MIL-DTL-24487B (SH)
and measuring the slope of the decaying free vibration. Signal conditioning is desirable in this case as well, and
may be accomplished by translation ("zoom") analysis if the limiting decay criteria is met.
4.5.8.2.3.5 Testing. Each test bar shall be suspended edgewise from two lightweight nylon or cotton cords
at least 24 inches (61 cm) long. The bar may be suspended edgewise or flat, as appropriate for the type of vibration
exciter being used. The suspension cords shall be attached to the bar at the appropriate nodal points of the first
flexural mode of vibration (approximately 5.83 inches (14.8 cm) from each end of the 26 inch (66 cm) bar for
Class 1 damping treatment; approximately 6.50 inches (16.5 cm) from each end of the 29 inch (73.7 cm) bar for
Class 2 treatment). Alternatively, each test bar may be suspended vertically from one end of the bar using a single
cord. For vertically suspended bars, a hole approximately 3/8-inch in diameter and located nominally one inch from
the end of the bar may be drilled through the bar and the damping material. The free bar shall be excited at each of
the odd-numbered lengthwise flexural modes of the bar as required in Tables II and III. Care shall be exercised to
identify the modes excited and to avoid torsional, longitudinal, and combined modes. Care shall also be taken to
prevent overloading of any part of the exciting and sensing circuits to eliminate spurious results. It is very
important that the alignment of the vibration exciter be such that the direction of excitation is normal to the face of
the test bar to which the vibration exciter is attached. Of primary concern is the need to eliminate the effect of the
exciter on the test specimen during the time of the decaying free vibration. After connecting the instrumentation but
prior to measuring the damping properties, the resonant frequency response of the test specimen shall be measured.
In addition to determining the modal frequencies, this process is used in determining misalignment and overload
problems in the exciter and measurement systems.
4.5.8.3 Calculation. The percents of critical damping at each mode found for the three bare bars at 50 °F
(10 °C) shall be averaged. Likewise, the percents of critical damping at each mode found for the three coated bars
shall be averaged. The corrected percents of critical damping for comparison with the requirements in Tables II and
III shall be calculated using the following equation:
Percent of critical damping (corrected) = Dc - D
where:
Dc is the averaged damping of the coated bars at the specified mode at 50 °F (10 °C).
D is the averaged damping of the bare bars at the specified mode at 50 °F (10 °C).
4.5.9 Toxicity. The vibration damping tiles shall be evaluated by the Navy Environmental Health Center
(NAVENVIRHLTHCEN) using the administrative Health Hazard Assessment (HHA). A flowchart for this process
can be found as enclosure (1) of BUMEDINST 6270.8. The HHA is a review of the vibration damping tiles based
on information submitted by the manufacturer, to assess health hazards associated with the handling, application,
use and removal of the product. Sufficient data to permit a HHA of the product shall be provided by the
manufacturer/distributor to the NAVENVIRHLTHCEN. To obtain current technical information requirements
specified by the NAVENVIRHLTHCEN, see 6.5.
4.5.10 Off-gassing. The vibration damping tiles shall be tested in accordance with the Nuclear Powered
Submarine Atmosphere Control Manual, NAVSEA Technical Manual S9510-AB-ATM-010 Rev. 2, by a
Government approved testing facility. The results shall be submitted to the Government for evaluation and approval
for use (see 3.2.2 and 6.6).
5. PACKAGING
5.1 Packaging. For acquisition purposes, the packaging requirements shall be as specified in the contract
or order (see 6.2). When packaging of materiel is to be performed by DoD or in-house contractor personnel, these
personnel need to contact the responsible packaging activity to ascertain packaging requirements. Packaging
requirements are maintained by the Inventory Control Point's packaging activities within the Military Service or
Defense Agency, or within the military service's system commands. Packaging data retrieval is available from the
managing Military Department's or Defense Agency's automated packaging files, CD-ROM products, or by
contacting the responsible packaging activity.
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