Calculating Inside Diam. & Stress of Hollow Steel Shaft

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Discussion Overview

The discussion revolves around calculating the inside diameter, outside diameter, and stress on a hollow steel shaft given specific torque and torsional shear values. It includes aspects of homework-related problem-solving and mathematical reasoning.

Discussion Character

  • Homework-related
  • Mathematical reasoning

Main Points Raised

  • One participant presents a problem involving a hollow steel shaft with given torque and shear stress, seeking to find the inside and outside diameters as well as the stress on the inside of the shaft.
  • Another participant provides a formula relating shear stress to torque and polar moment of inertia (J), indicating that shear stress can be calculated as Tr/J.
  • A participant confirms that they have substituted the values for J and r in their formula but expresses uncertainty about the correctness of their approach.
  • One participant questions whether the J used is for the inner diameter and notes that their calculated stress exceeds the given shear stress, suggesting a potential issue with their calculations.
  • Another participant reiterates the formula for J specific to hollow shafts, indicating that J is calculated using the outer and inner diameters.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the correct approach to calculate the stress on the inside of the shaft, with some expressing uncertainty and others providing differing interpretations of the formulas involved.

Contextual Notes

There are unresolved aspects regarding the assumptions made in the calculations, particularly concerning the definitions of J and the diameters used in the formulas.

darkmagic
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Homework Statement



Given:
hollow steel shaft
Torque = 5400 Nm
Torsional Shear = 150 MPa

Required:
Inside diameter
Outside Diameter
Stress on the inside of the shaft

Homework Equations





The Attempt at a Solution


I solved both the diameters which are 64.49 mm and 48.37 mm.
I don't know what formula to use to determine the stress on the inside of the shaft

I used to 16T/[pi d^3) where d is the inside diameter. Am I correct?
 
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T/J = (shear stress)/r

so shear stress = Tr/J

at the outer, r = outer radius

at the inner r = inner radius
 
The J and r are already substituted in the formula I used. Ok thanks.
 
Is J there the J of the smaller circle, with the inside diameter? I got 243 Mpa which is larger than 150 Mpa.
 
darkmagic said:
Is J there the J of the smaller circle, with the inside diameter? I got 243 Mpa which is larger than 150 Mpa.

Your shaft is a hollow one, so the J = (π/32)(douter4-dinner4)
 

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