Surface Hardness-Case Depth Query 1

[morris9791]

Dear Experts,

I have 2 drawings (Pinion and Gear) which illustrates materials of class 86xx and 41xx with core yield of 500MPa and 850MPa respectively. Both have the same hardness specifications e.g.

30-45 HRc, case depth in mm with 50HRc and surface hardness up to 62HRc.

I need to do an ‘overload’ static bending strength calculations on both of these.

AGMA recommends taking the hardness at the core/core interface for static bending strength calculations. This Brinell value is obtained from their allowable stress versus Brinell Hardness table specified in the standard.

Is this a safe procedure, considering that the gear core may only be 500MPa as opposed to 850MPa despite the fact that both have the same hardness properties?

Thanks
Ed

 

[CoryPad]

When you say "same hardness properties", do you mean surface and case? Because the core hardness (which is routinely specified and measured for parts and used in calculations) for these two parts will not be the same. It is safe to use core properties for static bending strength because the case is thin (~ 1 mm) and though it helps, it doesn't contribute more strength than the core.