I've dealt with gears during my career, and need guidance to help with FEA assumptions. I need to figure out the worst case height of the contact area between two spur gears of equal face width. Material is 8620 steel, and the teeth are carburized to about 60 HRC. Would appreciate any guidance from you gear guys.

"FEA assumptions" correct term!! The worst case is the tooth tip. But, how realistic it is? How you translate "contact ratio", tooth deflection, tooth profile tolerances, involute deviations, etc. to FEA assumptions? This is why I do not think FEA is the approach for gear design. It may be helpful to determine root stress concentration factors, etc. This is why I would stick with the AGMA or DIN or ISO, etc. standards for gear design calculations which are based on semi empirical experience for many years.

"height of the contact area"
Not really sure what it is that you are asking.
Are you talking about spread center distance or tooth deflection?
A better description or diagrams would be helpful.

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia
http://www.aussieweb.com.au/email.aspx?id=1194181

fanman46,

Like the others, I'm not clear on what you mean by "worst case height of the contact area".

In the radial direction, there is a value used for bending/contact/scoring analysis called Highest Point of Single Tooth Contact (HPSTC), and any good gear text will provide the equations for calculating this value.

In the plane of contact, the values that define the hydrodynamic fluid film shape are the contact ellipse semi-width (height?) and semi-length. These values can vary greatly depending upon many factors, and calculating them with any precision is fairly complex.

If you wish to ignore the hydrodynamic effects and approach the problem as a simple 2D static hertzian contact (per unit length), then you will need to calculate the HPSTC/LPSTC values, the local tooth flank radius of curvature at which each occurs, and the surface normal forces being transmitted. Once again, this simplified approach would also ignore critical effects such as mounting errors, manufacturing errors, and structural deflections due to loads.

Here's a link to a technical reference: http://hdl.handle.net/2060/19920014293

Hope that helps.
Terry