Load on gear teeth

[DavidKhan]

My question may be very basic but let me ask it.

Mechanism Dynamic analysis calculates the forces acting on the gear teeth if it is a dynamic gear pair.That force acts at a point when we open the gear in creo simulate.we impart that load to the tooth surface to avoid stress concentration.Creo hadles the distribution but that distribution acts on the whole surface.Is there any other way to this to keep the load acting at the pith circle? Or to make a small surface at the pith circle portion and the apply the load to that insted of the whole tooth surface? and how to make the surface?

[JonathanHodgson]

You can create a Surface Region as a thin rectangle symmetrically about the line of contact.

However, unless you write some interesting equations you can only apply a constant pressure, instead of a Hertzian contact pressure distribution; and also the stresses you analyse in the gear will vary depending on the exact angle of rotation, since the contact line moves over the flank as the gears rotate.

If you do have accurate gear models, these days it's possible to run a contact model with both gears, but it's fairly slow to run and may not give useful answers unless you include misalignment between the gears, and tooth flank microgeometry; and even then you may need to run it at multiple angles of rotation to be sure you've captured the highest stress.

Usually when I load a gear, I'm looking at the stress in the rim under the tooth or in other areas of the component, not in the tooth root, and I just apply the load to the whole tooth surface.

If you want to calculate gear stresses, you're better to use a gear design program that calculates the stresses according to ISO 6336 or similar - such as Ricardo SABR/GEAR </plug>

http://www.ricardo.com/en-GB/What-we-do/Software/Products/SABR/Gear-design/

[DavidKhan]

Thanks Jonathan Hodgson

the gears i have are spur gears and are made according to thier equations.If i am not intrested in finding it contact stresses then applying the load at the thin rectangular region that i would create is good enogh? I mean if i consider the tooth as cantilever with load at the pitch circle and find the tooth bending stresses?

[JonathanHodgson]

Applying the load at the pitch circle is probably optimistic (will give lower than actual stresses), unless you have a very high contact ratio. The highest bending stress should be around the highest point of single tooth contact, which is probably outside the pitch circle.

Assuming you find the correct contact point then yes, you can get some good theoretical results - probably ignoring misalignment, as I mentioned.

If you have accurate gear geometry then I would apply the load as a pressure on a thin rectangle, and adjust the value of the pressure (use Review Total Load) to give the correct torque on the gear - this should give the correct load direction as well as magnitude.

Then you just need to know the material hardness gradient (assuming case hardened steel), the effect of shot peening and so on...

[DavidKhan]

Thanks Jonathan Hodgson .This will put me now on track.

[DavidKhan]

As only one teeth of gear is modeld through equation of involute ( Spur gear) and other are patterned or child of this teeth.

Now if i do creo simulate structral analysis i can suppress all the child or patterened teeth and apply load on the parrant to make it quick to solve.But the load is acting on any one of the child teeth and i apply it on the parrent teeth.althouthg all teeth are same and should be able to bear the same load.

Is suppresing child teeth is good?

Applying load on other teeth instead of the one near the pont automatically selected from Mechanism dynamics?

Why it gives error when i suppress all the child teeth?