MIL-DTL-25427B
4.8.12.2 Fatigue.
(a) The connected couplings shall be vibrated for 25 hours in a test setup similar to that
shown in figure 3 at the highest resonant frequency for the direction perpendicular to the axis of
the coupling. If a resonant frequency does not exist for a direction perpendicular to the axis of
the coupling, the coupling shall be vibrated at 55 cycles per second and a double amplitude of
0.060 inch.
(b) The connected couplings shall be vibrated an additional 25 hours in a test setup
similar to that of figure 3, except that the direction of the applied amplitude shall be parallel to
that of the coupling axis. The frequency of the vibration shall be at the highest resonance for the
direction parallel to the coupling axis. If a resonant frequency does not exist for a direction
parallel to the axis of the coupling, the coupling shall be vibrated at 55 cycles per second and a
double amplitude of 0.060 inch.
(c) The first 25 percent of each of the above tests shall be conducted at a temperature of
275° ± 5 °F. The remaining 75 percent shall be at 225° ± 5 °F.
(d) Throughout each of these fatigue tests the coupling shall be subjected to pressure
impulses having a frequency of 30 ± 5 cycles per minute. The impulse test machine shall
produce dynamic pressure impulses in the coupling of the magnitude indicated by the graph
shown on figure 5. An oscilloscope photograph of the nature of the impulse shall be recorded.
(e) At the conclusion of the fatigue tests, the coupling shall successfully pass the leakage
at high pressure and leakage at low pressure tests (see 4.8.5.1 and 4.8.5.2, respectively).
4.8.13 Impulse (5000 psi coupling). The mated coupling and disconnected coupling
halves installed with caps and plugs shall be subjected to impulse test in accordance with the
general requirements of SAE-AS603. Test conditions shall conform to table IX and test setup
conforming to figure 3 and hose band radii conforming to table VIII. The impulse test machine
shall produce dynamic pressure impulses, in the coupling, of the magnitude indicated by the
graph shown on figure 5. An oscilloscope photograph of the nature of the impulse shall be
included in the test report.
4.8.14 Vibration (5000 psi). The connected coupling shall be vibration tested in
accordance with MIL-STD-810, test method 514.6, test procedure I for jet aircraft with an
exception of the following specified herein. The couplings shall be pressurized to 15 psig and
shall be mounted in a similar resonant-free test fixture as shown on figure 3. Figure 4 indicates
vibration exposure experienced on the product mounted on jet aircraft. Tolerances of the
vibration characteristics shall be as follow:
Amplitude
+ 10%
+ 2%
Frequency
Acceleration
+ 10%
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