yield strength: permanent deformation or elastic?
richar...@craneaerospace.com
Yield Strength is the maximum load at which a material exhibits a
specifed deformation (such as 0.2% or 0.5%).
Is that _permanent_ or _elastic_ deformation?
I would usually associate "yield" with "whoops, I bent it", but I see
"deformation" used to describe elastic changes in shape as well as
irrecoverable stretchs, bends and dents.
I see that the "yield point" is the point in the stress-strain diagram
where elastic behavior has been exceeded and the metal won't recover,
but the text makes clear the two terms serve different purposes.
I'm wondering whether it means "force to temporarily flex it .2%", or
"force to permanenetly bend it .2%".
(A followup question would be: "shouldn't there be different yield
strengths for stretching, bending and denting?" I can see that
geometry matters for such things (and perhaps even more so for
twisting), and that we want 'yield strength' to be a bulk property
independent of shape ... but stretching aint denting ... is it? Am I
stumbling over "tensile" vs."compressive" failure but don't know how
to say it?)
Thnaks to whoever turned me on to this book - at about a penny a page
it's the best entertainment value I've had since ... well, ever!
Rick Corey
Cheap In the Pacific NorthWet
Good soldier
In general the strength of a material is measured, by stretching
(tensile strength), there probably are other tests done but I have
never seen them actually specified and I have seen tables that give a
predicted sheer strength from a tensile strength.
From a tensile strength one can calculate the material's resistance to
other forces (google "Modulus of Elasticity" for more information.
alv...@example.com
> I read in Metallurgy Theory and Practice (Dell K. Allen, c 1969)
> that Yield Strength is the maximum load at which a material
> exhibits a specifed deformation (such as 0.2% or 0.5%).
> Is that _permanent_ or _elastic_ deformation?
Permanant and measurable. :)
> I would usually associate "yield" with "whoops, I bent it", but
> I see "deformation" used to describe elastic changes in shape as
> well as irrecoverable stretchs, bends and dents.
If I remember right elasitic has to do with the atomic attraction
and stretch of the iron atoms. All steels are about the same there
and is similar to the notion of "stiffness".
> I see that the "yield point" is the point in the stress-strain
> diagram where elastic behavior has been exceeded and the metal
> won't recover, but the text makes clear the two terms serve
> different purposes.
Yes. :)
And I've used "elastic" wrong here too, on purpose.
Because "elastic" is very discriptive IMO.
> I'm wondering whether it means "force to temporarily flex it .2%",
> or "force to permanenetly bend it .2%".
Permanently deformed as in "plastic deformation" as in Super Putty.
> (A followup question would be: "shouldn't there be different yield
> strengths for stretching, bending and denting?"
Yes there are. I can't recite them off hand tho. :/
"Resistance to being dented tables ;)"
aka: Hardness Convertion Tables...
Have a column included that shows the approximate strength of the
material at various hardnesses or "resistance to being dented
ratings ;)".
Table 2-1 Page 29 :)
> I can see that geometry matters for such things (and perhaps even
> more so for twisting), and that we want 'yield strength' to be a
> bulk property independent of shape ... but stretching aint denting
> ... is it?
Well no, but they are related, all this stuff overlaps in places
since none of the properties can be completely independent from
all the others.
> Am I stumbling over "tensile" vs."compressive" failure
> but don't know how to say it?)
Not really but sort of... but you're doing real good. :)
If I understood it better (at this time I'm pretty rusty) I would
try to help here now. If you're still interested I'll get my old
stuff out and go over it and come up to speed. At his point you are
about to run over me from behind! ;)
> Thnaks to whoever turned me on to this book - at about a penny a
> page it's the best entertainment value I've had since ... well,
> ever!
> Rick Corey
> Cheap In the Pacific NorthWet
Cool! :)
At least it's cheap. ;)
Alvin squeaks when he walks in AZ
richar...@craneaerospace.com
I never knew what a complex, schizophrenic, multi-personality material
iron was, once you got a little carbon into it. Does it change phase
when a nearby mouse passes gas?
I hit the table that tries to show every possible phase transition on
one diagram.
My head exploded and is just now re-assembling itself.
I'm thinking I need to find two or three more books that explain that
one table -
a little piece at a time, please!
Rick Corey
Cheap in the Pacific Northwet