fatigue life for metal bellows

[Zerafin]

Hello everyone,
I 'am studying EJMA code for some time already and I need some help regarding the fatigue life calculation.
Can someone please tell me how to determine the ''material and manufacturing constants a,b and c''? from the formula in the link? you can also see it here. ''Nc=(c/St-b)^a''.
The think is that I found something about this ''a,b,c'' constants in EJMA 9th version, but is for high temperature conditions and in my case I have no high temperature and no pressure for my metal bellows application. Once I have the bellows I need to test them, therefore I need a testing plan and also some formulas to be able to find the constants ''a,b,c'' . Any help would be great.
thank you in advance

 

[SnTMan]

Zerafin, I have no idea what you are doing with your bellows, but from my experience in pressure vessel work, the selection of values for various constants is per each manufacturer and is, well, not 100% transparent.

You might consider supplying your design conditions to a manufacturer or two and see what cycle life they calculate. To further muddy things you may see "EJMA" cycles and "ASME" cycles.

Regards,

Mike



The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Zerafin]

Thank you for your interest in my post SnTMan. But your answer is not helping me at all. I need to make these testing's and to calculate the coefficients ''a,b and c'' as per EJMA code.
My application for witch I am using metal bellows is a company secret for he moment. But yet I wish that someone can explain me how to get data from a series of metal bellows testing's.
In EJMA they say something about a H (hold time between cycles) witch they use in formulas to determine the constants ''a, b and c''.But I am not sure what this ''H'' coefficient means. I was thinking maybe is about how fast a cycle extension-compression runs, when I am testing a metal bellows.
If is someone ho made fatigue calculations for metal bellows please advice me.