Fatigue Curves Equation 3-F.1 What is E3? 1

[goCoogs]

I'm working on the fatigue analysis screening. I'm stuck on equation 3-F.1. It has a variable E3 that I can't find referenced anywhere as to what it symbolizes. Can somebody help me out? I tried just using the curves, but I want to double check myself using the equations. I appreciate the help.

 

[TGS4]

Exponent. It means x10^3. 4E3 is another way of writing 4,000. 4E6 means 4,000,000.

 

[goCoogs]

Ah, that makes sense. I've just never seen it written with a space between the coefficient and the E. 4E3 vs. 4 E3
Thanks for the clarification!

 

[tigny]

Hi,

In version 2017 of the code, isn't there an error in the formula (3-F.1) of ANNEX 3F?

Y = (S_a/C_US).(E_FC/E_T) (3-F.3, 2015)

Y = log[28.3 E3(S_a/E_T)] (3-F.1 2017)

Even though the Y factor may not be "the same", it seems that in the 2017 version 28.3 E3 is E_FC in ksi units, which was corrected for SI units by the C_US term in version 2015.
So in version 2017, isn't there a problem with units?

In version 2017, a C_us for units of stress in MPa term has disappeared.
Is there something wrong in this ANNEX?

 

[TGS4]

Nothing wrong. That's the value of Young's Modulus in ksi.

 

[tigny]

Hi,

... Young's Modulus in ksi

Then, in in SI units calculations, shouldn't we use 195.0 E3(S_a/E_T) instead of 28.3 E3(S_a/E_T) for calculating Y in (3-F.1) or (3-F.6)?

[ul]
[li]If not, what is the Table 3-F.1 used for?[/li]
[/ul]

best regards,

 

[TGS4]

Yes, you would use the values in that table. Looking at the wording again, we may not be as clear as could be. I'll check tomorrow to see if there's already been a Code item to fix that. If not, there's probably time before the deadline for 2019 to get it fixed.

 

[BJI]

No, Sa/Et is unitless, so it doesn't matter what units you are using, Y will always be in US Customary, and the equations for X are based on US Customary, therefore you should not change equation 3-F.1 regardless of the unit system you are using.

The curves however are presented in both units, therefore you need to use Table 3-F.1 to adjust the results appropriately when using the figures only.

It isn't obvious at first, particularly if you are comparing the two code releases but the equations are correct.

 

[tigny]

TGS4, BJI,

thank you for your explanations.
Yes I think a sentence about use of units in this section would help.

 

[NRP99]

It is creating confusion for SI unit users. The equation 1 is interpreted along with the Table 3-F.1.