#### SShep71

##### Hot Rolled

- Joined
- Sep 17, 2014

- Location
- San Diego, Ca

I have looked for an explanation, and asked for an explanation but all I get told/find is the projection method is industry standard because the actual method is too complex. THIS I have a problem with. Now, I know that in consideration of surface finish, bearing clearances and theoretical contact area being a simple tangent line of length L this is a simply complicated answer. I am approaching this from the perspective of contact area bearing surface under load after break in period (where the two surfaces have had time to wear together creating more than a theoretical contact). Wouldn't bearing stress being, Tau=(Shear force/area), be the shear force divided by the length multiplied by the contact area. The contact area being the length multiplied by half the circumference.

For example, a 20mm diameter shaft passing through a 15mm wide member according to what I can find the bearing surface area is calculated as 20mm x 15mm = 300mm^2. This is a 2 dimensional area calculation.

I argue that the calculation should, for the same setup, one half x (2 x π x radius of shaft) x length.

[1/2 x (2 x π x 10mm) x 15mm] = 471.238mm^2. This is a 3 dimensional calculation and more representative of the two surfaces in contact with one another under load.

I would expect that this is obviously more complicated than either method, as it would have to involve Integration to account for the round surface. I just cannot find the information, everything keeps going back to the "industry standard" method. Is the industry standard done that way because it is a "happy medium" between the extremes. I just find it obnoxious that something in engineering can be simplified to that but not explained better. Then again, considering the quality of some of the engineers I work with I can see why so many items are just garbage anymore.

I just don't want to be THAT kind of engineer, I learned all the trades and got all the experience first, now engineering school isn't turning out to be what I thought it was. Any insights here are greatly expected.

This Youtube video is the shortest and most to the point about bearing stress and it is the same reference I used for the calculation. All the other videos I have come across explain it the same way.