Aerospace & Defense Technology - December 2021 - 12

Test & Measurement
The Rugged Environment Challenge
EMI materials can include everything
from microwave absorbers to conductive
elastomers to metals. These solutions
operate in a variety of environments
(from saltwater to low-earth
orbit) and, therefore, face an almost
endless list of environmental conditions
that can degrade their performance.
Though the list of environmental
challenges is extensive, there are three
big issues that rise above the rest:
* Corrosion can wreak havoc on materials,
especially in naval applications.
EMI materials that will be exposed to
moisture must be designed to resist
corrosion, and testing must prove that
resilience. Further, galvanic corrosion
is a concern when different types of
metals come into contact as it can degrade
metal interfaces and gasket performance.
*
Exposure to harsh fluids such as jet
and missile fuel, deicing fluid and, in
some cases, the caustic solutions
used to wash down vehicles that
come into contact with nuclear, biological
or chemical (NBC) contaminants,
can degrade EMI materials.
Fortunately, there are materials that
can stand up to these harsh fluids.
For example, fluorosilicone is resilient
amid exposure to jet and missile
fuel and deicing fluid. EPDM performs
reliably even when exposed to
the wash used to remove NBC contaminants.
*
Outgassing is an especially pressing
issue in aerospace applications. When
a material releases a gas or vapor in an
enclosure it can create films and other
coverings over optics, as well as potentially
cause circuit failure.
Adopt a Holistic Approach to
Environmental and Mechanical Testing
The key to testing success is, to the
greatest extent possible, replicating realworld
conditions in a lab environment.
To ensure EMI materials can effectively
operate in rugged environments (and
comply with MIL-STD-802, which governs
environmental performance), engineers
need to complete several qualifying
tests that comprehensively cover
the environmental challenges EMI soluEngineers
can use Highly Accelerated Stress Test chambers to test application performance in high-pressure
and high-temperature environments and perform humidity resistance tests efficiently.
tions may face.
* Standard corrosion testing can be used
for almost all materials and includes
the use of a salt fog chamber, which
creates a warm fog atmosphere of
saline solution where the material is
immersed to assess how it withstands
the environment.
* Fluid exposure testing consists of
soaking materials in fluids and determining
mass or volume swell. The
standard fluid test matrix includes
fuel, hydraulic fluid, lubricating oils,
deicing and antifreeze fluids, and solvents
and cleaners.
* Temperature testing regimens can include
temperature cycling, highly accelerated
stress tests, humidity testing,
and more to verify performance across
a wide range of temperatures.
* To ensure materials (especially metals)
can withstand shock and vibration,
engineers need to perform mechanical
tests. For example, a fatigue analysis
test can determine the lifespan of
metal designs in relation to compressed
heights and stress.
A technician prepares a piece of electronic equipment for environmental testing.
12
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* Accelerated aging models help design
engineers gather accurate data and
better project the lifetime performance
of a wide mix of materials.
Aerospace & Defense Technology, December 2021
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Aerospace & Defense Technology - December 2021

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