So Far So Good
Don't forget the deflection check though! ■
John Gateley johngateley@hotmail.com www.the-credible-bulk.com
Clarification
Dear Sir,
perhaps you could make up a sketch of how you imagine the turndown of the shaft in question. If it is a stepped shaft meant by the expression, there's "stress - raisers" to be considered and a picture of the situation would be welcome. Perhaps you could add the loads and the way you apply them in your calculation model?
Thank you in advance
Regards
R. ■
Re: Calculating Stresses At Shaft Turndowns
Hello,
Maximum stress in the shaft of drive pulley occurs at the centre of the hub, nearest to the drive end. The torsional stress value, from drive end to this hub centerline, remains same for all sections of the shaft in this zone. Whereas bending moment value is zero at bearing centerline and it is maximum at the aforesaid hub centerline.
You are using the shaft design formula which takes into consideration torsion as well as bending. You can apply this formula for any section of the shaft, by calculating the applicable torsion as mentioned above and the bending moment occurring at that section.
As said in earlier reply to thread, also check for shaft deflection at hub due to radial loads.
The applicable formula is simply supported beam subjected to symmetrical twin load. The shaft allowable deflection value could be in the range of 5 to 8 minutes, for keyed shaft, depending upon application / choice. The shaft diameter between hubs will be to suit deflection, but not less than shaft diameter at hubs (sometime designer makes it 1 or 2 mm less due to assembling or other reason, which is okay).
Regarding shear stress and bending stress you can consider safety factor on yield / endurance strength or directly use allowable stress as per the formula you are using.
The issue of stress concentration can be addressed by providing gradual taper from one diameter to next diameter.
Ishwar G. Mulani
Author of Book: Engineering Science And Application Design For Belt Conveyors (new print November, 2012)
Author of Book: Belt Feeder Design And Hopper Bin Silo
Advisor / Consultant for Bulk Material Handling System & Issues.
Pune, India.
Tel.: 0091 (0)20 25871916
Email: conveyor.ishwar.mulani@gmail.com
Website: www.conveyor.ishwarmulani.com ■
Calculating Stresses at Shaft Turndowns
Good day All
Considering a drive pulley shaft, it is subjected to both bending and torsion. How would you calculate the stresses at the turndowns?
This is how i approached it:
1. Calculated the stress concentrations at the turndowns for both bending and torsion
2. Since the shaft is under bending and torsion, I calculated the combined effect to obtain combined bending and combined torsion values
3. Calculated the stresses (torsion and bending) at the turndowns using the values obtained in (1) and (2)
Is this approach correct?
Furthermore, what would be the max allowable stress when checking the stresses calculated at the turndowns. I'm assuming 55MPa as it is what is used when calculating the shaft diameters.
Regards
Ranwedzi ■