SAMPE Journal - July/August 2016 - 33

Feature Article
Primary Factors:
a) Tack levels
b) Heat settings
c) Compaction forces
d) Machine course widths
e) Tow path tension
f) Core spacing
g) Ramp angles
h) Conical vs. square corners
Figure 4. Developing AFP process parameters at core ramps requires attention to several factors.

the evacuation of air and volatiles in the baseline
hand lay-up material form are assessed for their
impact on panel void content. For this effort panels
are fabricated using the placement parameters
from the established process envelope for heat and
compaction.
Cure Methodology Optimization. Once the optimized
bagging scheme has been determined, the next set
of panel trials serve as a platform to explore varied
cure cycles. These trials focus on altering the cure
cycle (verified with the material supplier) to increase
volatile extraction. Panels are fabricated using the
selected parameters from the established heat and
compaction process envelope and are identical to
the parameters selected for the bagging trials.
Mechanical Characterization. Once an optimized
bag and cure methodology are selected, the
processing envelope is validated by mechanical
testing. Typically, this mechanical testing includes
unnotched compression, open-hole tension and
compression, and bearing. Multiple parameters
selected from the heat and compaction optimization
should be evaluated.
Geometric Features on Flat Surfaces
Continuing with the building block approach,
Lockheed
Martin
explores
manufacturing
challenges associated with placement of typical
skin features. All features are initially investigated
on flat surfaces in order to isolate and focus on
the types of impacts the design features have on
manufacturing producibility.
Door and Skin Joggles
Aircraft surfaces usually contain offsets, referred
to as joggles, to allow for an outside flush fit of
components such as access doors. The most
common defect associated with this feature
is bridging. Bridging is a condition where the
material covers a feature without full contact with
SAMPE Journal, Volume 52, No. 4, July/August 2016

the surface. While bridging can occur during fiber
placement in any area with a dramatic change in
contour, it is common over joggles with typical
ramp angles of 20° to 45° as shown in Figure 3.
Bridged tows yield highly localized voids and
surface dryness. The optimized AFP, bagging and
cure conditions established during the process
envelope development are used as the starting
point for developing optimal process parameters
for the joggles. The parameters to be re-evaluated
include roller length, roller durometer, compaction
force, machine heat settings and speed.
Core Ramps
Encapsulated sandwich structure (shown in
Figure 4) occurs when core pieces are inserted
into a lay-up and the core edges are closed off by
the laminate via a core ramp. This configuration
contains transition from solid laminate to sandwich
structure within the same part. Lockheed Martin
has focused most of our development efforts on 20°
ramp angles. Since bridging is one of the primary
defects associated with core ramps, tack levels of
the material, compaction forces, and tow tension
are important elements to consider.

Figure 5. Steering trials conducted on concave tooling.
33



Table of Contents for the Digital Edition of SAMPE Journal - July/August 2016

Contents
SAMPE Journal - July/August 2016 - Cover1
SAMPE Journal - July/August 2016 - Cover2
SAMPE Journal - July/August 2016 - Contents
SAMPE Journal - July/August 2016 - 2
SAMPE Journal - July/August 2016 - 3
SAMPE Journal - July/August 2016 - 4
SAMPE Journal - July/August 2016 - 5
SAMPE Journal - July/August 2016 - 6
SAMPE Journal - July/August 2016 - 7
SAMPE Journal - July/August 2016 - 8
SAMPE Journal - July/August 2016 - 9
SAMPE Journal - July/August 2016 - 10
SAMPE Journal - July/August 2016 - 11
SAMPE Journal - July/August 2016 - 12
SAMPE Journal - July/August 2016 - 13
SAMPE Journal - July/August 2016 - 14
SAMPE Journal - July/August 2016 - 15
SAMPE Journal - July/August 2016 - 16
SAMPE Journal - July/August 2016 - 17
SAMPE Journal - July/August 2016 - 18
SAMPE Journal - July/August 2016 - 19
SAMPE Journal - July/August 2016 - 20
SAMPE Journal - July/August 2016 - 21
SAMPE Journal - July/August 2016 - 22
SAMPE Journal - July/August 2016 - 23
SAMPE Journal - July/August 2016 - 24
SAMPE Journal - July/August 2016 - 25
SAMPE Journal - July/August 2016 - 26
SAMPE Journal - July/August 2016 - 27
SAMPE Journal - July/August 2016 - 28
SAMPE Journal - July/August 2016 - 29
SAMPE Journal - July/August 2016 - 30
SAMPE Journal - July/August 2016 - 31
SAMPE Journal - July/August 2016 - 32
SAMPE Journal - July/August 2016 - 33
SAMPE Journal - July/August 2016 - 34
SAMPE Journal - July/August 2016 - 35
SAMPE Journal - July/August 2016 - 36
SAMPE Journal - July/August 2016 - 37
SAMPE Journal - July/August 2016 - 38
SAMPE Journal - July/August 2016 - 39
SAMPE Journal - July/August 2016 - 40
SAMPE Journal - July/August 2016 - 41
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SAMPE Journal - July/August 2016 - 72
SAMPE Journal - July/August 2016 - Cover3
SAMPE Journal - July/August 2016 - Cover4
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