Stress' in rotating discs. HELP

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Discussion Overview

The discussion revolves around the analysis of stress in a rotating disc, specifically focusing on determining the maximum angular velocity for a solid disc made of 440c material with a diameter of 6.75 inches. Participants also explore the quantification of stress concentration due to radial holes in the disc.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • The original poster is analyzing the maximum possible angular velocity of a solid disc and has provided specific material properties and dimensions.
  • There is uncertainty regarding the use of ultimate tensile strength versus Young's modulus (E) in calculations, with the poster noting that using E yielded more reasonable results.
  • One participant questions the assumption of "realistic" speeds and suggests that the loading from the holes may not have been fully considered in the problem statement.
  • The original poster clarifies that the holes are blind and tapped but do not have anything screwed into them, indicating that the disc has been tested at higher speeds than calculated using ultimate stress.
  • Another participant references external material that appears to align with the equations being used, questioning the basis for the original poster's claim that their results were significantly lower than expected.
  • The original poster expresses appreciation for additional resources that provide more complexity regarding stress distribution in the disc.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the validity of the calculations or the definition of failure, and multiple viewpoints regarding the stress analysis and assumptions remain present.

Contextual Notes

There are unresolved questions about the assumptions made regarding stress distribution, the definition of failure, and the impact of the blind holes on the overall stress analysis.

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Stress' in rotating discs. HELP!

I am working on an independent project where I am analyzing the maximum possible angular velocity of a solid disc of a given diameter and material.

The Diameter is 6.75"

Material is 440c
E= 29,000 Ksi
Density of .275lb/in^3
Ultimate tensile strength: 294,426 Psi (294Ksi)

How fast can this rotate?

Part2:

How do I quantify the stress concentration of RADIAL holes in this disc? I have found numerous papers on eccentric holes but not radial on the periphery. Holes are blind and tapped.

Maximum speed should be around 40K-60K RPM.

I have been using these formulas:

https://www.physicsforums.com/latex_images/14/1425557-0.png

https://www.physicsforums.com/latex_images/14/1425557-1.png

I have taken R to be zero for radial stress (the center)
and 3.375 for tangential stress.

I originally used the ultimate stress and solved for omega, but those results were 10x lower than realistic.

So i used E, and the results seem reasonable. Although I am not sure WHY I had to use E or if this was the right thing to do.

Can I get some assistance? Thanks.
 
Last edited by a moderator:
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You say that the holes are blind and tapped. That suggests that you plan to screw something into these holes, and if you do, that is going to load the periphery of the disk. Have you left something out of the problem statement?

You say that when you solved for omega it was "10x lower than realistic." How do you know what is realistic?
 


Nothing screws into the holes.

The disc actually exists, so I have seen it go faster than the original numbers that resulted from using the ultimate stress.
 
Last edited:


Did a search and came up with this
http://www.utm.edu/departments/engin/lemaster/Machine%20Design/Lecture%2016.pdf

Looking through here, it looks like your using the same equations though. Why do you think your results are 10x too low? Experience? What are you defining as failure?
 
Last edited by a moderator:


Ahh, thank you Minger. There is more there than I had before, a lot more.

Particularly the graphs. I had assumed radial stress to be at a maximum in the center, and tangential to me at maximum on the OD but it seems more complex than that.
 


anyone?
 

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