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hub on shaft stress conctration factors
- Thread starter Tmoose
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Online resources for Interference Fits may be of some benefit to you here. Look for the lecture notes from University of Tennessee at Martin or perhaps Thick Wall Pressure Vessel Theory as applied to Lame's Equation(s).
I'm not sure if you want shrink fit studies or simply the bending moment induced by some hub loaded at the rim on the shaft. Such a case could be handled as an eccentric load in the transverse case.
I'm not sure if this helps. Good luck none-the-less.
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada
I'm not sure if you want shrink fit studies or simply the bending moment induced by some hub loaded at the rim on the shaft. Such a case could be handled as an eccentric load in the transverse case.
I'm not sure if this helps. Good luck none-the-less.
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada
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- #4
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- #6
bending load. The clearance is used up on one side.
ok now i'm confused, a fairly normal state of affairs.
the pictures clearly show some bike forks being bent by a normal load introduced by the front wheel (like they hit something). isn't this a simple bending problem ? and if you've got a fatigue load, this geometry is simply a shaft in bending, no?
the pictures clearly show some bike forks being bent by a normal load introduced by the front wheel (like they hit something). isn't this a simple bending problem ? and if you've got a fatigue load, this geometry is simply a shaft in bending, no?
GregLocock
Automotive
I don't think the tube would attain its full bending moment, before failure, because the state of 3 dimensional stress would not obey classic beam theory.
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Greg Locock
SIG
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Greg Locock
SIG
lease see FAQ731-376 for tips on how to make the best use of Eng-Tips.- Thread starter
- #9
No forks, sorry. Just intended to be an example of bending applied to a shaft, and in the case of the motorcycle fork, thru a clearance fit like mine.
This is actually a heavy hollow shaft gear reducer cantilevered on a smallish vertical shaft. Our stress group applied factors for the keyway and local shaft diameter changes, but did not apply a stress concentration factor for the fact the bending is applied via the reducer's hollow shaft, which I described as a hub.
This is actually a heavy hollow shaft gear reducer cantilevered on a smallish vertical shaft. Our stress group applied factors for the keyway and local shaft diameter changes, but did not apply a stress concentration factor for the fact the bending is applied via the reducer's hollow shaft, which I described as a hub.
ok, so now you have an axle (shaft) with an overhang(?) and something like a belt-driven wheel on the end so that there are transverse loads applied to the shaft causing bending.
if they've accounted for the key-way (whatever is supplying the shear connection to the shaft) and presumably they've accounted for the bending stresses ... not clear on what you think is the "stress concentration factor for the fact the bending is applied" ...
if they've accounted for the key-way (whatever is supplying the shear connection to the shaft) and presumably they've accounted for the bending stresses ... not clear on what you think is the "stress concentration factor for the fact the bending is applied" ...
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- #11
For what its worth, the 3.25 inch diameter shaft is vertical, and 1000 lb plus of motor is cantilevered 50 inches or so off the shaft cl by the hollow shaft reducer. I believe where the poor vertical shaft emerges from the gearbox's hollow shaft there is a nice "bent over my knee" effect that should be considered.
My dilemma is finding published stress concentration factors for solid shafts in this arrangement (hub / shaft)
My dilemma is finding published stress concentration factors for solid shafts in this arrangement (hub / shaft)
sorry, still stuck on "stress concentration" ...
your picture helps, you've got an eccentric column load on the shaft (i had pictured the shaft as being horizontal).
clearly the load is putting some bending into the shaft, no doubt the flange mount takes this into account.
how is the shaft supported (laterally) ? a lateral couple could react the off-set moment.
but let's assume that the shaft is fixed at it's base. the then moment is introduced at the top, yes ? and reacted at the base, simple enough. so the shaft is reacting the column load and moment, again simple enough; don't see where "stress concentration" comes into it ... there may well be some local plasticity, and maybe you want Zero plasticity at ultimate load ... very conservative design; maybe it's a fatigue problem, but then that hasn't been mentioned.
IMHO, i think you have a situation where the flange mount is applying shear loads into the shaft, and these shear loads apply the column load and off-set moment onto the shaft.
your picture helps, you've got an eccentric column load on the shaft (i had pictured the shaft as being horizontal).
clearly the load is putting some bending into the shaft, no doubt the flange mount takes this into account.
how is the shaft supported (laterally) ? a lateral couple could react the off-set moment.
but let's assume that the shaft is fixed at it's base. the then moment is introduced at the top, yes ? and reacted at the base, simple enough. so the shaft is reacting the column load and moment, again simple enough; don't see where "stress concentration" comes into it ... there may well be some local plasticity, and maybe you want Zero plasticity at ultimate load ... very conservative design; maybe it's a fatigue problem, but then that hasn't been mentioned.
IMHO, i think you have a situation where the flange mount is applying shear loads into the shaft, and these shear loads apply the column load and off-set moment onto the shaft.
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- #13
Sorry for the confusion. The flange in the too-simple drawing has loose fitting pins to react the gearbox torque. (unfortunately) The gearbox flange contributes nothing to supporting the gearbox/motor assembly. The 50,000 lb-in moment is resisted entirely by the shaft. The proportions of the hollow shaft in the gearbox (which is the only useful connection to the vertical solid shaft) would create a pair of several 1000 lb reactions a foot or so apart. This is further enforced by the relief or oversized diameter in the middle third or so of the hollow shaft. If the geometry of the hollow shaft makes it stiff, in the limit each reaction would be applied to the 3.25 inch shaft thru a knife edge.
It runs 24/7 and accumulates 1,000,000 fully reversing cycles every week, so I think I'm justified in being >>very<< concerned about fatigue.
ok, you've got a fatigue question, still having trouble seeing how the moment is transferred into the shaft ... does the shaft have a flange that is captured by the motor housing ? does the motor housing extend over the shaft (like a glove) ? if the latter, wouldn't there be tranverse bolts, so the shaft is loaded by shear loads from the fasteners ? what is the nominal stress level for the fatigue load case ? for the static load case ? what material (presumably steel) ?
Petersen fig164 has a hole in a tube under bending, not too different from a hole in tension ... but if you've got shear loads I think the method from Michael Niu's book (pp232) is most appropriate.
Petersen fig164 has a hole in a tube under bending, not too different from a hole in tension ... but if you've got shear loads I think the method from Michael Niu's book (pp232) is most appropriate.
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- #15
heavy hollow shaft gear reducer slipped onto a vertical shaft
The fixing bolt should be "tightened lightly snug"
The fixing bolt should be "tightened lightly snug"
sorry, but that sounds like a crappy way to transfer an offset moment ... the gear (with the offset load on it) is a loose fit onto the shaft, so the offset moment is being reacted as a transverse couple (where the gear binds onto the shaft) ...
back to the stress concentration question, i don't think this arrangement has a stress concentration factor. there is an effect due to the contact (between the shaft and the gear), but that's more a contact/wear/fretting question.
back to the stress concentration question, i don't think this arrangement has a stress concentration factor. there is an effect due to the contact (between the shaft and the gear), but that's more a contact/wear/fretting question.
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- #17
actually i think your picture shows the point i was trying to make ... the gear is irrelevent to the stress concentration. there is no pad-up to the shaft diamater. there is a keyway which i think is transmitting torque over the loose-fit gear. and somewhere along the line the off-set load comes into play, i think thru contact.
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