Press Fit Pressure
I think we all get in a bit over our head at times, you are not the only one, I still don’t know the half of it and I have been in engineering for more years than I can remember. The trick is knowing how to apply what you have been taught in college and I think this only comes with practice and experience and picking up pointers from other engineers.
Because initially we trying to calculate the circumferential stress; the area in question is the cross sectional area of the sleeve (or head). You are quite right – the press fit is applied to the same length of each piece – they cancel out. If it is any easier for you, let the length = 1inch. So the area is, the thickness of the piece x length of piece (or x 1). Once we have the circumferential stress, the radial stress can be obtained. Which is the stress we are really looking for.
Your second posting makes sense, the area this time is the circumferential area at the interface, because the radial pressure acts on the whole interface area. This area being Pi x interface diameter x length, only this time we must use the actual length to get the total force at the interface.
See also my earlier posting 10467.