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Carl Carl is offline
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Default Get -40C in my fillet weld tensile break tests

On 2/5/21 3:28 AM, Richard Smith wrote:
Joe Gwinn writes:

On Thu, 04 Feb 2021 11:43:58 +0000, Richard Smith
wrote:

Ideas to get a controlled temperature of around -40C (also -40F) in a
test sample?

"Robustly" by physics:
100C - boiling water
0C - ice
-17C - brine-ice slurry (?)
??? -40C ???
-80C - "cardice" - solid CO2
-196C - liquid nitrogen

Reason is, found a way to tensile-test fillet welds, and so far always
seeing breaking strength come out at around 560MPa, when you do the
maths relating breaking force to the fracture area.

The 355MPa yield of the Rectangular Hollow Sections (RHS) isn't seen -
and I know they have exactly that yield stress from beam bending
measurements.

Here's the tests - "Alladin's Cave" of misdemeanours and skulduggery ?
;-)

http://www.weldsmith.co.uk/tech/struct/struct.html
"Steel Structural Performance index-page"

Various tests.

Specifically the fillet weld tensile tests

http://www.weldsmith.co.uk/tech/struct/201124_fwbeamt/201124_fwbeamt.html
"Fillet welds tensile tested in beam test"

http://www.weldsmith.co.uk/tech/struct/210122_fwtest_rig/210122_fwtest_testrig.html
"Tensile-test rig for beam-configuration fillet-weld samples"

Movie of - 10 seconds - shared on "Dropbox"
https://www.dropbox.com/s/esgwfk5jenhm024/210122_fwtr.mp4?dl=0

Yup, I know that as a PhD level scientist I have to work as a welder
because everyone already ensconced in "office engineering" jobs
manicured in their white shirts sees me as a "Dennis Hopper like"
(think eg. "Blue Velvet" (1986) film) character of the science and
engineering world ;-)
If you keep the office door closed to all but your own manicured kind,
you can keep reality out. Who can blame them if no-one comes and
hurls them out into the cold hard world their scheme avoids? :-)

It would be helpful to see whether that "no yield event - straight to
local fracture at high(er) stress" is associated with a low
temperature brittleness charactistic.

I could "dam-off" the RHS close to the weld and at the far end, and
fill it with a cooling fluid.
Ice-brine looks good for -17C.

Throw a blanked over the entire sample for a while for all parts of
the sample to be at that temperature, then slide in the hydraulic
cylinder and "pump it up" and see what the temperature causes or does
not cause.

What about for -40C
???


Propane boils at -42 C at atmospheric pressure.

Joe Gwinn


Thanks for suggestion. Well rooted in science.
I fear that as the sample gets colder with propane evaporation, we
could get a hair-trim if the evaporated gas ignites.

The sample halves hurl around on sample weld breaking, so putting on a
"vent tube" with the propane burning at the outlet - a "flare" -
doesn't seem a viable solution.

It might be that I have to do something with "cardice" - solid CO2.
Throw-in bits until reaches -40C.

Or cool to lower temperature and pump the cylinder when weld area has is
showing -40C by thermocouple.

Thanks for suggestions.

I just looked online and find
https://en.wikipedia.org/wiki/Brine
that lowest melting point is -21.1C

Something you learn about experimenting - while you do make sure
everything holds together as it should, you don't look for the n-th
degree of accuracy of physical conditions in the proof-of-concept
tries.

To think in planning that a particular exact temperature is important
is the error of thinking that if you specify something enough, "God"
has to conform. Not going to happen. Get a pretty cold temperature
and observe what is there to observe.


There are lots of other things besides sodium chloride to make "salt"
baths from :-). See https://en.wikipedia.org/wiki/List_of_cooling_baths
for one list, and look at reference 2 and the reference pdf in ref 2
(https://www.larkinweb.co.uk/science/...ng%20baths.pdf) for
a bit more info. I'd try calcium chloride hexahydrate/water either at
the ratio for -41C or a bit stronger since they say it is difficult to
reach the listed temps. You could also precool your metal with dry ice
and even add some dry ice to the salt bath while it is cooling down, or
put the salt bath in a small tub in a larger tub with dry ice packed
around it. I'd make the starting ice either from distilled water (cheap
at grocery stores) or reverse osmosis water if you have a home system
already. If having the metal dripping with wet calcium chloride is a
problem during your test put the piece in a ziploc bag. Partially seal
the bag so about an inch at one side is still open then slowly submerge
the bag in plain water while holding that corner out of the water. The
air will be forced out so you get good contact between bag and metal for
good heat transfer. Finish sealing the bag when as much of the air as
possible is removed. Just pretend it is a steak you are about to cook
sous vide :-).

--
Regards,
Carl