Toughened carbon fiber epoxy
Efforts to develop an improved
carbon fiber epoxy resin system date
back to the early- to mid-1980s. These
efforts also originated with Boeing’s
in-service fleet experience. Since the
production of the 757 and 767, airline
customers have had to contend with
thin-gage composite structures in a
wide number of applications. Complaints
about this material’s sensitivity
to impact damage and the difficulty
of repair were many.
In response to these complaints,
Boeing initiated and led a significant
effort to develop a toughened epoxy
matrix that would be more resistant
to damage. Supplier efforts were repeatedly
thwarted by the negative impact
of toughening agents on hot/wet
compression strength.
Fortunately for Boeing, Toray had
been working diligently on a resin
system that involved a toughening interlayer.
The resulting system set a
new standard for toughness and
strength in composite material technology.
Impact test results demonstrated
to the airlines that this new
system also suffered significantly less
damage, and that such damage could
be repaired in a manner similar to repair
of existing aluminum structures.
This breakthrough in CFRP toughness
was optimized to enable Continuous
Tape Laying Machines (CTLM)
to fabricate structures, resulting in reduced
manufacturing costs. The new
toughened matrix CFRP is used for
the main box cover panels and the
main box spars. The main torque box
cover panel consists of an integrally