Gear surface pressure

[izax1]

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.

 

[Tmoose]

http://www.me.metu.edu.tr/courses/me307/useful/1c-300.pdf

Not sure of which stress component is displayed there

 

[dinjin]

Probably the highest point of single tooth contact.
For stress, probably in the fillet root of the tooth.

 

[izax1]

Thank sfor feedback. My question is about max.pressure, not max stress.

Tmoose. Your picture (from a book cover?)shows max pressure or whatever is shown, slightly below the surface.

 

[Timusop]

izax1, I would suggest you do a little background reading on Hertz contact theory, Timoshenko is a classic:

http://www.scribd.com/doc/6603146/Strength-of-Materials-Parts-IIITimoshenko

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.

 

[tbuelna]

izax1,

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

 

[izax1]

Thanks for responses

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.