# Help with roarks nomecular

1. Oct 7, 2009

### kieren12345

I have an old book on roarks formulas for stress and strain. Which seams to have the formulas I need but it doesnt have explaination of what the variables are. I am a mechanical engineer but have not studied Roarks.

Does anyone know the following?
b/a
ro/a
yb
mrb
ya
mra

Thanks

2. Oct 7, 2009

### Mech_Engineer

I think you mean "nomenclature."

It's impossible to tell you anything about the variables you have listed without seeing the equation in which they are presented.

3. Oct 7, 2009

### kieren12345

Thank you for correcting me there.

the formula I have is
yb=0
0b=0
ya=0
0a=0

mrb=-wa(C3L6-C6L3)/(C2C6-C3C5)
Qb=w(C2L6-C5L3)/(C2C6-C3C5)
mra=MrbC8+QbaC9-waL3
Qa=Qb(b/a)-(wRo/a)

any help?

4. Oct 7, 2009

### FredGarvin

Please list the table or section to which you are referring.

5. Oct 7, 2009

### Q_Goest

It would help to see what section (and edition of the book) you're referring to, but it looks like a flat, circular plate.

b is a radial dimension (see figure in book)
a is a radial dimension (see figure in book)
so b/a is a ratio of the radial dimensions.
ro is also a radial dimension (generally to a line of load)
mrb refers to a radial moment at b
mra refers to a radial moment at a

mrb=-wa(C3L6-C6L3)/(C2C6-C3C5)
C2, C3, C5, C6, L3, L6 are all constants. There will be a table for these constants at the beginning of the table you're looking at for the specific geometry.
etc...

If you can be more specific (what table are you using, what edition of the book, etc) it would help.

6. Oct 7, 2009

### kieren12345

thanks

to explain abit better. I have two circular plates that is bolted to an internal and external ring, so that there is a cavity inbetween. We are giong to pressurise this cavity to 10bar and see how an internal elastomer reacts. One of the end plates is steel and one is plexiglas.

Please see 2nd attachment for drg.

7. Oct 7, 2009

attached

8. Oct 8, 2009

### CFDFEAGURU

Kieren12345,

Nothing is attached.

I use Roark's book about once a week. All the C's and other constants can be confusing.

At the Roark website there is an online calculator. I have never used it so make sure you run some test cases and verify with some hand calcs that the program is producing the correct results.

http://www.roarksformulas.com/

Thanks
Matt

9. Oct 8, 2009

### Q_Goest

This is a good point, I meant to bring it up. If you do the calc per Roark, you might consider posting your input, the case used, and the output. It's easy enough for people that use Roark to verify your calculations are correct. I have spreadsheets for many of the circular plates and also access to all the cases on Mathcad.