01 March 2005
NAVAIR 01-1A-509-1
TM 1-1500-344-23-1
TO 1-1-689-1
Table 3-2. Effects of Deterioration on Nonmetals
TYPE OF ATTACK TO WHICH
APPEARANCE OF
MATERIAL
MATERIAL IS SUSCEPTIBLE
DETERIORATION
Acrylic
UV light, moisture, solvents
Discoloration, cracking
Adhesive
Dirt, UV light, solvent, moisture
Cracking, peeling
Ceramic
Extreme heat
Discoloration, cracking
Cloth
Dry rot, mildew
Discoloration, tears, dust
Moisture, scratchess
Peeling, flaking, bubbling
Cork
Moisture, mildew, dry rot
Discoloration, dust, peeling
Elastomer
Heat, UV light, excessive cycling
Cracks, crazing, discoloration
Encapsulation
UV light, moisture
Cracking, peeling, disbonding
Felt
Moisture, mildew
Discoloration, looseness
Glass
Heat, mechanical damage (broken)
Cracked, discolored
Laminates
UV light, moisture, solvents
Discolored, disbond, delamination
Paint
Moisture, heat, humidity
Bubbles, peeling, cracking
Plastic
UV light, heat, abrasion
Discoloration, cracks, deformation
Polymers
Extreme heat, solvents
Discoloration, deformation
Potting Compounds
UV light, moisture, heat
Discoloration, cracks, deformation
RTV (noncorrosive)
Moisture, UV light, heat
Peeling, debonding, discoloration
Sealants
Moisture, UV light, heat
Peeling, debonding, discoloration
mechanical failure through cracking, and altering of
assembly. These materials are considered nearly as
electrical characteristics. The most common nonmetals
effective as hermetic sealing. Typical materials used for
used in aircraft systems and their modes of deterioration
this purpose are epoxy, polyurethane, silicone rubber,
are listed in Table 3-2. Examples of nonmetallic
acrylic, and varnish. Because these materials are
deterioration are discussed in the following paragraphs.
organic, they are susceptible to moisture, varying
temperature, and fungus. Moisture accumulates when
3-11.1. GRAPHITE/CARBON FIBER COMPOSITES.
incorrect repair procedures cause imperfections and
Graphite or carbon fiber composites are materials which
bubbles, or when the coating is applied too thick. High
consist of reinforcing fibers in a matrix made of organic
temperatures may cause corrosive vapor to outgas
resin, usually epoxy. They are an important class of
from encapsulants and conformal coatings. This
aviation materials because of their high strength-to-
problem is of special concern if a circuit component
weight ratios and high stiffness. Composite materials
burns on a conformal coated circuit board. These
are found in aircraft structure, connectors, enclosures,
gaseous vapors can penetrate under circuit board
EMI seals and gaskets. Since carbon is the least active
coatings and cause major corrosion damage.
metal in the galvanic series, it will accelerate the
corrosion of any aircraft metal to which it is coupled.
3-11.3. POTTING COMPOUNDS. Potting compounds
Insulation between graphite or carbon epoxy
are used to encase a part or component, such as in an
composites and other metals is necessary to prevent
electrical connector. Generally, potting compounds
dissimilar metal attack on the attached part.
are considered to be a good seal against moisture
when correctly applied. Problems occur when potting
3-11.2. E N C A P S U L A N T S A N D C O N F O R M A L
compounds are cured too quickly, not mixed properly,
COATINGS. Encapsulants and conformal coatings are
or the surface is not cleaned completely. Aging of
used to envelop an avionic component, module or
certain potting compounds can cause the potting
compound to harden and become brittle, or soften and
