the same?
November 10, 2022 at 12:55 pmpeteroznewmanSubscriber
If the Hub ID geometry is constructed with radial clearance to the shaft when the hub is at 200 C, then 200 C should be the zero-thermal-strain reference temperature in Engineering Data. I think this is the same as setting the Environment temperture to 200 C in Mechanical.
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