Question about the safety factor for a shaft diameter

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    Diameter Safety Shaft
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SUMMARY

The discussion centers on determining the appropriate safety factor for a turbine shaft diameter using Aluminium 6061, which has a yield strength of 48 MPa, tensile strength of 115 MPa, shear strength of 83 MPa, and fatigue strength of 62 MPa. The participants agree that the yield strength should be used for calculations due to the ductility of Aluminium 6061, as exceeding this value would lead to permanent deformation. The formula for the factor of safety (F.O.S) is confirmed as Max load divided by Load applied, emphasizing the importance of selecting the correct strength parameter to ensure the shaft's functionality.

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  • Understanding of mechanical properties of materials, specifically Aluminium 6061
  • Knowledge of stress-strain curves and plastic deformation
  • Familiarity with the concept of factor of safety (F.O.S)
  • Basic principles of turbine design and load calculations
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  • Research the mechanical properties of Aluminium 6061 in detail
  • Study the implications of plastic deformation in mechanical design
  • Learn about calculating the factor of safety for different loading conditions
  • Explore design considerations for turbine shafts under varying operational loads
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Mechanical engineers, materials scientists, and turbine designers seeking to optimize shaft design and ensure structural integrity under operational loads.

Arnsol
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Hello,

So we are designing a turbine. We have a shaft that receives 710W / 13.6NM / 500RPM from the runner and we are going to 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 can't wrap my mind around which of those i should use. First thought is going with the 48 MPA yield since aluminium is ductile?

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Any thoughts? I am so confused...
 
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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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Thank you.Yes, its the ultimate strength... But it makes sense to me to chose the yield value.
Regards
 

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