MIL-PRF-32516
APPENDIX C
TEMPERATURE/VIBRATION STIMULATION
C.1 SCOPE
C.1.1 Scope. This appendix deals with ways to isolate faults related to a combination of
operating temperature and vibration. This appendix is not a mandatory part of the specification.
The information contained herein is for guidance only.
C.2 DETERMINING CAUSES OF INTERMITTENT FAILURES
C.2.1 Introduction. LRU/WRAs are different in their function and operational
environments. As a result, no single test method or procedure can adequately replicate an
intermittent fault occurrence for all LRUs/WRAs. A careful review of the nature of the failure
and the operational conditions under which the failure occurred is required. The following steps
are recommended when by careful analysis it is determined that the failures occur during ground
or flight operating conditions.
C.2.2 Typical failures. Temperature, humidity, vibration, and altitude can combine
synergistically to produce the following failures. Although altitude is included in the following
discussion typically in regards to LRU/WRA operating environment it mainly impacts cooling
and is a function of temperature. Typically Combined Environmental Test facilities do not
include altitude test capability. The following examples are not intended to be comprehensive:
a. Shattering of optical material. (Temperature/Vibration/Altitude)
b. Binding or loosening of moving parts. (Temperature/Vibration)
c. Separation of constituents. (Temperature/Humidity/Vibration/Altitude)
d. Performance degradation in electronic components due to parameter shifts
(Temperature/Humidity)
e. Electronic optical (fogging) or mechanical failures due to rapid water or frost formation.
(Temperature/Humidity).
f. Differential contraction or expansion of dissimilar materials. (Temperature/Altitude)
g. Deformation or fracture of components. (Temperature/Vibration/Altitude)
h. Cracking of surface coatings. (Temperature/Humidity/ Vibration/Altitude)
i. Leakage of sealed compartments. (Temperature/Vibration//Altitude)
j Failure due to inadequate heat dissipation. (Temperature/Vibration /Altitude)
C.2.3 Combined forcing functions. A review should be conducted of technical manuals,
operating manuals and any available information, apply the tailoring process in MIL-STD-810 to
determine where these combined forcing functions of temperature, humidity, vibration, and
altitude are foreseen in the LRU/WRA operational environment Use this method only if the
proper engineering has been performed such that the environmental stresses associated with the
individual methods are encompassed by the combined test. If appropriate, tailor storage thermal
environments into the combined environmental cycle; or, perform them as separate tests, using
the individual test methods. Use the following to aid in selecting this method and placing it in
sequence with other methods.
C.2.3.1 Unknown operational limits. Where the temperature/vibration/humidity/altitude
operational limits are unknown, MIL-STD-810, Test Method 520 should be used to tailor the
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