On Fri, 24 Feb 2012 12:29:22 -0500, "Jim Wilkins"
wrote:


"Ned Simmons" wrote in message
.. .
On Thu, 23 Feb 2012 20:11:33 -0500, "Jim Wilkins"
wrote:

I agree with your conclusion, but the .2% number you used to get
there
has nothing to do with elastic deformation, and it's only a
coincidence that our numbers are close. I could just as easily have
used .1 in^2 as the area in my example, and the resulting strain
would
be 10mm per meter.

I suspect the practical limitations of tensile testing machines 100
years ago is why the transition from elastic to plastic was
designated
at .2% elongation. In other words, that's what could be reliably
detected.
Ned Simmons

I should have written 30E3 PSI, not total stress. 300KSI material is
beyond my machining and heat-treating ability so its superior
elongation doesn't help for homebrew load cells.

300ksi is close to the ultimate tensile of the highest strength steel
wire used in cable, so clearly you wouldn't tension it anywhere near
that level. I was just trying to clarify the distinction between the
..2% elongation (that's used to mark the elastic/plastic boundary) and
the elastic elongation that occurs between 0 PSI and yield.


I operated one of those old Tinius Olsen tensile strength machines in
a test lab and agree with you. It was kind of tricky to get good
repeatable results from it.

jsw


I've never operated one, but can imagine there are lots of variables
that are difficult to control.

--
Ned Simmons