Stress concentration in a chamfer (rather than a fillet) of an axially

[patrickv]

Hello, I have a rod of two different diameters and I'm trying to find the stress concentration at the chamfer between the two diameters. I understand how to find the stress concentration factor, K, if the joint was a fillet (using r/d and D/d to find K in the appropriate table). However I can't find any way of getting K for a chamfered joint. Please help point me in some direction. Thanks so much. I've attached a quick diagram showing the filleted and chamfered versions of the shaft. The chamfered one is the actual piece I'm trying to find K for.

 

[desertfox]

Hi patrickv

I am unabe to find a stress concentration factor for your fillet.
I would use the radius value where the two diameters intersect which you can make extremely small and use this calculator:-

http://www.efunda.com/formulae/solid_mechanics/stress_concentration/calc_swss_p.cfm

Even at the intersection of the diameters you will not get a perfectly square shoulder, there will be a very small radius ie:- same radius as the tip of the cutting tool.

desertfox

 

[desertfox]

hi patrickv

I found this article:-

http://findarticles.com/p/articles/mi_qa3726/is_200209/ai_n9140709/

It states a shaft with square corners as 60% strength of the smallest diameter.

desertfox

 

[ColonelSanders83]

Have you looked in "Peterson's Stress concentration factors"? The book covers many different geometries, and most of the concetration facotrs you find are from this book.

Always remember, free advice is worth exactly what you pay for it!

 

[patrickv]

Thanks desertfox, I think I'll have to do that. Looks like the radius is only .015, but if that's the number I have to use, so be it. I thought for sure there would be tables for a taper like that.

Unfortunately colnel, I don't have access to the Petersen's book.

I appreciate the input though, if anything else pops up, let me know. Thanks.

 

[desertfox]

hi patrickv

your welcome

 

[rb1957]

there are Kt calculators on-line ... google, they should be there

 

[unclesyd]

How close would a round bar with a V-Groove come to OP's problem.

http://www.fatiguecalculator.com/probabilistic/index.htm

 

[rb1957]

not very ... it's probably not that different to a standard fillet, my guess is that the Kt is 10% maybe 20% higher (which i know can have a significant impact on life)

 

[ColonelSanders83]

If you are working with stress concentration factors you should consider the book a minor career investment.

http://www.amazon.com/Petersons-Str...=sr_1_1?ie=UTF8&s=books&qid=1262012846&sr=8-1

This way you will have the best information available without having to worry about it's correctness. If its for an important company project you boss may even pay for it.

Always remember, free advice is worth exactly what you pay for it!

 

[dineshmech]

Not sure if you have found a way to get K for a chamfered joint, but in general if you are working with strain gages in general, StrainMatics is a cheap working software that do most of the calibrations. Google it, you should be able to find it. I usually use it in conjunction with manufacturer's software or tables (futek in my case).

 

[flash3780]

Peterson's may have something for a tapered round beam (I don't have one in front of me, but it is "the place to look" for stress concentrations). Don't forget that there is, in fact, a radius at the root of the inside corner of your fillet. That's where your high stress is going to be.

Matter-o-fact, seeing as you have such a sharp taper, you may want to estimate the stress as a stepped shaft with a radius at the root (case 1 in your diagram). In that way, you can use the standard formula to estimate the stress concentration in the root of the fillet. Your answer should be a bit conservative, but pretty darn close.

If the radius at the root isn't currently defined, it should be. An uncontrolled inside radius is bad news. Strictly speaking, you could be building a crack into your design. So, step 1 would be to define it.

 

[unclesyd]

A full taper transition is better than a radius or taper radius transition. Her is a presentation that maybe of assistance with you problem. I don't have Power Point so it's jumbled when viewed in Adobe.

http://www.fatigue.org/minutes/Fall-2005/Microsoft PowerPoint - Curtis.pdf