Weld strength estimation on a drive shaft.
Weld strength estimation on a drive shaft.
(OP)
I am designing a drive shaft for an electric car that would be facing both bending and torsional stresses at the point of attachment of my sprocket. Various books are suggesting formulas and tables for weld thickness. Am confused as to which is the safest as am new to welding engineering. Your suggestions would be most appreciated.
A sketch of the problem is attached.
A sketch of the problem is attached.





RE: Weld strength estimation on a drive shaft.
RE: Weld strength estimation on a drive shaft.
RE: Weld strength estimation on a drive shaft.
One method would be to treat the welds as a line and workout the Section Modulus Zw for bending and Polar moment of inertia Jw for torsional load.
From this you can find the resultant force per inch on the weld then divide the answer by the allowable force per inch of the given weld size as laid down in standards, the result should be less than one.
I attach a method of calculating the weld stresses for a hitch which I did yesterday for another post on here.
The analysis is not appropriate for your case but it should give you the idea.
Have you considered fastening the sprocket be a different method ie- Shrink fit, keyway, I mention these as when you weld your sprocket on, the heat from the weld may cause distortion of the shaft and in addition you may need to stress relieve the weld to eliminate residual stresses that will be present after the welding process,especially if you have to do a fatigue analysis for this drive shaft.
RE: Weld strength estimation on a drive shaft.
Bribyk - How do you mean the shaft is likely to break? Is it from heat distortion. I can provide a heat sink.
desertfox - You have been most helpful. And yes, i did consider other ways. However, I was informed that a welded joint would be a viable and lasting joint if i could figure out how to accomplish it without destroying the shaft.
Thanks guys... I really appreciate this.
RE: Weld strength estimation on a drive shaft.
Bribyk - How do you mean the shaft is likely to break? Is it from heat distortion. I can provide a heat sink.
desertfox - You have been most helpful. And yes, i did consider other ways. However, I was informed that a welded joint would be a viable and lasting joint if i could figure out how to accomplish it without destroying the shaft.
Thanks guys... I really appreciate this.
RE: Weld strength estimation on a drive shaft.
What are the shaft and sprocket materials?
Ted
RE: Weld strength estimation on a drive shaft.
RE: Weld strength estimation on a drive shaft.
When Welding anything to anything I count on some resulting distortion. Problems I'd anticipate are Bent shafts, wobbling AND eccentric sprockets.
The nitrided surface may need to be ground away to produce a good clean weld.
"To weld a tuftrided or nitrided crankshaft, the journal or thrust needs to be underground first to remove this surface hardening. Then the weld can be applied." http://ww
RE: Weld strength estimation on a drive shaft.
Can you minimize the bending by providing more supports? Also, have you considered to provide shear keys to assist in resisting stress induced by torsion? I have no clue on behaviors of mechanical setups, just curious.
RE: Weld strength estimation on a drive shaft.
Thanks.
RE: Weld strength estimation on a drive shaft.
For not much change in shaft diameter you can significantly change the shaft capacity.
Be careful adding a keyway, that also adds a stress concentration factor to the shaft.
You could do both: increase the shaft diameter and use a keyway.
Ted
RE: Weld strength estimation on a drive shaft.
FS varies directly as the cube of the diameter, not inversely.
Sorry,
Ted
RE: Weld strength estimation on a drive shaft.
RE: Weld strength estimation on a drive shaft.
RE: Weld strength estimation on a drive shaft.
I was just having a look at your sprocket and shaft you posted at the start of the thread.
If you need to do a fatigue analysis on this shaft I should point out the the combined or principle stress on the shaft due to the bending and torsion loads is in the order of 176-177N/mm^2 which may be on the high side for your mild steel shaft when considering fatigue loading,so whichever method you choose to fasten your sprocket to the shaft it looks to me as though you might have to increase the shaft diameter.
regards
desertfox
RE: Weld strength estimation on a drive shaft.
RE: Weld strength estimation on a drive shaft.
your welcome
desertfox
RE: Weld strength estimation on a drive shaft.