Testing Disciplines
Fungus
| The purpose of the fungus test is to assess if the test item will support fungal growth or how the fungal growth may affect performance or use of the test item. | |
| Fungal growth impairs the functioning of or use of equipment by changing its physical properties. The detrimental effects of fungal growth are summarized as follows: | |
| Direct Attack | |
| Nonresistant materials are susceptible to direct attack as the fungi break the material down and use it as food. This results in deterioration affecting the physical properties of the material. | |
| Indirect Attack | |
| Damage to fungus resistant materials results from indirect attack when: | |
| Fungal growth on surface deposits of dust, grease, perspiration, and other contaminants (which find their way onto equipment during manufacture or accumulate during service) causes damage to the underlying material even though that material may be resistant to direct attack. | |
| Metabolic waste products (i.e., organic acids) excreted by fungi can cause corrosion of metals, etching of glass, or staining or degrading of plastics and other materials. | |
| The products of fungal growth or adjacent materials which are susceptible to direct attack come in contact with the resistant materials. | |
| Physical Interference | |
| Electrical or electronic systems - Damage to electrical or electronic systems may result from either direct or indirect attack. Fungal growth can form undesirable electrical conducting paths across insulation materials or may adversely affect the electrical characteristics of critically adjusted electronic circuits. | |
| Optical systems - Damage to optical systems results primarily from indirect attack. The fungal growth can adversely affect light transmission through the optical system, block delicate moving parts and change non-wetting surfaces to wetting surfaces with resulting loss in performance. | |
| Health and aesthetic factors - Fungal growth on equipment can cause physiological problems (e.g. allergies) or be so aesthetically unpleasant that the users will be reluctant to use the equipment. | |
| Test Objective | |
| The primary objectives of the fungus test are to determine: | |
 If
fungi will grow on the test item |
|
| How
rapidly fungus will grow on the test item |
|
| How
any fungal growth affects the test item. |
|
| To
what extent the fungus will affect the mission of the
test item. |
|
| If
the test item can be stored effectively in a field
environment |
|
| If
the test item is safe for use following fungal growth. |
|
| If
there are simple reversal processes, e.g. Wiping off
fungal growth. |
|
| Test Duration | |
| Twenty-eight days is the minimum test period to allow for fungal germination, breakdown of carbon molecules, and degradation of material. | |
| Since indirect effects and physical interference are not likely to occur in the relatively short time frame of the fungus test, extension of the test period to 84 days should be considered if a greater degree of certainty (less risk) is required in determining the existence or effect of fungal growth. | |
| Test Item Configuration | |
| The item configuration is an important factor. Even though equipment is to be protected by a container, the container could leak and entrap moisture. As a minimum, the following test configurations should be considered: | |
| In
its normal shipping/storage container or transit case. |
|
| Under
realistic storage or use conditions. |
|
| With
restraints (such as with openings that are normally
covered). |
|
| Choice of Test Fungi | |
| Various species of test fungi are selected dependent on the test specification. These organisms are selected because of their ability to degrade materials, their worldwide distribution, and their stability. | |
| Additional species of fungi may be added to those required when using any test method. If additional Fungi are used, their selection is based on prior knowledge of specific material deterioration. | |
| Typical Test Specifications | |
| MIL-STD-454 |
MIL-T-18404 |
| MIL-STD-810 |
ASTM
G21 |
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