Fracture Toughness for Cast Iron 2

[MER3]

I am trying to apply the Paris Equation to some cast iron piping and coming up short on the fatigue properties. Everything I can find is for steel. Does anyone have a good resource for cast iron fatigue? I found one paper with some values for fracture toughness but I'd like to see if anything else is out there.
Thanks

 

[TugboatEng]

Cast iron is a poorly defined material with a wide range of properties that may not be consistent.

 

[MER3]

Yeah I know, but if is there anything at all on it? I have ASTM specs for the material, does that narrow the search down at all? Even a range of values just to try to get in the ballpark.

 

Cast iron doesn't lend itself well to reliable fatigue analysis. Charpy impact toughness is usually quite low. In fact you can consider gray iron to be pearlite and ferrite with many many well distributed stress raisers.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[bcd]

From my old machine design textbook (Faires; Design of Machine Elements, 4th edition):

Reversed bending gray iron 0.4 Su < Sn < 0.6 Su

The endurance limit (Sn) in reversed bending is between 40 to 60% of the ultimate strength.

It gives the following endurance limits for these gray irons:

ASTM 20: 10 ksi
ASTM 30: 12 ksi, 16 ksi at 1 million cycles, 21 at 100,000 cycles
ASTM 35: 16 ksi
ASTM 40: 18.5 ksi
ASTM 50: 21.5 ksi
ASTM 60: 24.5 ksi

 

[Tmoose]

Values similar to bdc's ( except in quaint British tons/square inch) here -

https://books.google.com/books/about/Cast_Iron.html?id=gb8TAAAACAAJ

 

[Gary J Melanson]

Not sure if this helps. I have included an attachment regarding fatigue on cast iron.

 

[Tmoose]

I accidently referred to bcd as bdc in my Jan 24 post.

Sorry.

Dan T

 

Your header states fracture toughness but then you ask about fatigue. There's no relationship between those two for any material (although I deal with many materials engineers who insist on confusing them).

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[MER3]

I am primarily interested in the fracture toughness for use with the Paris Equation, which according to my understanding is an equation for predicting the growth rate of a fatigue crack. Fracture toughness is used to calculate the crack size at fracture, which is one of the limits of integration in the Paris Equation. If there is a better way to word the question I would be glad to hear it. I am not very experienced with this topic.

 

You have it right.
Fatigue (or possible other progressive mechanism) takes you to the critical crack length, then fracture toughness takes over.
It's just that with cast iron both those things are difficult to characterize with reliable precision.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[MER3]

That is the impression I am getting. Are there any studies at all that you are aware of?

 

No. I stay pretty much empirical; even more so for cast iron. The main reason being that components in complex real-world environments do not fail in the same way that idealized coupons fail in simplified laboratory tests. They are very useful for ranking candidate materials for design and for validating products.

I would say that if you are at the point where you need to assess the fatigue strength and fracture toughness of a material that is distinctly lacking in both, it may be time to consider a better material.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[WKTaylor]

M3... You have asked us to address a very generic/non-specific issue.

You have not been specific regarding 'what IRON/iron-alloy' per 'what specification', intended to perform in 'what environment'... that You are interested in, so we can REALLY help.. not teach...

Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[replica]

This is a little bit out of topic..... Is there any beach mark (fatigue striation) on cast iron fracture surface. Anyone who has any experience looking at it? Can we see striation on ductile cast iron?