From shock response spectrum to temporal moments and vice-versa Page: 3 of 7
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Proceedings of the 21' SEM International Modal Analysis Conference (IMAC-XXI).
Kissimmee, Florida, February 3-6, 2003.
The threaded assembly was instrumented with
thirty-three strain gages attached to the inside surface
of the titanium mount. The strain gages provided data
on the localized propagation of the shock around the
circumference of the mount. The strain gages had an
active length of 0.8 mm to obtain localized effects. One
of the strain gages was found to be faulty during the
pre-test check of the sensors.
In addition, six accelerometers (Endevco 7270A-
200k, 1 mV/g) were used to instrument the acceleration
response of the mass simulators. They were located on
either end of both payload mass simulators. Four were
oriented laterally in the direction of the delivered
impulse and two were oriented along the axis of the
structure, see Figure 3.
Figure 3.Location of Accelerometers.
The conditioned strain signals had a frequency
response of 100 kHz and the accelerometer signals
had a frequency response of 500 kHz. This study is
restricted to the acceleration responses collected at
sensors 5 and 6 because they were found to be the
most important signals for the purpose of the analysis.
2.3 Explosive Source
Extensive research was performed to determine
the impulse-loading configuration. Design requirements
were that the pressure peak at the surface of the
threaded assembly be less than 5 kbar with an impulse
between 2 and 4 ktaps.
The design requirements were met by interfacing
the sheet explosive with a buffer layer. A neoprene
buffer was chosen such that the resulting pressures fit
within the design requirements. The low-level impulse
was achieved by cutting the sheet into strips and
spacing them out over the target area. Figure 4 shows
that the pressure load applied directly under a strip is
very similar to the load applied between two strips,
therefore, verifying our computational load model.
Approved for unlimited, public release on October ??, 2002.
Figure 4 also shows that the pressure history is a short-
duration event (1.8 micro-second), therefore, providing
a good realization of an impulse excitation.
Figure 4. Measured pressure history.
2.4 Test Matrix
A suite of four tests was conducted in July 1999.
Additional testing will be conducted in the year 2003.
Two experimental factors were studied in this test suite,
the manufacturing tolerance for the aluminum shells
and an assembly tolerance.
Two sizes of Al shells were manufactured, one
with nominal clearances (the "loose" set) and one with
smaller than nominal clearances (the "tight" set). The
assembly tolerance relates to how much radial
clearance is allowed between the lower shell and the
mount directly behind the location of the explosive
charge. Figure 5 illustrates the assembly tolerance or
"gap" that can be opened or closed when the
components are assembled.
L * Upper
Figure 5. Definition of the assembly tolerance.
The combinations of these factors for each test
are shown in Table 1. Tests 1 and 2 were repeated
tests intended to give a bound for the test-to-test
repeatability. However, the structure for test 1 was
assembled at Los Alamos and shipped for testing, while
5.0 Experiment 5 6/25/99
1/-inch neoprene buffer
4.0 0.27-inch spacing between strips
-- Under n strip
3.0 - Between a strip
-1. , ?^ , , , i ,
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Hemez, F. M. (François M.) & Doebling, S. W. (Scott W.). From shock response spectrum to temporal moments and vice-versa, article, January 1, 2002; United States. (https://digital.library.unt.edu/ark:/67531/metadc930956/m1/3/: accessed April 24, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.