High local stress at inside corner

[ptc-5182831]

We are trying to simulate a toothed-ring with radial loads outwards due to a shrink fit and rotation. In the corners of the valleys between the teeth, the stress is incredibly high compared to the stress in the rest of the part (see screen shot below with a thin red line at the inside corner).

Is this stress real? Should we simulate differently?

　

Thanks in advance for any advice.

　　

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[TomD.inPDX]

You have a stress riser in that corner. Try a generous radius. It is probably trying to "peel" the tooth away.

[dschenken · Accepted solution]

Yes and no.

If it is above the yield strength of the material the material will yield, lowering the stress in that area to the yield stress. Otherwise it is a significant stress concentrator/stress riser. If there is cyclic loading, this is where the part will fatigue and crack.

Anytime there is a rapid (dArea/dx or dSection Inertia/dx) change in section under a load the otherwise unsupported load has to go somewhere. Even a large-radius undercut will lower the stress.

Happily it also makes pop-top soda cans work.

[346gnu]

The stress is real in linear world but not in elastic-plastic world.

Elasto-plastic analysis will drop the stress, strain will increase. Stay below ultimate tensile strain.

Don't use vm stress.

Do the teeth drive anything?

[ptc-5182831]

Thank you for your response, that makes sense. Does Mechanica/Simulate do elasto-plastic analysis? We've never looked for it.

Thanks again!

[dschenken]

I guess you have to create a material with those properties at least.

http://help.ptc.com/creo_hc/creo30_pma_hc/usascii/index.html#page/pma/simulate/modstr/props/reference/elastoplastic.html

Not sure what needs to be done for the analysis, but maybe this helps

http://help.ptc.com/creo_hc/creo30_pma_hc/usascii/index.html#page/pma/simulate/analysis/struct/reference/plasticity_analysis.html

[ptc-5182831]

No, the teeth don't have any loads on them, so we don't need to worry about fatigue from cyclic loading. We have been experimenting with the elastic/plastic analysis and are getting results that are more rational once plastic deformation is modeled.

Thanks again!

Jeff

[ptc-5182831]

Thanks! We have already been experimenting with a radius, but other constraints mean that even a big one doesn't quite fix it, though it does help.

[346gnu]

Do the teeth drive anything?

Will they see variable tangential loading?

[sdensberger]

Jeff, is that the area of the highest stress? If so, to what % did the max_vm_stress measure converge to? What do your constraints and loads look like?

[ptc-5182831]

I will look at the convergence, that's a good idea. But yes, that is the area of highest stress, according to Simulate. Things are looking better using the elastic/plastic analysis.

Thanks again!

Jeff