What Causes Discrepancies in Calculating Shearing Stress in a Circular Shaft?

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SUMMARY

The discussion centers on calculating the maximum shearing stress in a circular shaft subjected to a torque of 120 ft-lb. The correct formula for shearing stress is given as τ = Tr/J, where T is torque, r is the radius, and J is the polar moment of inertia. The initial calculation yielded an incorrect value of 1448 psi due to a failure to convert torque units from ft-lb to in-lb. After correcting the unit conversion, the accurate maximum shearing stress is determined to be 17.39 ksi.

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  • Understanding of shearing stress calculations
  • Familiarity with torque and its units
  • Knowledge of polar moment of inertia (J) for circular shafts
  • Basic unit conversion techniques
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  • Review the derivation of the polar moment of inertia for different cross-sectional shapes
  • Learn about unit conversions in mechanical engineering, specifically for torque
  • Explore advanced shearing stress analysis in composite materials
  • Investigate the effects of varying shaft lengths on shearing stress calculations
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Hey guys, I got a problem that goes like: A shaft with a circular cross section is subjected to a torque of 120ft-lb. Its shaft's diameter is 0.750 in and its length is 15 in., determine the maximum shearing stress.

I did the following: I tried to use shearing stress = Tr/J in which i plugged in as followed (120*.750/2)/(pi/32)*.750^4 and i get 1448, but the answer should be17.39ksi. I assume i am not getting the right answer because I am not factoring in the length but I am not sure. Any help is appreciated, thanks
 
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nm, i figured it out, Stupid me forgot to convert the ft-lb to inch-lb.
 

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