Question about the safety factor for a shaft diameter

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  • Thread starter Arnsol
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  • #1
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Homework Statement:

w

Relevant Equations:

See attepmt
Hello,

So we are designing a turbine. We have a shaft that recieves 710W / 13.6NM / 500RPM from the runner and we are gonna find a diameter with safety factor of 3.
Take the following information regarding metal:
Aluminium 6061
Tensile strength115 MPa
Yield strength48 MPa
Shear strength83 MPa
Fatigue strength62 MPa
i know F.O.S = Max load / Load applied.

Still i cant wrap my mind around which of those i should use. First thought is going with the 48 MPA yield since aluminium is ductile?

1585139154452-png.png

Any thoughts? im so confused...
 

Answers and Replies

  • #2
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I would agree with you on that. Once you surpass the yield strength you enter the "plastic region" of the stress-strain curve. This means that once the load is released the metal will not return to its original dimensions, and therefore no longer function as designed.

I think what the chart is referring to as "tensile strength" is also called "ultimate strength". This value is way into the plastic region and you would not want the shaft to reach this value.
 
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Likes Lnewqban
  • #3
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Thank you.Yes, its the ultimate strength... But it makes sense to me to chose the yield value.
Regards
 

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