Can rotating shafts experience changes in deflection due to inertial effects?

In summary, the conversation discusses the deflection of a shaft due to rotation and how it differs from a stationary position. The force diagram and images show the locations of the rotational fixture and applied force. It is mentioned that in a fixed direction force, the deflection will remain in the horizontal plane between two pulley shaft centerlines, but if the force rotates, the deflection will also rotate. The amount of deflection will be the same in both cases. It is then clarified that rotational inertia will not affect the deflection of a rotating rod compared to a stationary rod, and that in more demanding applications like jet engines, inertial effects must be considered in design. These effects include whirl, torsion wise instability, inertial stiffening
  • #1
Spectre
2
0
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
 
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  • #2
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.
 
  • #3
JBA,
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?
 
  • #4
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.
 
  • #5
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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1. What is deflection in a dynamic shaft?

Deflection in a dynamic shaft refers to the bending or flexing of the shaft when it is subjected to external forces or loads.

2. What causes deflection in a dynamic shaft?

Deflection in a dynamic shaft is caused by the applied forces and moments that act on the shaft, such as torque, weight, and vibration.

3. How is deflection in a dynamic shaft measured?

Deflection in a dynamic shaft can be measured using instruments such as strain gauges, displacement sensors, and accelerometers.

4. What are the effects of deflection in a dynamic shaft?

Deflection in a dynamic shaft can cause changes in the alignment of the shaft, increase in stress and strain, and ultimately lead to failure if not properly controlled.

5. How can deflection in a dynamic shaft be minimized?

To minimize deflection in a dynamic shaft, engineers use techniques such as increasing the shaft's diameter, changing the material, and adding supports or bearings at key points along the shaft.

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