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If the elastic and plastic properties
of a material or product are evaluated for quality control,
specification conformance, or engineering design, you must
obtain precise and critical data. Much of this data can
be most conveniently obtained from your universal testing
machine through the use of electronic strain instrumentation
and related accessories.
Tinius Olsen has pioneered the development
of such equipment since the first autographic recorder was
introduced in 1890. Our revolutionary application of electronics
to testing equipment enabled us to achieve a breakthrough
development in the early 1930's with the first electronic
stress-strain recorder and instrumentation. And that development,
in turn, has spawned today's complete line of strain measuring
instrumentation.
However, in all cases it is most
important that the proper instrument for the job is chosen.
Primary considerations in this selection process include
the calibrated range(s) required to obtain the classification
(accuracy) required by the applicable specifications, the
gage length, a suitable clamping arrangement based on the
size and composition of the specimen, and a sufficient measuring
range.
For example, when determining the
modulus or yield strength of metals and other high modulus
materials, an extensometer that provides a calibrated range
of 2% or less is recommended to assure ample resolution
and accuracy.
If additional properties such as
Yield Point Elongation, Uniform Elongation, Total Elongation,
Strain Hardening Exponent (n) or Plastic Strain Ratio (r)
are also required, the chosen extensometer must also have
additional calibrated ranges covering the associated elongation.
A typical complete stress-strain curve from a metallic specimen
using a high resolution 2% strain range for the modulus
and yield portion and switching to a 50% range for the remainder
of the test is shown below.
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