2.1 Effects of the Environment
This Method induces physical changes in or on non-stationary materiel. Examples of problems that could occur during these tests are as follow:
- a. Distortion or binding of moving parts.
- b. Failure of bonding materials.
- c. Failure of seals.
- d. Failure of materials due to freezing/re-freezing of absorbed, adjacent, or free water.
- e. Changes in characteristics of electrical components.
- f. Electrical flashover/reduced insulation resistance.
- g. Fogging of optical systems during freeze-thaw transitions.
- h. Inability to function correctly due to ice adhesion and interference or blockage of moving parts.
2.2 Test Procedures
When a freeze/thaw test is thought necessary, the three procedures included in this Method are suitable for most materiel:
MIL-STD-810H
METHOD 524.1
2.2.1 Procedure I – Diurnal Cycling Effects
To simulate the effects of diurnal cycling on materiel exposed to temperatures varying slightly above and below the freeze point that is typical of daytime warming and freezing at night when deposits of ice or condensation, or high relative humidity exist. For Procedure I to be effective, frost must form on the test item surfaces during the temperature increase through the freeze point, and then melt just prior to re-freezing.
2.2.2 Procedure II – Fogging
For materiel transported directly from a cold to a warm environment such as from an unheated aircraft, missile or rocket, to a warm ground area, or from a cold environment to a warm enclosure, and resulting in free water or fogging.
NOTE: Tests for fogging are only appropriate for materiel designed to not fog or that has built-in de-fogging capabilities.
2.2.3 Procedure III – Rapid Temperature Change
For materiel that is to be moved from a warm environment to a cold environment (freeze) and then back to the warm environment, inducing condensation (free water).
2.3 Determine Test Levels and Conditions
Specify the most significant parameters for this Method such as temperature, moisture level/form, test item configuration (operational or storage), and the number of freeze/thaw cycles.
2.3.1 Test Item Configuration
Perform the test using all the configurations in which the materiel may be placed during its life cycle. As a minimum, consider the following configurations:
- a. In a shipping/storage container or transit case.
- b. Protected or not protected.
- c. In its operational configuration.
- d. Modified with kits for special applications.
2.3.2 Temperature Range
Use temperatures within the storage or operational range of the test item. Normally, the temperature cycle ranges between +5 °C and -10 °C (41 °F and 14 °F) for diurnal cycling effects, and -10 °C (14 °F) to standard ambient (Part One, paragraph 5.1), but these vary as required to achieve the desired effects.
2.3.3 Moisture
Use water needed to create the test moisture from local (clean) water sources. Apply the moisture as a water vapor or as free water (spray).
2.3.4 Number of Cycles
A cycle is a change from one thermal-moisture condition to another and back to the original condition. Unless otherwise specified in the test procedure(s), hold the test item at each condition for a minimum of one hour following test item temperature stabilization. Unless otherwise justified by the materiel's life cycle profile, apply the following minimum number of cycles:
- a. Diurnal cycling effects (daily freeze-thaw): Minimum of twenty (see Part Three, paragraph 5.9a, and paragraph 6.1, reference c).
- b. Cold-to-warm transfer (for free water or possible fogging): Three.
- c. Warm-cold-warm (for freezing and melting, rapid temperature change): Three.
MIL-STD-810H
METHOD 524.1