fatigue curve creation using ASME VIII Div 2 1

[sencae]

Good Evening To ALL
Can any one please guide me how to create Fatigue Curve with help of ASME VIII Div 2.
Thanks & Regards
Senthil

 

[BenStewart]

The S-N curves can be generated from the equations and data included in Annex 3-F of ASME VIII-2. The use of the Smooth Bar or Welded Joint curves will depend on which location and method you are using to do your fatigue assessment.

 

[TGS4]

FYI - the fatigue curve formulae will be changing in the 2017 Edition (they will be greatly simplified). Unless you have something urgent, I would wait.

There's much more to a fatigue analysis than just an S-N curve, though, as mentioned by BenStewart.

 

[sencae]

Thanks for your reply. From ASME VIII-2 Equation 3.F-1, 3.F-2 & 3.F-3 will give you only one parameter as N. To construct the S N curve we need coordinate for each points(A , B & C) as shown in Figure as example (Refer the attachments).IF I want create Point A I need X value and Y value, similar way Point B & C . How to find X & Y parameters.

 

[BenStewart]

For Smooth Bar - Equations 3-F.1, 3-F.2 and 3-F.3 can all be combined into one equation. All the equation variables, with the exception of stress amplitude (Sa) and allowable number of design cycles (N), are based on the material and which units you are using. Manually tabulate Sa and calculate N, plot the results (log-log and taking note of the stress amplitude limits in the tables) and there's the S-N curve. Alternatively, Table 3-F.9 summarises the S-N curves for the material groups; note, stress amplitude in this table is in ksi.

For Welded Joint - There's another simple calculation method and it's described in 3-F.2.2. Not sure what you're doing but you're instructed to use the date for mean less three standard deviations.

I personally don't know the changes being made for the future Editions, but, regardless, I'd suggest reading the following to get a feel for fatigue analyses using ASME VIII-2:

1. ASME VIII-2 - Specifically, Part 5.5 and Annex 3-F.
2. ASME PTB-1 - There's a good narrative around Part 5.5.
3. This forum - loads of useful information from experiences Engineers.
4. Reliable sources on the internet - as a samples, here's two interesting articles:

https://becht.com/blog/fatigue-evaluation-of-welded-joints,

http://paulin.com/Library/Fatigue_Info/Hinnant_ASME_Plant_Engineering_Presentation.PDF

Hope that helps.

 

[TGS4]

femapwithnxnastran a couple of things...

Your figure indicates an "endurance limit" for steels. The data (from about the early 1990's) shows that such an endurance limit doesn't exist. The slope of the S-N curve is still negative out to 10^11. This has been reflected in the ASME fatigue curves for a while now.

Equations 3-F.1 through 3-F.3, in conjunction with Tables 3-F.1 through 3-F.8 (the C_n parameters come from the Tables), will provide you with the full curve. However, in order to fully implement the curve, you need to know the average temperature of the point of interest over the "cycle". That will provide you with the adjustment necessary, because all S-N curves are actually strain-life curves, and to make them into stress-life curves they need to be multiplied by Young's Modulus, which is a function of temperature.

 

[sencae]

Thanks to all for your guidance and support