How Do You Calculate the Optimal Shaft Diameter to Avoid Fatigue?

[WildFlower]

Hi, I have been atempting this is a question for a week now and I've been struggling on the final part. The question is below in bold.

The tension in a flat belt pulley is 1250N when stationary. Calculate the tension in each side, and the power transmitted, when the belt is on the point of slipping on the smaller pulley wheel. The wheel is 240mm diameter and the coefficient of friction is 0.320. The angle of lap is 165 degrees and the wheel speed is 1500 RPM.

If the shaft protrudes from the motor by 100mm., determine a suitable shaft diameter, manufactured from the same material as in question 18 above- the shaft MUST NOT suffer from fatigue at all - that is, it must have an indefinite life span.

The material that is mentioned in the question can be found at htttp://www.specialmetals.com/products/inconelalloyx750.htm and is figure 12.

I have answered the first part of the question and got a power of 20.297 KN and using KSI = Stress/6.894757E-6 I got a value of 268.89MNM2. The tension in each belt came out to be 1788.4 N and 711.6 N.

It is the second part of the question I have been struggling with. I think I would have to use Bending moments to calculate when the material would fail but even then I would not know what diameter the shaft should be. Plus I'm not totally sure If I have enough information to work out the maximum bending moment.

Could anyone give me any pointers and/or suggest where I'm going wrong and what I should be doing as an alternative.

 

[Analysis]

shaft diameter,fatigue

Yes you are correct you have to use bending moment equation.
From this bending moment equation you can derive shaft diameter.
Ref.text books shigely etc
Regarding fatigue i have attached one material go through that you can have idea.
Thank u
Prakash

 

[WildFlower]

Thanks for the help.The attachment is pending aproval. But there should be enough information on these two sites for me to answer the question?

http://musr.physics.ubc.ca/~jess/sci1/biol/beamtheory/node1.html

http://physics.uwstout.edu/StatStr/statics/Beams/beam41.htm

 

[darbyshire91]

i am trying to do the same question and like you had done i have performed the first part but i am stuck on the second these websites do not work anymore. do you have any alternatives?

http://musr.physics.ubc.ca/~jess/sci1/biol/beamtheory/node1.html

http://physics.uwstout.edu/StatStr/statics/Beams/beam41.htm[/QUOTE]