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roarks ebook 6th edition: constant for case 17b correct?

JXBWk
13-Aquamarine

roarks ebook 6th edition: constant for case 17b correct?

To all

In mcad Roark's e-book 6th edition there is a worksheet to calculate the stress concentration (case 17b).

I just noted that the constants to calculate the values for C1, etc are different to the ones in the latest book (Petersons 3rd edition)

1. Am I correct?

2. I cannot find a 1974 copy 1st edition (I guess!)  which appear to be the reference used. Has anyone got access and could confirm?

3. Is it the same in the latest ebook which I think is based on Roark's 7th edition but as far as I can tell in the printed Roark's 7th edition the numbers are from the 1974 edition too

 

Thanks

Regards

17 REPLIES 17
Fred_Kohlhepp
23-Emerald I
(To:JXBWk)

My printed 4th edition doesn't have a case 17 . . . (jumps from 16 to 18,  ???)

 

My previous experience with the Roark ebook (under the original Mathcad owners) was that it had been farmed out to an intern as a project so they could improve their Mathcad skills; the information was (mostly) correct but the programming was stilted, plots were usually vectors not functions even though functions were used to calculate the vector values.

Given your choices I would choose (in preference order):

  1. Peterson
  2. Printed Roark
  3. your best guess
  4. Roark ebook.

If you post your problem geometry (not just a table reference) I'll try to help further.

 

Good Luck!

JXBWk
13-Aquamarine
(To:Fred_Kohlhepp)

Thanks. I set-up the Kt calc as per Petersons 3rd edition and for my geometry I got 2.65. the formula in Roark's ebook gave me 2.64. So not going to lose sleep

The geo is irrelevant (but thanks for the offer) I am more concerned about the factors and the discrepancy

 

Werner_E
24-Ruby V
(To:JXBWk)

Not my area of expertise at all, but the table in the seventh edition I found here

http://materiales.azc.uam.mx/gjl/Clases/MA10_I/Roark%27s%20formulas%20for%20stress%20and%20strain.pd...

seems to correspond with the formula in the Mathcad sheet:

Werner_E_0-1612534928294.png

 

JXBWk
13-Aquamarine
(To:Werner_E)

but as fas as I can see the constants in the calculation of the C values are not the one in Peterson 3rd edition

Converted to functions in Prime 4.0

You may consider creating a variable name like "h/r"

Werner_E_0-1612555287351.png

 

😊

 

Yeah, I was in a rush, I don't think cntrl-shift-K works in Prime, so I'd have to type it in text, copy it, then paste it everywhere I needed it.  so h_r is type-able.  (Remember--I'm a lazy engineer!)

 

BTW, isn't it strange how the C's change so abruptly between regions?  (Except for the first!)

Fred_Kohlhepp_0-1612558535464.png

 



BTW, isn't it strange how the C's change so abruptly between regions?  (Except for the first!)

 


I am too far out of my comfort zone - even to make an educated guess. But at least I can say that its remarkable.

Empirical formulas ofton follow their own intrinsic logic and as along as we don't know how exactly they were arrived at ...

But i think that the values of the various C's are not that critical - but I would expect the cubic K.t to be nice and smooth without obvious crincles. But then, I may be wrong.

Empirical formulas often follow their own intrinsic logic and as along as we don't know how exactly they were arrived at ...

But i think that the values of the various C's are not that critical - but I would expect the cubic K.t to be nice and smooth without obvious crincles. But then, I may be wrong.

 

You're not wrong:

Fred_Kohlhepp_0-1612598759923.png

 

VladimirN
24-Ruby I
(To:JXBWk)

7th Edition:

 

7th Edition.png

 

8th Edition:

 

8th Edition.png

 

P.S. Years of edition (from 9-th to 1-st): 2020, 2012, 2002, 1989, 1975, 1965, 1954, 1943, 1938.

as per the original poster question I had a look at my copy of Petersons and indeed it seems that the constants defined in the C values are different - see attached Chart 3.10 from Peterson

The Roark's data seems to be pointing to the 1st edition of Peterson

 

@JXBWk The difference appears to be academic in this case - see graph attached (an "issue" at t/r = 2.0 possibly but I may have a made a mistake in typing the numbers!) but I get your point. One difference also is that the 1st set of C values are for 0.1 <= t/r <= 2.0 where in Roark's it is for 0.25 <=t/r<= 2.0

JXBWk
13-Aquamarine
(To:JBlackhole)

Peterson's also gives an equation for Kt bending, eq 3.7 - taken from Tipton et All (see attached), but if I "code" it get an imaginary number out of it !!

Tried with D = 200, d=100, r15 and I get 0.65+0.479i

Obviously does make sense - What I am doing wrong?

 

Werner_E
24-Ruby V
(To:JXBWk)


@JXBWk wrote:

Peterson's also gives an equation for Kt bending, eq 3.7 - taken from Tipton et All (see attached), but if I "code" it get an imaginary number out of it !!

Tried with D = 200, d=100, r15 and I get 0.65+0.479i

Obviously does make sense - What I am doing wrong?

 


How could we tell if you don't show what you did?

My best guess is that you typed 0.503*(d/D)^4 instead of 0.503*(D/d)^4.

The formula gives you real values as long as |d/D| is greater or equal to 1 and in your case D/d=2, so all seems to be OK.

Werner_E_0-1612792133457.png

 

 

 

 

JXBWk
13-Aquamarine
(To:Werner_E)

Fair enough - Was still thinking about what I was writing in mcad when I asked the questing. Must have overlooked as I did attach the equation!

 

Werner_E
24-Ruby V
(To:JXBWk)


@JXBWk wrote:

Fair enough - Was still thinking about what I was writing in mcad when I asked the questing. Must have overlooked as I did attach the equation!

 


Wow! Looks like my freshly polished crystal ball did a good job 😉

Werner_E_0-1612793973607.png

 

 

Fred_Kohlhepp
23-Emerald I
(To:JXBWk)

Hmmm!

Fred_Kohlhepp_0-1612791813473.png

File of original Kt with your equation appended (Prime 4) attached.

JXBWk
13-Aquamarine
(To:Fred_Kohlhepp)

Clearly I am an idiot who cannot make the difference between D/d and d/D !

I typed 0.503(d/D)^4 instead of 0.503(D/d)^4

 

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