yield strength reference 0.2 or 0.6% offset 2

[Tmoose]

Every reference I have, some dating back to the 60s, seem to use a 0.2% offset when specifying yield strength.

Some steel certs have been coming through recently also list yield at 0.6% offset.

Even Google comes up empty so far regarding why, when or who might prefer this.

(One of these Mill test Certificate spec sheets also says the macro structure must have no visible "crackles" per ASTM E381)

 

[EdStainless]

Some specs (read EU) require yield at various offsets. recently I have seen both 0.2% and 0.5% listed on some certs.
Just make sure that your purchase spec spells out "0.2% offset Yield Strength".

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[TVP]

Regarding ASTM E381, crackles is probably a poor translation from a different language. Here is an excerpt from E381 that describes what macroetching can reveal.

Macroetching will show: (1) variations in structure such
as grain size, dendrites, and columnar structure; (2) variations
in chemical composition such as segregation, coring, and
banding; and, (3) the presence of discontinuities such as laps,
seams, cracks, porosity, bursts, pipe. and flakes.

There are also definitions for splash, butt tears, flute crack, star crack, burst, mold slag, gassy, dendritic, and refilled crack, among others.

 

[mrfailure]

As EdStainless pointed out, 0.2% and 0.5% are the commonly defined offsets for yield strength. I have never seen 0.6% and wonder if you have a poor copy of the cert that really says 0.5%. Also, note that many specs require yield point, which is different than yield strength (unless the tensile curve does not have an explicit yield point knee below tensile strength).

Aaron Tanzer

http://www.lehightesting.com

 

[Wrenchbender]

What's the question? Why 0.2%?

An offset of 0.2% (strain) is merely customary for practical reasons of measurement, especially with older analog machines using paper traces. (I've read that state of the art testing machines can record very close to zero offset. I've also seen specifications written for a 0.01% in an questionable attempt to chase down the real knee in the curve.) References: Hertzberg, 'Deformation and Fracture Mechanics of Engr Mat'ls', and Faires - 'Design of Machine Elements'

 

[Tmoose]

Yeah, I figured crackles was a translation typo. On other projects from China the NDE reports have refered to crackles. The 1978 Honda CR-250 owner's manual included in the pre-race preparation to inspect the exhaust pipe for "crackers."

Attached is a screen shot of the badly scanned spec we received showing fairly clearly 0.6%, FWIW.

I am comfortable simply using the 0.2% because "that's what we always do."

I was just looking for background on the 0.6%


thanks

Dan T

 

[redpicker]

There probably some confusion between the offset method of determiing yield and the Extension Under Load (EUL) method. See ASTM E370 or E8 for a complete description.

For the offset method, 0.2% percent offset is almost always used. I have seen some other offsets used (0.02%, for example) but this has almost always been in research environments.

For pipe, it is common to use the EUL method. For minimum yield strengths in the 100-130 range, it is common to use a 0.6% extension to determine yield (different values are used for different yeilds, which is obvious once you understand the method). This is a "pipe thing" and it dates back to the days before accuarte extensometers and chart recorders were widely available and pipe mills would just use the EUL method to determine yeild. THere is a small difference bewteen the two methods, about 5% in these cases. That is normal and to be expected.

It's not a typo.

rp

 

[redpicker]

OK, there are some typos in my post above.

That should be "ASTM A370" not "ASTM E370"

It also should be "For minimum yield strengths in the 100-130 KSI range..." instead of "...the 100-130 range...".

Sorry about that.

rp (just call me "TYPO KNIG")

 

[TVP]

Since yield strength is indicated as Re, elongation as A, etc, the applicable standard is EN 10002-1, which is the European equivalent to ASTM E8 or ASTM A370. The 0.6% yield strength is technically called Proof Strength, total extension in 10002-1, and is denoted by the symbol R[sub]t0.6[/sub]. It is equivalent to the EUL method as mentioned by redpicker.