testing tech
D6484), adopted directly from a Boeing
internal document. The Boeing specimen was 12 inches long. When the ASTM
standard was written, the ���soft��� metric conversion was 300 mm. But this is
4.8-mm shorter than the original Boeing
specimen and, therefore, the English
version of the ASTM D6484 test ���xture
is not suitable for use. This is because
the Boeing test provides 0.2 inch/5.1 mm
of clearance between the two halves of
the ���xture to allow for elastic compression of the specimen before failure at the
hole. There will be insuf���cient clearance
(only 0.3 mm) if the shorter S.I. units
specimen is used in the U.S. Customary
units ���xture. The ���xture will bottom out
before specimen failure is achieved. Dozens of similar examples could be listed.
The ASTM soft conversions issue
aside, other standards organizations
also introduced minor changes that introduce similar complications. The result is that many testing laboratories are
forced to have two (or more) test ���xtures
available to perform the same test, depending on the standard they are obligated to follow for a particular customer.
It���s possible that all of this could be
justi���ed if the differences mattered. But they
don't. For example, let us follow-up with
the Open-Hole Compression test method. At essentially the same time that
Boeing developed its test con���guration
(in the mid-1980s), Northrop Corp. (West
Falls Church, Va.) developed its own test
method. Although Northrop���s method
also required a 0.25-inch diameter hole,
its specimen is only 1-inch wide rather
than 1.5-inches wide and, more importantly, only 3-inches long. It was later
clearly shown that the Northrop test
method produced the same test results
Learn More
@
www.compositesworld.com
Read this article online at
http://short.compositesworld.com/COb24rlR.
Read Dr. Adams��� previous columns on the
subject of composites testing standards:
���Why standardization?��� in HPC May 2007
(p. 11) or visit http://short.compositesworld.
com/9pOAXI1r.
���Test method globalization and harmonization���
in HPC July 2007 (p. 9) or visit http://short.
compositesworld.com/vs8StqBt.
as the Boeing method, even though the
specimen was 9-inches/229-mm shorter.
It becomes obvious that the small (4.8
mm) difference between the U.S. Customary units specimen length and the
S.I. units length for the Boeing specimen
itself is of little technical importance.
ASTM could single-handedly make
a major contribution to solving these
problems by simply converting all of
their standards to S.I. units only and
abandoning all English units. ASTM
could even keep the existing soft conversions. However, the U.S. aerospace industry is strongly opposed to converting
to S.I. units, and because it has a strong
in���uence on ASTM, the latter is unlikely
to make the change.
This opens the possibility that, in this
age of growing globalization, the remainder of the world will leave the U.S. and its
U.S. Customary units behind, isolated
from the global mainstream. Perhaps, in
fact, this is already happening.
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Jan. 29-31, Booth # 1245
january 2013
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