MIL-DTL-19379C(SH)
4.4.2.3 Fatigue-drift test. The test apparatus shall be capable of providing cyclical vibration to the test fixture.
Refer to figure 3. All mount height measurements shall be to the nearest 0.001 inch. The mount shall be secured in
a test fixture and axially loaded in compression with a mass to its upper-rated load. One hour after application of the
mass, mount height shall be measured. The fixture shall then be vibrated at the natural frequency of the mount-mass
system in the axial direction for at least 500,000 cycles. The amplitude of the excitation force shall ensure the
mount is deflected 0.05 inch each side of the equilibrium position (0.10 inch double amplitude). The vibration tests
shall be conducted at regular and equal time intervals for 4 consecutive days. The mount shall remain loaded for the
entire fatigue-drift test, including the time periods between vibration intervals. Mount height shall be measured at
the end and beginning of each vibration test run. A final mount height measurement shall be made 96 hours after
initial static loading. Mount drift to determine compliance with 3.5.4 shall be the difference in the height
measurements taken 1 hour after loading and 96 hours after loading. The test shall be conducted at an ambient
temperature of 80±5 °F. NOTE: It is usually convenient to measure the amount of drift from an arbitrary datum
from which the change in mount height can be determined.
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