selecting shaft diameter.

[Liquid]

I have a steel shaft subjected to a maximum bending moment of M, and a torque of T. Its UTS is 430MPa, and its USS is 340. I need to find out the minimum diameter of this shaft.

Can anyone guide me through the process please?

 

[boo1]

use the elastic torsion formula
outside allowable surface stress=(torque*radius)/polar moment of inertia

J=(Pi/2)*(Rad**4)

 

[GregLocock]

Liquid's shaft isn't in pure torsion, he's also got bending.

Think Mohr's circle.




Cheers

Greg Locock

 

[Gasbat]

Hi!

I think you should have to calculate the diameter under two points of view: static and dinamic (fatigue).

Surely the fatigue criterium will be more restrictive but it could be too long to describe the method here and there are a lot of books that explain it very well.

The static criterium (von Misses) for circular shafts under flexion (M)and torque (T) is:

D^3=16/(Pi*USS)*SQR(4M^2+3T^2)

Bye!

 

[dvd]

Machinery's Handbook has some simple formulas for shaft sizing. But most of the shaft sizing formulas fall down in that they don't take into account the shaft speed. You also can find simple shaft critical speed formulas in Machinery's Handbook. Or you can calculate by taking the square root of the (deflection divided by g). Lots of shafts sized by formulas which only consider the bending and torsional moments fail, or cause other components to fail because of shaft whip.

 

[asmenut]

I agree with Greg, If you are looking for static conditions of both Axial and Torsional loads, Mohr's Circle will be of great benefit. Once you have the shaft sized, then GasBat's static criterium formula will help to verify and fine-tune. But remember that depending on the application, a vibrational might not hurt either.

 

[manuvisravas]

better u refer design data book , under the topic of "SHAFTS SUBJECTED TO BENDING MOMENT".
BYE FRIEND.

 

[dvd]

Also don't forget to consider that if the shaft has a keyway there will be additional stress concentrations.

 

[MAzi]

any recommendation regarding design of pressure vessels external attachments : lugs, rings, etc. ? or any ref. how energy method is applied to such cases?
HINT: pls. don't mention D.R. Moss (actually i recoomend not to rely much on coefficient tables in 2nd. ed. due to too many typing errors - e.g. compare tables 3-11, -12 to 5-9 & 5-10). . . thanks.