TM 1-1500-204-23-11
Figure 4-12. Simultaneous Stitch Process
4-4. LAMINATING RESINS AND STRUCTURAL
not interchangeable unless speciically authorized by
ADHESIVES. The material that binds and supports
engineering.
the ibers in the laminate is called the matrix. We
use the term "laminating resin" to refer to any of the
c. Crosslinking. Once mixed, two part thermoset
two part, thermoset plastic resins that are typically
resin systems like epoxy undergo a chemical reaction
used as matrix materials in composite laminates.
known as "cross-linking". Cross-linking occurs at the
molecular level and binds the molecules of component
a. Laminating Resins. While there are many
A with those of component B forming a solid over a
matrix resin chemistries available (see paragraph 4-5)
period of time. When the cross-linking is complete the
epoxy is by far the most common resin system found
resin is said to be fully "cured". Like most chemical
in Army aviation. Epoxies used as laminating resins
reactions, cross-linking can be accelerated with heat,
tend to be fairly low viscosity (generally less than
thus reducing the cure time. For example, an epoxy
5000 CPS) meaning they re fairly "thin" or "runny".
that normally cures in 5 days at room temperature
This is necessary in order to thoroughly saturate the
(77 F) may be fully cured in only 1 hour at 180 F.
ibers and allow air and other gasses to escape as
the resin cures. This lower viscosity often affects the
d. Fiber-dominated Properties. Fiber-dominated
resin s adhesive characteristics to a small degree, but
properties are those physical properties of the lam-
it s worth the trade off to get a high quality laminate.
inate that are governed by the properties inherent
in the ibers used, i.e. carbon iber, iberglass, or
b. Structural Adhesives. Superior adhesive prop-
Kevlar. Tension and lexural strength are iber-dom-
erties are the primary consideration when making
inated properties.
structural adhesives. Thinner materials generally move
away from the bondline where it is needed. Higher
e. Matrix-dominated Properties. Just as we have
viscosity is almost always a feature of structural adhe-
iber-dominated properties in a laminate, we also
sives when compared to laminating resins. Structural
have matrix-dominated properties. Matrix-dominated
adhesives are often thickened by the addition of
properties are those physical properties of the laminate
either illers or a chemically reactive modiier. These
that are governed by the properties inherent in the
adhesives are used for adhesively bonding structures
matrix used. Compression, shear, and interlaminar
together, bonding in core materials, as well as repair
shear are all matrix-dominated properties as is service
patches. They are also used as a "liquid shim" in a
temperature.
bonded or bolted structure to ill any gaps left during
assembly. Both laminating resins and structural adhe-
f. Service Temperature. Whether used in man-
sives are two component systems that require careful
ufacturing or repair, one of the most important
weighing and thorough mixing to ensure strength is
matrix-dominated properties for selecting an epoxy
not compromised. Because of their different viscosi-
is the anticipated service temperature of the part.
ties, laminating resins and structural adhesives are
