19-12-2012, 06:07 PM
ELECTRON BEAM PROCESSING FOR AIRCRAFT STRUCTURES
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Abstract
A low cost electron beam curable epoxy resin
system was developed. The strength of QC130-34-
154A using this resin system with toughening agent
was almost same as QC130-31-154A developed in
FY2004 and the cost reduction was 60%. QC130-
34-154A was fully cured by irradiating 30 kGy. A
trial fabrication of the “H” cross-sectional beam
was carried out with the continuous pre-forming
device. Electron beam of 30 kGy per each pass and
the total dose of 120 kGy were irradiated to the preform.
The quasi-isotropic SBS strength was 43MPa
which was equal to the thermally cured. The
electron beam dose distribution of the floor beam
was measured and uniform distribution was
confirmed with a scattering plate.
Introduction
Autoclave process, which requires high energy
consumption, is usually used for CFRP fabrication
of aircraft structures. Advanced Pultrusion (ADP) is
an automated continuous fabrication system using an
oven to fabricate stringers and floor beams. It
reduces fabrication cost but requires long time to
cure thermosetting material.
Material Development
Materials
QC130-34-154A prepreg was developed to
reduce cost as same as the conventional prepreg, and
almost 60% reduction compared to QC130-31-154A
prepreg developed in FY2004. And also the
toughness improvement was designed by adding
toughening agent. Carbon fiber BESFIGHT IM600-
24K (Toho Tenax Co., Ltd) was used and the resin
system consists of bisphenol-A epoxy, flow control
agent, toughening agent, and cationic photo initiator.
Fiber areal weight was 150 g/m2 and resin content
was 35 wt%. A resin system for the bending test of
the resin plate was the same composition as QC130-
34-154A except flow control agent.
Procedures
The bending test of the resin plate was
conducted by JIS K 7171, and the specimens were
thermally cured by 180 deg C, 2-hour.
For the degree of cure measurement, prepregs
were hand lay-upped to 40-ply (approx. 6 mm
thickness) using vacuum bag and cured by 10-150
kGy electron beam of 10 MeV irradiation device at
Nuclear Fuel Industries, LTD. Differential scanning
calorimetry (DSC) test was conducted by JIS K
7122; 10 deg C /min heat up rate, 50 ml/min flow
rate nitrogen atmosphere.
FRP mechanical tests were performed on
electron beam cured laminates using QC130-34-
154A prepreg. Prepregs were hand lay-upped and
heat debulked in an autoclave using vacuum bag; 0.5
MPa pressure, 90 deg C temperature hold for 10
minutes, and cured by 120 kGy electron beam. Fiber
volume contents (Vf) of the cured specimens were
approximately 55%. Testing condition was room
temperature and specimens were prepared by dry
condition. Tensile, compression, in-plane shear,
open-hole compression (OHC) and short beam shear
(SBS) test were conducted by ASTM-3039,
SACMA SRM 1M, ASTM-3518, ASTM-6484 and
ASTM-2344. Test data was normalized to 60% Vf
except SBS test.
Continuous Fabrication
The “H” cross-sectional beam was fabricated
with a continuous pre-forming device using QC130-
34-154A prepreg. The ply orientation of the H beam
was quasi-isotropic [45/90/-45/0]2S. The prepreg was
cut into each oriented fiber direction tapes, laid up to
4 rolls and set up to the pre-forming stand. The
prepreg rolls were intermittently pulled and
gradually pre-formed into the “H” shape. In the
molds, the pre-form was pressed for a specified time,
released from the molds and pulled to a specified
feed pitch. One cycle of pre-forming consists of
pressing period and moving period as illustrated in
Fig. 3. The pre-form was carried to the 10 MeV
irradiation device at Nuclear Fuel Industries, LTD
and electron beam of 30 kGy per each pass and the
total dose of 120 kGy were irradiated to the pre-form
on the 45 degree sloped table. The pre-forming
condition, thickness and SBS strength of the cured
pre-form are shown in Table 3. SBS strength of
43MPa which is equal to the hand lay-upped and
thermally cured was obtained.
Conclusions
A low cost electron beam curable epoxy resin
system was developed. The strength of QC130-34-
154A was almost same as QC130-31-154A and high
degree of cure was attained by 30 kGy for QC130-
34-154A.
A trial fabrication of the “H” cross-sectional
beam was carried out with the continuous preforming
device. Electron beam of 120 kGy were
irradiated to the pre-form and the quasi-isotropic
SBS strength was 43MPa which was equal to the
thermally cured.
The electron beam dose distribution of the
floor beam was measured and uniform distribution
was confirmed with the use of a scattering plate.