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Deflection in a Dynamic Shaft

  1. Mar 30, 2017 #1
    I am curious how the deflection of a shaft changes due to rotation. In the force diagram image the green arrows show the rotational fixture locations and the purple arrow show the location of the applied force. The second image shows the deflection during a static test. If the force is applied from a stationary position, how would the amount of deflection change due to the rotation of the shaft along is axial axis? Does a rotating shaft deflect less than a rotations shaft? Shaft Force Diagram.jpg Shaft Deflection.jpg
  2. jcsd
  3. Mar 30, 2017 #2


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    If the static force were applied from a fixed direction, as with a pulley being loaded by the tension of a belt attached to another pulley then the deflection would remain in the horizontal plane between the two pulley shaft centerlines; on the other hand, if the force rotates about the shaft as if the the pulley had a weight attached at some point on it circumference then the deflection will rotate with the weight. Either way the amount of deflection will be same in both cases.
  4. Mar 31, 2017 #3
    This issue is a fixed direction force due to a belt running around a rod as you state in your first example. Just to clarify, rotational inertia would have no affect on decreasing the deflection of the rotating rod compared to the deflection on a stationary rod?
  5. Mar 31, 2017 #4


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    No it will not have any effect, the main effect will be full stress reversal fatigue on the shaft, so a fatigue life evaluation based upon the maximum bending stress would be in order as apart of the design.
  6. Apr 1, 2017 #5


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    Just for general interest :

    In more demanding applications like jet engines inertial effects do have to be considered in design of the rotating components

    The most common effects are :

    Whirl .
    Torsion wise instability .
    Inertial stiffening .
    Gyro deflection .
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