Gear surface pressure
Gear surface pressure
(OP)
Where would you expect to get the max. pressure in a gear tooth? I have read somewhere that that is not on the surface, but slightly below.
Appreciate any input on this.
Appreciate any input on this.





RE: Gear surface pressure
Not sure of which stress component is displayed there
RE: Gear surface pressure
For stress, probably in the fillet root of the tooth.
RE: Gear surface pressure
Tmoose. Your picture (from a book cover?)shows max pressure or whatever is shown, slightly below the surface.
RE: Gear surface pressure
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There are factors which dictate the answer to your question, e.g. The coefficient of friction of the surface plays a large role if the max contact pressure will be on or below the surface. etc.
Hope this helps.
RE: Gear surface pressure
You need to clarify what you mean by "max pressure" in your gear tooth contact.
If your gear tooth mesh contact is oil lubricated and hydrodynamic in nature, then the max pressures will be a direct function of the maximum instantaneous EHL oil film pressures. And these dynamic oil film pressures vary over time depending upon the contact ratio, relative contact sliding/rolling velocities, pressure angles, radius of curvature, etc.
However, in regards to your OP and as others have noted, with surface compressive fatigue (like a gear contact) the typical failure mode is a sub-surface shear stress failure that results in a fracture which propagates outward to the surface and creates a spall.
References such as Roark's give a good approximation of the depth and magnitude of sub-surface shear stresses with elastic bodies in bearing under static conditions.
Good luck.
Terry
RE: Gear surface pressure
tbuelna: Yes, I am intersting in the sub-surface shear stress. And I think that when we talk FE analysis, the max sub surface stress is obtained by face pressure and not elemental shear stresses. I'll do a closer check in Roark's.