# Stress' in rotating discs. HELP

1. Mar 27, 2009

### Vr6Fidelity

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 [Broken]

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

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: May 4, 2017
2. Mar 27, 2009

### Dr.D

Re: Stress' in rotating discs. HELP!!

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?

3. Mar 27, 2009

### Vr6Fidelity

Re: Stress' in rotating discs. HELP!!

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: Mar 27, 2009
4. Mar 30, 2009

### minger

Re: Stress' in rotating discs. HELP!!

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

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: May 4, 2017
5. Mar 30, 2009

### Vr6Fidelity

Re: Stress' in rotating discs. HELP!!

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.

6. Apr 10, 2009

### Vr6Fidelity

Re: Stress' in rotating discs. HELP!!

anyone?