Impact test converison
Chris North
convert Charpy impact test requirements from J/cm2 to something normal
(like Ft-Lbs, or even Joules?).
I have a spec that calls for an average of "43 J/cm2 with KV-specimen
10 x 7,5"
The way I understand it, the J/cm2 value is obtained by taking the
energy value (in Joules) and dividing by the area under the notch
(which would be .8 cm^2 for a standard 10 x 10 CVN specimen, right?).
So, if a specification called for a minimum average of 43 J/cm2 and I
broke 3 10 x 10 specimens, I would have to acheive an average of 34.4
Joules (43*0.8cm^2) or 25.4 Ft-Lbs. Is this correct?
Using this notation for the impact requirement would make the specimen
size irrelevant, correct? That is, if a spec called for 43 J/cm2 on a
10 x 7.5 specimen, that would mean a minimum of 25.8 Joules
(43*0.6cm^2), right?
Or am I just making this too complicated? Could this all mean that
they want 43J impact strength on a 10 X 7.5 specimen and they are
adding the "/cm2" part because they don't know what they are doing?
Thanks for any help
Chris N
JFMACR
Go to this site and look under energy
http://www.onlineconversion.com/energy.htm
Jim MacRae
PSI, Inc
Birmingham, AL
Chris North
it doesn't list J/cm^2 as a convertable uint.
Chris N
jfm...@aol.com (JFMACR) wrote in message news:<20020729230911...@mb-ma.aol.com>...
JFMACR
Chris North
10 x 7,5". What do I convert this to?
jfm...@aol.com (JFMACR) wrote in message news:<20020731072648...@mb-ba.aol.com>...
Ian Matheson
you in university... it sounds like everybody is confused in this NG.
There are TWO types of Charpy impact test, the Charpy V and the Charpy
U, the former being the most popular. They get their names from the
shape of the notch in the specimen. Now originally the Charpy V test
results were reported as being in kgfm/cm^2 or kpm/cm^2 while the
Charpy V test results were reported as being in kgfm or kpm. (1 kgfm
= 1 kpm and multipy by g to convert to J). (Note I'm South African
and we tend to side with the Europeans in the units debate)
Here's where the fun starts, ISO then came along decided to change the
units for the Charpy V test to J and also the units for the Charpy U
test to J as well.
Now I think you can see that this planted the seeds of confusion,
because now when people see the same units, they think that there is
only one Charpy test, not two and try to compare apples with pears.
Thelning's "Steel and its heat treatment" 2nd Ed. has the chart of
Charpy V vs Charpy U.
Cheers
Ian
chr...@wt.net (Chris North) wrote in message news:<256592b5.02073...@posting.google.com>...
David
"Ian Matheson" <ian_ma...@hotmail.com> escribió en el mensaje
news:a34e74b5.02080...@posting.google.com...
> Uh oh, welcome to the world of impact testing that they never taught
> you in university... it sounds like everybody is confused in this NG.
>
> There are TWO types of Charpy impact test, the Charpy V and the Charpy
> U, the former being the most popular. They get their names from the
> shape of the notch in the specimen. Now originally the Charpy V test
> results were reported as being in kgfm/cm^2 or kpm/cm^2 while the
> Charpy V test results were reported as being in kgfm or kpm. (1 kgfm
> = 1 kpm and multipy by g to convert to J). (Note I'm South African
> and we tend to side with the Europeans in the units debate)
> Here's where the fun starts, ISO then came along decided to change the
> units for the Charpy V test to J and also the units for the Charpy U
> test to J as well.
too old, just looking up at university books); It is the same as Charpy V
with the addition of a 1mm fatigue crack (GOST 9454-60 says my book), you
get the result in kgf (Guess it´s the same as kgfm) to be divided by 0.8
cm^2 (transversal section of normalized ¿"test units"? (Sorry, language
problems here.....).
Fred Fletcher
J/cm^2 is that the thickness of the Charpy specimen becomes irrelevant.
This is important for lighter gauge plates--lighter than 10 mm, that is.
Such an approach is a vast improvement over specifying different energy
values for different plate thicknesses. The people who put this together
definitely knew what they were doing!
Fred Fletcher
Michael Dahms
>
> Your analysis is correct. The reason for specifying absorbed energy in
> J/cm^2 is that the thickness of the Charpy specimen becomes irrelevant
Your statement is incorrect. The fracture energy of specimen with
different crosssections is _not_ proportional to the cross section.
Michael Dahms
Chris North
That is what I was thinking. I seem to recall that early in the
development of the Charpy test, they tired to take this approach, but
discovered that there was a lot more to the fracture energy of a
Charpy specimen than just the cross sectional area (or the area of
fracture). Thus, the reason for standardizing on the specimen size
(and staying with standard sub-sized specimens when full-sized
specimens were not possible).
The original specification requirement came from an eastern Europe
concern, and I am not familar with their common practices. From
surfing steel suppier sites in former USSR countries, it seems common
to use KCU (as well as KCV) testing and express the requirements in
terms of J/cm2. I was hoping that someone with experience with their
practices could explain what they mean.
Chris N
Michael Dahms
>
> The original specification requirement came from an eastern Europe
> concern, and I am not familar with their common practices.
Ask for a copy of their impact-testing-standard.
You should then carry out impact tests according to their standard.
That's the only proper way.
Michael Dahms