On Thu, 23 Feb 2012 17:48:49 -0500, "Jim Wilkins"
wrote:


"Ned Simmons" wrote in message
.. .
On Thu, 23 Feb 2012 16:29:41 -0500, "Jim Wilkins"
wrote:

That .2% is the amount of non-elastic stretch used to define the
yield
point; it's not the amount of elastic deformation before yield. The
suggestion was to measure *elastic* strain (delta length/length) in
order to determine tension. The change in length before yield will
be
approx = stress/Young's modulus x length, stress equal to
tension/area. Still a small number.

--
Ned Simmons

If Young's Modulus is 30E6 and the load is 30E3, what's the
elongation?

jsw


Depends on the cross sectional area and length of the member. If, for
example, the load is 30E3 lb on 1 in^2 of steel (Y=30E6 lb/in^2):
stress = Force/area = 30E3 lb / in^2
strain = stress/Young's modulus = 30E3 lb/in^2 / 30E6 lb/in^2 = 1E-3
in/in

Over a 10 inch length the change would be 10 in x 1E-3 in/in = .01 in

In other words, strain is a ratio that represents the change in length
(length/length) of a body under strain.

--
Ned Simmons