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Conditions that Give Rise to the Need for
Environmental Simulation Testing
by Sheldon Levine


Introduction

It is widely understood that environmental simulation testing is
necessary to certify that equipment is capable of withstanding
extreme conditions such as found in the desert, in the tropics,
aboard marine vessels and aircraft, exposure to solar radiation,
high humidity, and extreme hot and cold temperatures.

There exist a great number of commercial and military specifications
which cover a wide range of environmental test requirements. However
what is often not known or well understood are the actual
environmental conditions that give rise to the need for such
testing. The following paragraphs present a discussion of some of
these environments.

Salt Atmosphere

The oceans are the world’s primary source of salt. The salt
solutions of the oceans range from 3.5 to 3.9 %. Also winds over the
oceans surfaces carry anywhere from 10 to 100 pounds of salt per
cubic mile of air. Salts such as sodium chloride, potassium
chloride, and calcium and magnesium are highly soluble in water and
form strong electrolytes. As a result marine environments are highly
corrosive and readily attack many different materials.

To certify that materials can withstand the marine environment salt
chambers subject equipment, typically to a 5% salt solution with
water temperatures of 95 degrees F.

Sand and Dust

Extreme sand and dust conditions are found in industrial areas,
deserts, and other areas where there has been little or no rainfall.
Sand and dust can be extreme problems during blowing wind conditions
since it can penetrate even sealed equipment as well as internal
portions of aircraft. Blowing sand can be found at elevations as
high as 10,000 feet. Sand and dust chambers can develop wind
velocities of 300 to 1750 ft/min for dust and 3500 to 5000 ft/min
for sand, and can handle various grades of sand such as found in
different parts of the world.

Solar Radiation

Organic and synthetic materials are strongly affected by ultraviolet
and infrared solar radiation. Rubber deteriorates, plastics darken,
polymers lose strength and toughness, and colors fade. The greatest
solar radiation occurs in the tropics, but can occur in temperate
zones under certain conditions. Also solar heat loads can have an
adverse effect on equipment operation. Both full spectrum solar and
heat loads can be simulated in the laboratory.

Humidity

Non-metallic materials absorb some moisture, which cause changes in
electrical properties. High humidity in combination with other
conditions, i.e., salt-air and high temperature, offers significant
problems in corrosion control. Relative humidity of up to 100% and
temperatures exceeding 85 degrees F require measures to prevent
corrosion. Humidity testing is performed by maintaining a relative
humidity of 95% while cycling through various temperatures.

Fungus

Fungi are a class of microorganisms that feed on organic material
such as printed circuit boards, lubricants, and greases. The ideal
growth conditions for fungi are temperatures between 68 and 104
degrees F and relative humidity between 85 and 100%. Fungus
chambers incubate fungi by maintaining a typical temperature
of 86 degrees F and 90-100% relative humidity.

Temperature

Extremes of temperature can affect equipment operation. Also rates
of corrosion, fungus growth, and moisture condensation vary at
different temperatures. Temperature chambers can operate at a range
of –80 to 1200 degrees C (-112 to 2192 F), although the typical
range is –70 to 177 degrees C (-94 to 351 F).

Conclusion

The proper choice of materials and the application of appropriate
protective coatings will ensure that corrosion and degradation will
be held to a minimum. To ensure that the proper materials and
protective coatings have been utilized environmental simulation
testing should be performed.




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