Section VI Shaft Design * * Shaft? Shaft Design ASME Shaft

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Shaft Design
Section VI
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Talking Points

• Shaft?
• Shaft Design
• ASME Shaft Equations
• Design of Shaft for Torsional Rigidity
• Standard Sizes of Shafts
• Bending and Torsional Moments

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Shaft?

• Rotating machine element that transmits power.

• Shafts are usually circular in cross-section, and
  may be either hollow or solid.

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Shaft Design

• Consists of the determination of the correct
  shaft diameter to ensure satisfactory strength
  and rigidity when the shaft is transmitting power
  under various operating and loading conditions.

• Design of shafts for ductile materials, based on
  strength, is controlled by the maximum-shear
  stress theory while shafts of brittle materials
  would be designed on the basis of the
  maximum-normal stress theory.

• Shafts are usually subjected to torsion, bending,
  and axial loads.

1) For axial loads The tensile or compressive
stress is
2) For bending loads The bending stress
(tension or compression) is
3) For torsional loads The torsional stress
is
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Shaft Design Cont.
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Shaft Design Cont.
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ASME Shaft Equations

• The ASME code equation for hollow shaft combines
  torsion, bending, and axial loads by applying the
  maximum-shear equation modified by introducing
  shock, fatigue, and column factor as follows

• For solid shaft having little or no axial
  loading, the equation is

Where
Where
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ASME Shaft Equations Cont.
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Design of Shaft for Torsional Rigidity

• It is based on the permissible angle of twist.
  The amount of twist permissible depends on the
  particular application, and varies about 0.3
  degree/m for machine tool shafts to about 3.0
  degree/m for line shafting.

Where
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Standard Sizes of Shafts

• These sizes vary according to material
  specifications and supplier. Typical sizes for
  solid shafts are

• Up to 25 mm in 0.5 mm increments
• 25 to 50 mm in 1.0 mm increments
• 50 to 100 mm in 2.0 mm increments
• 100 to 200 mm in 5 mm increments

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Bending and Torsional Moment

• These are the main factors influencing shaft
  design. One of the first steps in shaft design is
  to draw the bending moment diagram for the loaded
  shaft or the combined bending moment diagram if
  the loads acting on the shaft are in more than
  one axial plane. From the bending moment diagram,
  the points of critical bending stress can be
  determined. The torsional moment acting on the
  shaft can be determined from

1) For belt drive The torque is found by
2) For gear drive The torque is found by
Where
Where